Soil Improvement State-of-the-Art Report

Transcription

1 Session 12 Soil Improvement State-of-the-Art Report Amélioration des Sols J.K. MITCHELL Professor and Chairman of Civil Engineering, University of California, Berkeley, CA, USA SYNOPSIS Because of the increasing need to utilize marginal sites and because many soils can be made into useful construction materials if properly treated, soil improvement has become a part of many present day civil engineering projects. In this state-of-the-art report the principles, applications, and design procedures for soil improvement using different methods are presented. Soil improvement methods reviewed include in-situ deep compaction of cohesionless soils, precompression with and without vertical drains, injection and grouting, admixture stabilization, thermal methods, and soil reinforcement. Comprehensive recent references on each topic are listed. INTRODUCTION Most of man's construction is done on, in, or with soil. As the availability of suitable construction sites decreases, the need to utilize poor soils for foundation support and earthwork construction increases. In addition, it is becoming increasingly necessary to strengthen the ground under existing structures to insure stability against adjacent excavation or tunneling, or to improve resistance to seismic or other special loadings. Furthermore, many hundreds of recent successful projects have shown that through the use of suitable reinforcement materials and systems, the uses of nature's most abundant construction material soil--can be greatly extended. It is not surprising, therefore, that the general area of soil improvement and reinforcement has been of great interest and rapid development in the past several years. The inclusion of this topic for the first time as a main session in an International Conference of our Society is clear recognition of this fact. The basic concepts of soil improvement; namely, drainage, densification, cementation, reinforcement, drying, and heating, were developed hundreds or thousands of years ago and remain valid today. The coming of machines in the 19th century resulted in vast increases in both the quantity and quality of work that could be done. Among the most significant developments of the past 50 years are the introduction of vibratory methods for densification of cohesionless soils, new injection and grouting materials and procedures, and new concepts of soil reinforcement. The purpose of the present report is to synthesize the present state-of-the-art of soil improvement into a form suitable for direct application by practicing engineers. At the same time the author has attempted to identify sufficient references that interested readers will be able to locate more detailed information, case histories, etc. Emphasis in this report is on practical aspects of soil improvement, to include such considerations as soil types best suited for treatment, effective treatment depths, properties of treated soils, major applications, and relative costs. Because of the extensive scope of the subject the inclusion of detailed case histories is not possible. METHODS AND SCOPE The Conference Organizing Committee has identified the following topics for discussion in Session 12, so they have been chosen for coverage in this state-of-the-art report. 1. Compaction, especially heavy tamping and blasting. Emphasis is on in-situ deep densification of cohesionless soils, and compaction in thin layers is excluded. 2. Consolidation by preloading and/or vertical drains, electro-osmosis. 3. Grouting, excluding control of groundwater flow and seepage. 4. Soil stabilization using admixtures and by ion exchange (chemical stabilization). Emphasis is on new developments and applications other than subgrades and base courses for roads and airfields. 5. Thermal stabilization. 6. Reinforcement of soil. Emphasis is on the inclusion during construction or installation in-situ of both tensile and compression reinforcement elements. Geotextiles used as reinforcement are included. The report concludes with a tabular summary of the methods discussed and consideration of factors governing the choice of a method for any given case. 509

2 DEEP COMPACTION OF COHESIONLESS SOILS Introduction Thick deposits of loose cohesionless soils may require improvements in order to eliminate the subsequent development of excessive total and differential settlements and to minimize the possibility for liquefaction under dynamic loading. Suitable improvement can be achieved in many cases by densification; however, the needed densification cannot ordinarily be achieved using preload surcharge fills or compaction at the surface. In-situ densification of loose, cohesionless soil layers is usually done by dynamic methods. In many methods dynamic loading is accompanied by displacement in the form of the insertion of a probe and/or construction of a sand or gravel column in-situ. Methods that are used for the in-situ deep densification of cohesionless soils include blasting, vibrocompaction, and heavy tamping. Vibrocompaction is used herein to refer collectively to all those methods involving the insertion of vibrating probes into the ground with or without the addition of a backfill material. Compaction piles are also considered in this category. The ability of any of these methods to accomplish the needed improvement in properties depends on several factors, including: 1. Soil type, especially its gradation and fines content 2. Degree of saturation and water table location 3. Initial relative density 4. Initial in-situ stresses 5. Initial soil structure, including the effects of age, cementation, etc. 6. Special characteristics of the method used. Mechanism of Densification Densification of cohesionless soil layers with accompanying improvement in mechanical properties requires first that the initial soil structure be broken down so that particles can be moved to new packing arrangements. In saturated cohesionless materials this is most readily accomplished by inducing liquefaction by means of dynamic and cyclic loadings. In the case of methods such as blasting and heavy tamping the compression wave generated by the sudden large energy release can give an immediate build-up in pore water pressure which greatly reduces the shear strength. This wave is followed by a shear wave which is responsible for failure of the mass. After passage of these waves the soil particles settle into new and, ultimately, more stable positions. Vibrocompaction methods are effective in much the same way, except that the energy per event is many times smaller, the vibrations continue over a much longer period, and the effects are felt to distances from the energy source of one to two meters instead of up to 10 m or more as is the case with blasting and heavy tamping. For partly saturated soils, including some containing fines and many waste fills, densification is mainly by collapse of the soil structure and escape of gas from the voids. The process is much the same as densification by impact compaction as commonly done in the laboratory. Densification accompanying ground treatment by these methods occurs rapidly. Settlement of the ground surface is essentially complete by the end of treatment. Improvement in properties, as measured, for example, by penetration tests or pressuremeter tests, may continue over extended time periods. This latter point may be of considerable practical importance in the evaluation of ground treatment. Experience has indicated that it is often easier to densify to a specified high relative density from a loose initial condition than from an intermediate relative density. This is because the initial structure of the loose material is easier to break down. Soil Type Considerations Vibrocompaction methods are best suited for densification of clean, cohesionless soils. Experience has shown that they are generally ineffective when the percentage by weight of fines (particles finer than 200 mesh sieve or mm diameter) exceeds 20 to 25. This is because the permeability of materials containing greater percentages of fines is too low to allow the rapid drainage of pore water that is required for densification following liquefaction under the action of the vibratory forces, and because the structure may be more difficult to disrupt owing to cohesion contributed by the fines. Some soils containing greater amounts of fines; e.g., some silty sands and loess, can be densified by blasting and/or heavy tamping, both of which impart large amounts of energy all at once and cause large ground displacements. More specific considerations concerning the influences of soil type are presented in the discussion of particular methods. For preliminary planning, however, it may be considered that the range of particle size distributions shown by Fig. 1 will be best suited for densification by deep in-situ methods. Evaluation of Treated Ground Measurement of the effectiveness of deep compaction can be made using one or more of several methods. Techniques that have been used include: 1. Surface settlement markers 2. Volume of soil added to fill craters, to form compaction piles, or to carry out a vibrocompaction process 3. Standard Penetration Tests (SPT) 4. Cone Penetration Tests (CPT) 5. Pressuremeter Tests (PMT) 6. Seismic shear wave velocity determinations 7. Pile driving resistances 8. Plate load tests 5 1 0

3 Sand U. 40 i Most Desirable Size Range (Vibroflotation) Thorburn (1975) Particle Size - mm Fig. 1 Range of Particle Size Distributions Suitable for Densification by Vibrocompaction 9. Down-hole density meters. Settlement measurements and SPT, CPT, or PMT are the most commonly used methods. The CPT is particularly useful because it provides a continuous record of penetration resistance with depth, it is fast, and it is well-suited for use in sands. Penetration tests for evaluation of improved ground are usually done at locations intermediate between probe points in order to provide the most conservative estimate of improvement. Penetration resistance values, both before and after ground improvement, are often converted to relative densities using one or more of several correlations that have been developed for particular conditions. Design criteria and specifications are many times developed in terms of relative density. A direct conversion of a penetration resistance to relative density is uncertain, however, because penetration resistance depends on factors other than density. The correlations are not independent of soil type. Increased lateral pressure, increased time under pressure, increased stability of structure, and prior seismic strains lead to increased penetration resistance (Seed, 1979). Fortunately, these latter factors also lead to corresponding increases in resistance to settlement and liquefaction, and it is the penetration resistance values themselves that are important, not the actual relative density. It has been found convenient for some applications, however, to work with an "equivalent relative density" which is the true relative density a sand deposit would have to possess to exhibit the measured penetration resistance if it were freshly deposited and normally consolidated. Approximate correlations between equivalent penetration resistance, sand density and properties pertinent to the assessment of foundation stability are given in Table I. In a few cases instrumentation has been used to monitor conditions during densification. Total pressure cells and piezometers have provided data useful for developing improved understanding of the densification and property improvement process. Blasting Deep compaction by detonation of buried explosives can provide a rapid, low cost means for soil improvement in some cases. The general procedure consists of: 1. Installation of pipe by jetting, vibration, or other means to desired depth of charge placement 2. Placement of charge in pipe 3. Backfilling the hole 4. Detonation of charges according to a preestablished pattern. In some cases the pipe is withdrawn prior to detonation of the charges. In others it is reclaimed after the blast, a new section is welded to the bottom, and it can be used again. The explosives used include dynamite, TNT, and ammonite. Detailed descriptions of blasting are given by Prugh (1963), Ivanov (1967), Mitchell (1970), Litvinov (1973, 1976), Damitio ( ), Donchev (1980), and others

4 TABLE I Penetration Resistance and Sand Properties Very Loose Loose Medium Dense Dense Very Dense SPT N-value (blows/0.3m)* CPT cone resistance (kg/cm2)* Equivalent Relative Density (%)** Dry Unit Weight (kn/m3) < > 50 < >200 < < > 20 Friction Angle ( ) < > 38 Cyclic Stress Ratio Causing Liquefaction (T/ao ')*** < >0. 35 *At an effective vertical overburden pressure of 100 kpa. **Freshly deposited, normally consolidated sand. ***From Seed (1979), Fig. 6(a). Saturated, clean sands are well-suited for densification by blasting. Success in any case depends on the ability of the shock wave generated by the blast to break down the initial structure, and create a liquefaction condition for a sufficient period to enable particles to rearrange themselves in a denser packing. It follows, therefore, that the stronger the sand initially, the larger the charges that will be required for effective densification. Thus, the greater the depth to which densification is needed and the higher the initial equivalent relative density, the greater the explosive energy required. There appear to be no generally accepted theoretical design procedures for densification by blasting, and field trials are usually used prior to production blasting. A number of field cases have been summarized by Ivanov (1967) involving treatment depths up to 20 m. From these experiences the following general guidelines emerge : 1. Charge size: <1 to 12 kg 2. Depth of burial: >1/4 depth to bottom of layer to be treated; 1/2 to 3/4 of depth common 3. Charge spacing in plan: 5-15 m 4. Number of coverages: 1-5 with 2-3 usual. Each coverage consists of a number of individual charges. Successive coverages are usually separated by hours or days. 5. Total explosive use: gm/m3, gm/m3 typical 6. Surface settlement: 2 to 10% of layer thickness. The maximum depth to which blasting can be used successfully for soil compaction is not known. The author is currently associated with a project in which charges of up to 30 kg have been detonated at depths more than 40 m below ground surface. Significant surface settlements and improvement in the equivalent relative density of loose zones at depths greater than 30 m have been achieved. An interesting feature of this work is the observation that although surface settlement is immediate, which means that densification is also essentially immediate, results of cone penetration tests do not indicate an increase in equivalent relative density to the required value for several weeks, reflecting an aging or healing effect following disruption of the initial structure and formation of a new one. It would be expected that the maximum depth for effective treatment will be limited by the practical difficulty of placing concentrated charges of sufficient magnitude to create a shock wave great enough to liquefy the initial soil structure. As the depth increases, so do the effective stresses and strength. Accordingly, the required disruptive stress will increase, and the effective radius of influence will decrease. The magnitudes of the shock wave pressure, Pmax in kg/cm2, and the impulse per unit area, I, in kg-sec/cm2,are given by Ivanov (1967) as follows hc/171 - k-i JS I

5 in which C R 1 =k2(if)(3lif)u2 (2> y,u = size of charge (kg of TNT) = distance from center of charge (m) = empirical coefficients from Table II. These relationships can be used for comparative studies of the probable influences of charge size, charge spacing, and sand saturation. It may be seen that the presence of even small amounts of gas leads to significant damping of the P-wave pressure. It has been possible by blasting to densify sands to equivalent relative densities of 75 to 80 percent. In some cases, however, the results may be erratic, initially dense zones may be loosened, and the method is not likely to be effective in the upper one or two meters below the ground surface. Typical behavior may be summarized as follows. 1. Almost immediate settlement of the ground surface, with little further settlement with time. 2. Initially loose zones show little immediate change in penetration resistance. Penetration resistance increases slowly with time until after several weeks the material indicates a marked improvement in properties compared to its initial condition. 3. Zones which are initially very dense may be permanently loosened or weakened by the blast; however, the resultant condition is still likely to be satisfactory. 4. Ultimately, an effective blasting program results in a deposit in which all the initially loose zones have been suitably improved. When a series of coverages is used, the surface settlement accompanying each coverage is usually less than the one preceding. Attempts have been made to compact using surface explosions, because of simplicity, low cost, and speed. Because of energy loss above ground, lack of confinement, and the formation of surface depressions, however, this method has been of limited effectiveness. A hydro-blasting technique has been used very successfully and economically for compaction of collapsible loess deposits (Litvinov, 1973, 1976; Donchev, 1980). Although collapse of the loess can often be accomplished by flooding alone, it has been found that more uniform results can be achieved more quickly and economically by this method. The procedure, which is illustrated in Fig. 2, consists of first cutting a contour trench 0.2 m to 0.4 m wide and several meters deep around the perimeter of the area to be densified. Boreholes spaced a few meters apart in a grid pattern are then used to pump water into the loess, over a period of several days, ideally until the water content is increased to above the liquid limit. Slurry walls or plastic membranes can be installed to prevent lateral migration of the water and softening of adjacent ground. Explosive charges of about 5 kg each are then inserted down tubes installed at spacings of three to six meters in grid patterns and detonated. Surface settlements of up to 10 percent of the layer thickness and reduction in porosity of several percentage points are not uncommon. Areas of 1000 m 2 to 10,000 m 2 involving 10, ,000 m 3 of loess can be treated at one time. Successful compaction of saturated sand and collapsible loess has been accomplished in the USSR using high energy, high voltage electrical discharges from probes inserted in the ground (Lomize et al., 1963, 1973). Each discharge, which may release 50 to 100 kj of energy, has an effect similar to that of an explosion of comparable magnitude. A number of discharges are released spaced at intervals of several seconds at each level as the probe is moved upwards from the bottom. It appears that use of this method has not yet been widely adopted. TABLE II Parameters for Estimating Blast Pressures and Impulse Values (from Ivanov, 1967) Gas Content (%) kl yl k2 y2 Sand below water table Moist sand (8-10% water) (2-4% water) V olym e

6 15 Hz and a vertical amplitude of mm. About 15 probes per hour can be done at spacings of 1 to 3 m. It is of marginal effectiveness in the upper 3 to 4 m of the zone to be densified. Vibro-rods developed by Saito (1977), Fig. 3, are also driven using a vibratory pile driving hammer. Several cycles of insertion and withdrawal are used in the densification process. I Uncompacted Uncompacted Soils Compacted Area Soils Section A -A Fig. 2 Loess Compaction by Hydro-Blasting Vibrocompaction and Compaction Piles These methods for deep compaction of cohesionless soils are characterized by the insertion of a cylindrical or torpedo-shaped probe into the ground followed by compaction by vibration during withdrawal. In a number of the methods a granular backfill is added so that a compacted sand or gravel column is left behind within a volume of sand compacted by vibration. Sinking of the probe to the desired treatment depth is usually accomplished using vibratory methods, often supplemented by water jets at the tip. Injection of air at the same time has been found to facilitate penetration to large depths. Upward directed water jets along the sides has also been found helpful in some cases. Soil gradations suitable for densification by vibrocompaction are indicated in Fig. 1. Compaction piles of sand and gravel formed by these methods are also used in soft cohesive soils, in which case they function as compression and shear reinforcement, as discussed in a later section of this report. Ground treatment depths of 20 m can be achieved routinely by these methods. Depths in excess of 30 m can be attained in some cases. A brief description of some of the more extensively used vibro-compaction methods is given below. 1. Vibrating Probes The Terraprobe method, developed in the U.S.A. (Anderson, 1974), uses a Foster Vibrodriver pile hammer on top of a 0.76 m dia. open tubular probe (pipe pile) that is 3 to 5 m longer than the desired penetration depth. The unit operates at a frequency of (a) Double Tube Rod (b) Rod With Projectives Fig. 3 Vibro-Rods Used for Sand Densification 2. Vibroflotation (from Saito, 1977) This method was developed in Germany almost 50 years ago, and its development has continued there and in the U.S.A. where it was introduced in the 1940's. The equipment consists of three main parts: the Vibrator, extension tubes, and a supporting crane. A schematic diagram of the equipment and process is given in Fig. 4. The vibrator is a hollow steel tube containing an eccentric weight mounted on a vertical axis in the 5 1 4

7 Motor V ib ra to r E X TEN SIO t T U B E S SuPPir OP B GRANULAR L SO IL M A T E R IA. Casing pipe W A T E R SUPPLY W A T E R SU PP LY c o m p a c t e d. 4 ZONE Z^W/T" C O H E S IO N L E S S S O IL lower part so as to give a horizontal vibration. Vibrator diameters are in the range of 350 to 450 mm and the length is about 5 m including a special flexible coupling. One vibrator weighs about 20 kn. Units developing centrifugal forces up to 160 kn and variable vibration amplitudes of up to 25 mm are available. Most usual operating frequencies are 30 Hz and 50 Hz. The extension tubes have a slightly smaller diameter than the vibrator and a length dependent on the depth of penetration required. Vibroflot sinking rates of 1 to 2 m/min and withdrawal/compaction rates of about 0.3 m/min are typical. Water pressures of up to 0.8 MPa and flow rates up to 3,000 1/min may be used to facilitate penetration. Sand backfill is consumed at a rate of up to 1.5 m 3/m during the compaction process. The zone of improved soil extends from 1.5 m to 4 m from the vibrator, depending upon soil type and vibroflot power. Additional details are presented by Baumann and Bauer (1974), Bell (1975), and Brown (1977), among others. 3. Vibro-Compozer Method This sand compaction pile method was developed by Murayama in Japan in 1958 (Murayama, 1958). The apparatus and procedure used in the compozer system are shown schematically in Fig. 5. A casing pipe is driven to the desired depth by a vibrator at the top. A sand charge is then introduced into the pipe, the pipe is withdrawn part way while compressed air is blown down inside the casing to hold the sand in place. The pipe is vibrated down to compact the sand pile and enlarge its diameter. The process is repeated until the pipe reaches the ground surface. The resulting pile is usually 600 to 800 mm in diameter. The actual diameter can be estimated from the sand volume discharged into the ground. 4. Soil Vibratory Stabilizing Method This method, termed both the SVS method and the Toyomenka method, combines both the Fig. 5 Construction of Compaction Piles by the Compozer System vertical vibration of a vibratory driving hammer and the horizontal vibration of a Vilot depth compactor. The Vilot is a special probe of about the same size as vibroflot units. Sand backfill is used, but water is not used in either the sinking or compaction process. The gradation of both the in-situ soil and the backfill, which may or may not be the same material, influence the level of improvement that may be obtained. Coarse sands give greater densification than fine sands, evidently because the coarser material is better able to transmit vibrations. Brown (1977) has defined a suitability number for vibroflotation backfills that is given by Suitability Number 1.7 (D 2 0 ' <Dio)2 in which D^g, D20» and are the 50, 20, and 10 percent size grain diameters in mm. Corresponding suitability numbers and backfill ratings are 0-10 Excellent Good Fair Poor > 50 Unsuitable The lower the suitability number the faster the vibroflot can be withdrawn while still achieving acceptable compaction. The influence of fines on the level of improvement that can be obtained by vibrocompaction is shown clearly by the data in Fig. 6 (Saito, 1977). The data provide excellent support for the rule of thumb that vibrocompaction is ineffective in soils containing more than 20 percent fines. Bhandari (1977) describes a case in which compaction piles led to soil densification only in zones where the fines content was less than 20 percent. (3) 5 1 5

8 4 0 S = it (1 + e ) o 1/2 (5) <D A3 > in 4 c3 O o \ / \ * y *. *. \ > <? -t V * 3 arovement f o r p i l e s in a t r i a n g u l a r p a t t e r n, Fig. 7(b), i n w h i c h d is t h e s a n d p i l e d i a m e t e r (up to 800 mm). A n i n f l u e n c e c u r v e m e t h o d t h a t c a n be u s e d to e s t i m a t e v i b r o f l o t a t i o n p r o b e s p a c i n g s t o g i v e a s p e c i f i e d m i n i m u m r e l a t i v e d e n s i t y is g i v e n by B r o w n (19 77). B r o w n ' s c u r v e s a r e b a s e d o n the p r o c e d u r e d e v e l o p e d b y D ' A p p o l o n i a (1953) ft T " * - Before irr provement Finer fraction : < 74/* 30 % Fig. 7 (b ) T ria n g u la r P a tte rn U s u a l V i b r o c o m p a c t i o n a n d C o m p a c t i o n P i l e P a t t e r n s Fig. 6 E f f e c t o f F i n e s C o n t e n t o n I n c r e a s e in P e n e t r a t i o n R e s i s t a n c e b y V i b r o c o m p a c t i o n ( from S aito, 1977) E m p i r i c a l d e s i g n c u r v e s f o r v i b r o c o m p a c t i o n h a v e b e e n d e v e l o p e d b y T h o r b u r n (1975). Fig. 8 is a r e l a t i o n s h i p b e t w e e n t h e r e l a t i v e d e n s i t y of a In s o m e i n s t a n c e s p e n e t r a t i o n r e s i s t a n c e s a r e so h i g h f o l l o w i n g d e n s i f i c a t i o n b y v i b r o c o m p a c t i o n t h a t r e l a t i v e d e n s i t i e s g r e a t e r t h a n 100 p e r c e n t a r e i n d i c a t e d a c c o r d i n g to c o n v e n t i o n a l c o r r e l a t i o n s. I n r e a l i t y, h o w e v e r, t h i s r e s u l t is in m o s t i n s t a n c e s c a u s e d b y t h e i n c r e a s e d l a t e r a l p r e s s u r e i n d u c e d b y t h e v i b r a t i o n p r o c e s s. I n - s i t u l a t e r a l p r e s s u r e m e a s u r e m e n t s r e p o r t e d b y S a i t o (1977) y i e l d e d v a l u e s of K q as h i g h as 6 in s o m e z o n e s a f t e r d e n s i f i c a t i o n. V i b r o c o m p a c t i o n o f l a r g e a r e a s is d o n e in a g r i d p a t t e r n, e i t h e r t r i a n g u l a r or r e c t a n g u l a r, w i t h p r o b e s p a c i n g s u s u a l l y in t h e r a n g e o f 1.5 m to 3 m o n c e n t e r s. T h e a c t u a l s p a c i n g s d e p e n d o n t h e s o i l a n d b a c k f i l l types, p r o b e t y p e a n d e n e r g y, a n d l e v e l of i m p r o v e m e n t r e q u i r e d. A l t h o u g h f i e l d t e s t s a r e u s u a l l y d o n e t o f i n a li z e d e s i g n s, t h e r e a r e s o m e g u i d e l i n e s t h a t c a n b e u s e f u l i n p r e l i m i n a r y s t u d i e s. If it is d e s i r e d to i n c r e a s e t h e a v e r a g e d e n s i t y o f l o o s e s a n d f r o m an i n i t i a l v o i d r a t i o e 0 to a v o i d r a t i o e, a n d if it is a s s u m e d t h a t i n s t a l l a t i o n o f a s a n d p i l e c a u s e s c o m p a c t i o n o n l y in a l a t e r a l d i r e c t i o n, the p i l e s p a c i n g s m a y be d e t e r m i n e d u s i n g 1/2 (4) Spocings of Centers of V ib ra tion-m f o r s a n d p i l e s in a s q u a r e p a t t e r n. Fig. 7(a), a n d Fig. 8 R e l a t i v e D e n s i t y o f C l e a n S a n d at P o i n t s M i d w a y B e t w e e n C e n t e r s o f V i b r a t i o n as a F u n c t i o n o f P r o b e S p a c i n g ( T h o r b u r n, 1975) 516

9 c l e a n s a n d a t p o i n t s m i d w a y b e t w e e n t h e c e n t e r s o f p r o b e p o i n t s a n d p r o b e s p a c i n g. A n y r e l a t i o n s h i p s u c h as t h i s w i l l d e p e n d to s o m e e x t e n t o n s o i l c h a r a c t e r i s t i c s, e s p e c i a l l y p a r t i c l e size, w a t e r t a b l e c o n d i t i o n s, a n d t h e a m p l i t u d e a n d f r e q u e n c y o f t h e v i b r a t o r. A r e l a t i o n s h i p b e t w e e n a l l o w a b l e b e a r i n g p r e s s u r e to l i m i t s e t t l e m e n t s t o 25 m m a n d p r o b e s p a c i n g is g i v e n in Fig. 9. H e r e a g a i n it m u s t be r e a l i z e d t h a t for t h e s a m e r e a s o n s s u c h a r e l a t i o n s h i p is s u i t a b l e o n l y f o r p r e l i m i n a r y d e s i g n. Fig. 9 S pacings o f Centers of Vibration-m A l l o w a b l e B e a r i n g P r e s s u r e as a F u n c t i o n of P r o b e S p a c i n g for F o o t i n g s H a v i n g W i d t h s V a r y i n g f r o m O n e t o T h r e e M e t e r s ( T h o r b u r n, 1975) L i k e b l a s t i n g, v i b r o c o m p a c t i o n c a n l o o s e n v e r y d e n s e z o n e s a n d b r e a k u p w e a k l y c e m e n t e d l a yers. A l t h o u g h t h e s t r e n g t h o f s u c h z o n e s w i l l t h e r e f o r e b e d e c r e a s e d, t h e y w i l l u s u a l l y s t i l l be s u f f i c i e n t l y d e n s e a n d s t r o n g f o r t h e p r o j e c t at h a n d. A l s o, as o b s e r v e d for s a n d s d e n s i f i e d by b l a s t i n g a n d b y h e a v y t a m p i n g, t h e p e n e t r a t i o n r e s i s t a n c e m a y i n c r e a s e w i t h t i m e a f t e r t r e a t m e n t, e v e n t h o u g h d e n s i f i c a t i o n a n d s u r f a c e s e t t l e m e n t a r e e s s e n t i a l l y c o m p l e t e a t t h e e n d o f t r e a t m e n t. E x p e r i e n c e at t h e K w i n a n a T e r m i n a l in W e s t e r n A u s t r a l i a ( C o n t r a c t i n g a n d C o n s t r u c t i o n E n g i n e e r, 1974) is a g o o d c a s e i n p o i n t. A t t h i s s i t e 1 2, v i b r o f l o t a t i o n p r o b e s w e r e m a d e f u l l d e p t h i n t o a s a n d d e p o s i t a b o u t 25 m t h i c k. C o n e p e n e t r a t i o n r e s i s t a n c e v a l u e s i n c r e a s e d b y 10 to 15 p e r c e n t o v e r t h e t h r e e w e e k s f o l l o w i n g t r e a t m e n t. W h e n c o a r s e s a n d s o r g r a v e l s a r e u s e d as b a c k fill m a t e r i a l s for v i b r o c o m p a c t i o n, t h e resulting p i l e s c a n a c t as d r a i n s b e c a u s e o f t h e i r h i g h h y d r a u l i c c o n d u c t i v i t y r e l a t i v e to the s u r r o u n d i n g sand. A s such, t h e y m a y s e r v e to d i s s i p a t e p o r e p r e s s u r e s f r o m p o t e n t i a l l y l i q u e - f i a b l e d e p o s i t s a n d t h e r e b y p r e v e n t l i q u e f a c t i o n. A m e t h o d for d e s i g n i n g g r a v e l d r a i n s y s t e m s for t h i s p u r p o s e is g i v e n by S e e d a n d B o o k e r (1977). It is i m p o r t a n t t o n o t e in s u c h s y s t e m s t h a t t h e u s e of d r a i n s to p r e v e n t l i q u e f a c t i o n u n d e r s e i s m i c l o a d i n g d o e s n o t e l i m i n a t e t h e p o t e n t i a l f o r s e t t l e m e n t. H e a v y T a m p i n g S o i l c o m p a c t i o n b y h e a v y t a m p i n g i n v o l v e s r e p e a t e d d r o p p i n g o f h e a v y w e i g h t s o n t o the g r o u n d s u r f a c e. T h e m e t h o d is a l s o t e r m e d d y n a m i c c o m p a c t i o n, d y n a m i c c o n s o l i d a t i o n, or p o u n d i n g. T h e t e c h n i q u e as d e v e l o p e d in its p r e s e n t f o r m for i m p r o v e m e n t o f l a r g e a r e a s to d e p t h s o f u p to 30 m w a s p i o n e e r e d b y M e n a r d (Menard, 1974; M e n a r d a n d B r o i s e, 1975). W h e n a p p l i e d to p a r t l y s a t u r a t e d soils, t h e d e n s i f i c a t i o n p r o c e s s is e s s e n t i a l l y t h e s a m e as t h a t for i m p a c t (Proctor) c o m p a c t i o n in t h e l a b o r a tory. In t h e c a s e of s a t u r a t e d c o h e s i o n l e s s s o i l s l i q u e f a c t i o n c a n be i n d u c e d, a n d t h e d e n s i f i c a t i o n p r o c e s s is s i m i l a r to t h a t a c c o m p a n y i n g b l a s t i n g a n d v i b r o c o m p a c t i o n. T h e e f f e c t i v e n e s s of t h e m e t h o d in s a t u r a t e d, f i n e g r a i n e d s o i l s is u n c e r t a i n ; b o t h s u c c e s s e s a n d f a i l u r e s h a v e b e e n r e p o r t e d. It w o u l d a p p e a r t h a t in s u c h m a t e r i a l s a b r e a k d o w n in t h e s o i l s t r u c t u r e, t h e g e n e r a t i o n o f e x c e s s p o r e w a t e r p r e s s u r e s, a n d t h e f o r m a t i o n o f d r a i n a g e c h a n n e l s b y f i s s u r i n g m a y b e r e q u i r e d. H e a v y t a m p i n g h a s b e e n e s p e c i a l l y e f f e c t i v e f o r c o m p a c t i o n o f w a s t e a n d r u b b l e fills. A m o n g r e c e n t r e f e r e n c e s w h i c h p r o v i d e d e t a i l s o f t h e m e t h o d a n d c a s e h i s t o r i e s a r e B h a n d a r i (1977), B o z k o e t al. (1976), C h a r l e s (1981), H a n s b o ( , 1978), K r u t o v e t al. (1978), L e o n a r d s e t al. (1980), L u k a s (1980), M é n a r d (1974), M e n a r d a n d B r o i s e (1975), M i n k o v e t al. (1980), Z h e n g e t al. (1980). T h e p o u n d e r s u s e d for h e a v y t a m p i n g m a y be c o n c r e t e b l o c k s, s t e e l p l a t e s, o r t h i c k s t e e l s h e l l s f i l l e d w i t h c o n c r e t e o r s a n d a n d m a y r a n g e f r o m o n e or t w o u p to 200 t o n s i n w e i g h t. D r o p h e i g h t s u p to 4 0 m h a v e b e e n u s e d. T h e p o u n d e r s a r e u s u a l l y s q u a r e o r c i r c u l a r in p l a n a n d h a v e d i m e n s i o n s o f u p to a f e w m e t e r s d e p e n d i n g o n w e i g h t r e q u i r e d, m a t e r i a l, a n d the d y n a m i c b e a r i n g c a p a c i t y at t h e s u r f a c e of the g r o u n d t o b e t r e a t e d. M o r e s t r e a m l i n e d s h a p e s h a v e b e e n u s e d for u n d e r w a t e r t a m p i n g. F o r l a r g e a r e a c o m p a c t i o n s e v e r a l r e p e t i t i o n s at p o i n t s s p a c e d s e v e r a l m e t e r s a p a r t in a g r i d p a t t e r n a r e a p p l i e d. A t y p i c a l t r e a t m e n t w i l l r e s u l t in a n a v e r a g e of 2 t o 3 b l o w s / m 2. A n i l l u s t r a t i o n o f a t y p i c a l g r i d p a t t e r n a n d r e p r e s e n t a t i v e e q u i p m e n t is s h o w n in Fig. 10. T w o o r t h r e e c o v e r a g e s o f a n a r e a m a y be r e q u i r e d, s e p a r a t e d b y t i m e i n t e r v a l s d e p e n d e n t on t h e r a t e o f d i s s i p a t i o n o f e x c e s s p o r e w a t e r p r e s s u r e a n d s t r e n g t h r e g a i n. T h e g e n e r a l r e s p o n s e of t h e g r o u n d as a f u n c t i o n o f t i m e a f t e r a c o v e r a g e is s h o w n in Fig. 11. T h e t i m e i n t e r v a l r e q u i r e d b e t w e e n c o v e r a g e s m a y r a n g e 517

10 Fig. 10 I l l u s t r a t i o n of H e a v y T a m p i n g (Î) A p p l i e d e n e r g y in t m / m 2 (2) V o l u m e v a r i a t i o n w i t h t i m e (3) R a t i o o f p o r e - p r e s s u r e t o i n i t i a l e f f e c t i v e s t r e s V a r i a t i o n of b e a r i n g c a p a c i t y f r o m d a y s for f r e e l y d r a i n i n g c o a r s e s a n d s to w e e k s for f i n e r - g r a i n e d soils. T h e g r o u n d s u r f a c e is u s u a l l y l e v e l l e d b e t w e e n c o v e r a g e s. T o i n s u r e u n i f o r m i t y a n d h i g h d e n s i t y in t h e n e a r s u r f a c e zone, s u r f a c e " i r o n i n g " is u sed. S m a l l i m p a c t s b y t h e p o u n d e r a r e m a d e o v e r t h e e n t i r e s u r f a c e. S u r f a c e s e t t l e m e n t s m a y b e f r o m t w o to f i v e p e r c e n t o f t h e t h i c k n e s s o f t h e z o n e b e i n g d e n s i f i e d p e r c o v e r a g e. Z h e n g e t al. (1980) d e t e r m i n e d t h e " e f f e c t i v e d e f o r m a t i o n, " d e f i n e d as t h e v o l u m e of c r a t e r l e s s t h e v o l u m e o f a d j a c e n t h e a v e f r o m d i s p l a c e d s oil, f o r s u c c e s s f u l d y n a m i c c o n s o l i d a t i o n of a s o f t t o m e d i u m s t i f f c l a y a n d a u n i f o r m f i n e s a n d. In t h e c l a y t h e d e f o r m a t i o n w a s 30 p e r c e n t e f f e c t i v e, a n d in t h e s a n d i t w a s 62 p e r c e n t e f f e c t i v e. W h e n h e a v y t a m p i n g is u s e d to p r e p a r e g r o u n d for s u p p o r t o f r e l a t i v e l y l i g h t (low rise) s t r u c t u r e s o n s h a l l o w f o u n d a t i o n s, t r e a t m e n t is s o m e t i m e s m a d e o n l y at f o o t i n g l o c a t i o n s. T h i s c a n b e an e c o n o m i c a l a n d e f f e c t i v e m e a n s f o r m i n i m i z i n g t o t a l a n d d i f f e r e n t i a l s e t t l e m e n t s. Of p a r t i c u l a r i n t e r e s t w h e n t h i s m e t h o d is b e i n g c o n s i d e r e d a r e t h e d e p t h of i n f l u e n c e a n d the l e v e l of p r o p e r t y i m p r o v e m e n t t h a t m a y b e T i m e b e t w e e n p a s s e s v a r i e s f r o m o n e to f o u r w e e k s a c c o r d i n g t o t h e s o i l type. Fig. 11 a c h i e v e d. t h a t w h e r e G r o u n d R e s p o n s e w i t h T i m e A f t e r S u c c e s s i v e C o v e r a g e s o f D y n a m i c C o n s o l i d a t i o n (Menard a n d B r o i s e, 1975) M e n a r d a n d B r o i s e (1975) p r o p o s e d D = /WH- (6) D = m a x i m u m d e p t h o f i n f l u e n c e, m W = f a l l i n g w e i g h t, m e t r i c t o n s H = h e i g h t of d r o p, m. L e o n a r d s e t al. (1980) a n a l y z e d s e v e n c a s e s a n d c o n c l u d e d D = 1/ 2 /WÌT (7) w a s m o r e a p p r o p r i a t e, a n d L u k a s (1980) c o n c l u d e d t h a t D = (0.65 to 0.80) /WÌT (8) 518

11 w a s b e s t s u i t e d for t h e e i g h t c a s e s s t u d i e d b y him. C l e a r l y, t h e d e p t h of i n f l u e n c e s h o u l d d e p e n d on f a c t o r s in a d d i t i o n t o t h e i m p a c t e n e r g y. S o i l t y p e m i g h t be e x p e c t e d to b e t h e m o s t i m p o r t a n t. A c r a n e d r o p is l e s s e f f i c i e n t t h a n a f r e e d r o p. T h e p r e s e n c e o f s o f t l a y e r s h a s a d a m p i n g i n f l u e n c e o n the d y n a m i c f o r c e s. D e f i n i t i o n of d e p t h o f i n f l u e n c e is i t s e l f s u b j e c t i v e a n d d e p e n d s b o t h o n t h e m e t h o d of m e a s u r e m e n t a n d t h e e n g i n e e r ' s d e f i n i t i o n o f w h a t c o n s t i t u t e s a m e a s u r a b l e g r o u n d i m p r o v e m e n t. W i t h i n a h o m o g e n e o u s s o i l l a y e r t h e a m o u n t o f g r o u n d i m p r o v e m e n t d e c r e a s e s w i t h d e p t h as shown, f o r e x a m p l e, b y Fig. 12. FRENCH RIVERA AIRPORT IN NICE IMPROVEMENT OF THE RECLAIMED LAND FOR THE PROPOSED NEW RUN-WAY r e s u l t s of h e a v y t a m p i n g o n s o i l s r a n g i n g f r o m s i l t s to c l e a n s a n d s to r u b b l e fills. T h e p o i n t r e f e r e n c e d to G u y o t a n d V a r a k s i n (1980) is f o r a s t r i p m i n e d w a s t e p i l e o f c l a y, s i l t y c l a y, s a n d y c l a y, a n d b o u l d e r s o f l i m e s t o n e a n d shale. F r o m t h e s e r e s u l t s it a p p e a r s t h a t the u s e o f e q u a t i o n (7) w o u l d p r o v i d e a c o n s e r v a t i v e e s t i m a t e of t h e e f f e c t i v e d e p t h of d y n a m i c c o m p a c t i o n a c h i e v e d, in m o s t cases. T h e a m o u n t o f s o i l i m p r o v e m e n t t h a t d e v e l o p s in a n y c a s e d e p e n d s o n s o i l t ype, w a t e r c o n d i t i o n s, a n d i n p u t e n e r g y p e r u n i t a rea. F i n e r - g r a i n e d s o i l s c a n n o t b e s t r e n g t h e n e d to t h e s a m e l e v e l as c a n c o a r s e r m a t e r i a l s. S o f t l a y e r s o f c l a y a n d p e a t i n h i b i t h i g h c o m p a c t i o n o f a d j a c e n t c o h e s i o n l e s s m a t e r i a l b e c a u s e o f t h e i r f l e x i b i l i t y. A r e v i e w of a v a i l a b l e c a s e s s u g g e s t s t h a t t h e r e m a y b e a d e f i n a b l e m a x i m u m l e v e l of i m p r o v e m e n t. L e o n a r d s et al. (1980) s u g g e s t t h a t t h i s l e v e l m a y b e a c o n e p e n e t r a t i o n r e s i s t a n c e o f a b o u t 150 k g / c m 2. A s t u d y o f t h e d a t a a s s o c i a t e d w i t h t h e c a s e s p l o t t e d in Fig. 13 s h o w s m a x i m u m v a l u e s of c o n e p e n e t r a t i o n r e s i s t a n c e o f 180 k g / c m 2, s t a n d a r d p e n e t r a t i o n r e s i s t a n c e o f 45 b l o w s / 0. 3 m, p r e s s u r e m e t e r l i m i t p r e s s u r e o f 3 MPa, a n d p r e s s u r e m e t e r m o d u l u s o f 25 M P a for c l e a n s a n d s. F i n e r - g r a i n e d m o r e c o m p r e s s i b l e s o i l s m a y h a v e m a x i m u m v a l u e s t h a t a r e less t h a n h a l f o f t h e s e. V a l u e s d e c r e a s e f r o m a m a x i m u m n e a r t h e g r o u n d s u r f a c e t o t h e o r i g i n a l i n - s i t u v a l u e at d e p t h D. A n a d d i t i o n a l c o n c e r n r e l a t i v e to h e a v y t a m p i n g, a n d b l a s t i n g as w e l l, is w h e t h e r d a m a g e m a y o c c u r t o f a c i l i t i e s l o c a t e d b e y o n d t h e e d g e s o f t h e a r e a b e i n g d e n s i f i e d b e c a u s e of t h e l a r g e i m p a c t e n e r g i e s. M e a s u r e m e n t s of v i b r a t i o n f r e q u e n c i e s h a v e g i v e n v a l u e s in t h e r a n g e of Hz. P a r t i c l e v e l o c i t y is r e l a t e d t o s c a l e d e n e r g y f a c t o r in Fig. 14. T h e l i n e s for w e t sand, d r y sand, a n d c l a y w e r e g i v e n b y W i s s (1967) f o r p r e d i c t i o n of p a r t i c l e v e l o c i t i e s r e s u l t i n g f r o m p i l e d r i v i n g o p e r a t i o n s. T h e l i n e for b u i l d i n g r u b b l e ( c o n s t r u c t i o n debris) c o m p a c t i o n b y h e a v y t a m p i n g w a s d e v e l o p e d by L u k a s (1980), a n d t h e a d d i t i o n a l p o i n t s a r e for h e a v y t a m p i n g o f sand. T h e s e l a t t e r p o i n t s p l o t n e a r t h e l i n e f o r r u b b l e a n d s u g g e s t t h a t a g i v e n s c a l e d e n e r g y p r o d u c e s a s o m e w h a t l o w e r p a r t i c l e v e l o c i t y t h a n t h e s a m e e n e r g y i n p u t b y p i l e d r i v i n g. Fig. 14 m a y b e u s e d t o e s t i m a t e t h e d i s t a n c e f r o m p o i n t of i m p a c t w h e r e d a m a g e c o u l d o c c u r. Fig. 12 o Before dynamic consolidation A fte r 3 passes of dynamic consolidation (each pass consists of 6 blows of a 170 ton hammer falling from 23 m) V a r i a t i o n in P r e s s u r e m e t e r M o d u l u s a n d L i m i t P r e s s u r e w i t h D e p t h a t N i c e A i r p o r t ( C o u r t e s y M. G a m b i n, T e c h n i q u e s L o u i s Menard) A n u m b e r o f f i e l d e x p e r i e n c e s h a v e b e e n s u m m a r i z e d in Fig. 13. B e c a u s e c o n s i d e r a b l e j u d g m e n t w a s r e q u i r e d in a s s e s s i n g t h e d e p t h o f g r o u n d i m p r o v e m e n t in a n u m b e r of c a s e s a n d b e c a u s e d i f f e r e n t m e t h o d s f o r e v a l u a t i n g i m p r o v e m e n t w e r e u s e d o n d i f f e r e n t p r o j e c t s, t h e d a t a in Fig. 13 a r e n o t p r e c i s e. N o n e t h e l e s s, t h e t r e n d is c l e a r. T h e p l o t t e d p o i n t s r e p r e s e n t the P r o g r e s s i v e L i q u e f a c t i o n In m a n y c a s e s t h e v o l u m e o f s o i l d e n s i f i e d by d e e p c o m p a c t i o n lies w i t h i n a p o t e n t i a l l y l i q u e - f i a b l e d e p o s i t o f m u c h l a r g e r a r e a l e x t e n t. T h e q u e s t i o n a r i s e s t h e n c o n c e r n i n g w h e t h e r, if in a n e a r t h q u a k e t h e s u r r o u n d i n g s o i l l i q u e f i e s, t h e r e w i l l b e t h e p o s s i b i l i t y of loss of s t a b i l i t y in t h e d e n s i f i e d z one. C o n c e i v a b l y, the d e v e l o p m e n t o f h i g h p o r e p r e s s u r e s i n t h e l i q u e f i e d z o n e c o u l d g e n e r a t e h i g h e r p o r e p r e s s u r e s in t h e d e n s i f i e d z o n e w i t h c o n s e q u e n t l o s s of s t r e n g t h. T o g u a r d a g a i n s t t h i s p o s s i b i l i t y it s h o u l d be s u f f i c i e n t t o e x t e n d t h e z o n e o f soil i m p r o v e m e n t l a t e r a l l y o u t w a r d f r o m t h e r e q u i r e d f o u n d a t i o n a r e a a d i s t a n c e e q u a l to t h e t h i c k n e s s o f t h e l a y e r b e i n g d e n s i f i e d. M o r e p r e c i s e e v a l u a t i o n s c a n be m a d e u s i n g a c o m p u t e r a n a l y s i s o f p o r e p r e s s u r e g e n e r a t i o n f o r t h e g i v e n c o n d i t i o n s as d e s c r i b e d b y B o o k e r et a l. (1976). A l t e r n a t i v e l y, t h e m e t h o d p r o p o s e d by 519

12 30 _ Predominontly cohesionless soil O Silty soils, fills, rubble f Full depth o f improved zone not determined / 0) O c Q) 3 CL <D O References Leonards et al. (1980) Bhandari (1977) Gambin (1979) Gam bin (1979)-Personal Comm Guyot and Varaksin (1980) Varaksin (1980) Jullié (1978) Minkov et al. (1980) Lukas (1980) _ v/energy/drop - ( t- m ) 1^ Fig. 13 D e p t h o f I n f l u e n c e as a F u n c t i o n o f I m p a c t E n e r g y for H e a v y T a m p i n g N a n d a k u m a r a n e t al. (1977), w h i c h a p p e a r s q u i t e c o n s e r v a t i v e, m i g h t b e c o n s i d e r e d. T i m e E f f e c t s M o r e a n d m o r e e v i d e n c e is b e c o m i n g a v a i l a b l e to i n d i c a t e t h a t in m a n y s a n d s t i m e - d e p e n d e n t i n c r e a s e s in s t r e n g t h a n d d e c r e a s e s in c o m p r e s s i b i l i t y d e v e l o p a f t e r d e n s i f i c a t i o n b y a n y o f t h e d e e p c o m p a c t i o n m e t h o d s. B e c a u s e t h e s e e f f e c t s c o n t i n u e o v e r p e r i o d s o f m a n y w e e k s o r m o n t h s, t h e y c a n n o t b e e x p l a i n e d in t e r m s o f p o r e p r e s s u r e d i s s i p a t i o n, w h i c h c o n t i n u e s o n l y f o r p e r i o d s o f s e v e r a l m i n u t e s a t t h e m o s t in t h e c a s e o f c l e a n sand. T h e a g i n g e f f e c t h a s b e e n s h o w n to g i v e s u b s t a n t i a l i n c r e a s e in t h e s t r e n g t h o f s a n d s u n d e r c y c l i c l o a d i n g, as m a y be s e e n in Fig. 15. A l t h o u g h a n u m b e r o f h y p o t h e s e s h a v e b e e n a d v a n c e d t o e x p l a i n t h i s b e h a v i o r ; e. g., t h i x o - t r o p i c h a r d e n i n g, c h e m i c a l c e m e n t a t i o n, t h e e f f e c t s of d i s s o l v e d g a s e s, t h e m e c h a n i s m is n o t y e t c o m p l e t e l y c l e a r. F r o m a p r a c t i c a l s t a n d p o i n t, h o w e v e r, it w o u l d be r e a s o n a b l e to c o n c l u d e t h a t e v a l u a t i o n s o f t h e g r o u n d s h o r t l y a f t e r t h e c o m p l e t i o n o f d e e p d e n s i f i c a t i o n w i l l g i v e c o n s e r v a t i v e r e s u l t s. S O I L I M P R O V E M E N T B Y P R E C O M P R E S S I O N I n t r o d u c t i o n T h e s t r e n g t h e n i n g a n d p r e c o n s o l i d a t i o n o f w e a k a n d c o m p r e s s i b l e s o i l s b y p r e l o a d i n g p r i o r to c o n s t r u c t i o n is o n e of t h e o l d e s t a n d m o s t w i d e l y u s e d m e t h o d s for s o i l i m p r o v e m e n t. It is p a r t i c u l a r l y w e l l - s u i t e d for u s e w i t h s o i l s t h a t u n d e r g o l a r g e v o l u m e d e c r e a s e s a n d s t r e n g t h i n c r e a s e s u n d e r s u s t a i n e d s t a t i c l o a d s a n d w h e n t h e r e is s u f f i c i e n t t i m e a v a i l a b l e f o r t h e r e q u i r e d c o m p r e s s i o n s t o o c c u r. S u r c h a r g e loads; i.e., l o a d s in e x c e s s o f t h o s e to be a p p l i e d b y a p e r m a n e n t fill o r s t r u c t u r e c a n be u s e d to a c c e l e r a t e t h e p r o c e s s. W h e n t h e a n t i c i p a t e d t i m e f o r c o m p r e s s i o n is e x c e s s i v e, v e r t i c a l d r a i n s m a y be u s e d t o s h o r t e n t h e t i m e r e q u i r e d p r o v i d e d t h e c o m p r e s s i o n is o f t h e p r i m a r y c o n s o l i d a t i o n type. T h e s o i l t y p e s b e s t s u i t e d for 520

13 Fig. 14 O Gigan (1977) a Leonards, et al. (1980) Lukas (1980) i i i r i itrr P la ste r cracks (residences) I - Recom m ended sa fe level (re s id e n c e s ) i ild i ng ble v/energy (ft-lbs)/ Distance (ft) P a r t i c l e V e l o c i t y as a S c a l e d E n e r g y F a c t o r Seed (1979) Disturbing. Unpleasant i W ell noticea ble : Perceptible : Im perceptible L ab orato ry te s t d ata - Monterey No. 0 sand - A H ydraulic sand fill from Lower San Fernando Dorn O H ydraulic sand fill from Upper San Fernando Dam South Texas sand V San Mateo sond B anerjee e to l. (1979) (qtjcs 14 kg/cm, K»I.O, 0^=87%) _ Q In itia l liquefa ctio n in 10 cycles O ± 5 % axial s tra in in 10 cycles F u n c t i o n of Tim e after D eposition-years i r f u l l y t o i m p r o v e t h e f o u n d a t i o n s o i l s for b u i l d ings, e m b a n k m e n t s, h i g h w a y s, r u n w a y s, t a n k s, a n d a b u t m e n t s. S e v e r a l r e c e n t c o m p r e h e n s i v e t r e a t m e n t s of p r e c o m p r e s s i o n a n d t o p i c s r e l a t e d to its a p p l i c a tion, w i t h a n d w i t h o u t d r a i n s, a r e a v a i l a b l e, i n c l u d i n g t h o s e b y J o h n s o n (1970a, b ), B j e r r u m (1972), U.S. N a v y (1971), P i l o t (1977), S c h l o s s e r a n d J u r a n (1979), A k a g i (1977, 1979), H a n s b o (1979). T h e s t a t e - o f - t h e - a r t b y P i l o t (1977) is e s p e c i a l l y c o m p l e t e a n d w e d o c u m e n t e d a n d c o n t a i n s a n e x t e n s i v e l i s t o f c a s e h i s t o r i e s. B e c a u s e o f t h e s e r e f e r e n c e s, d e t a i l e d t r e a t m e n t of a l l t o p i c s i m p o r t a n t to p r e c o m p r e s s i o n is n o t g i v e n h e r e. E m p h a s i s is on r e c e n t d e v e l o p m e n t s a n d p r a c t i c a l c o n s i d e r a t i o n s t h a t i n f l u e n c e d e s i g n a n d p e r f o r m a n c e o f p r e c o m p r e s s i o n s y s t e m s. T y p e s o f P r e l o a d s A l t h o u g h e a r t h f i l l s a r e t h e m o s t c o m m o n l y u s e d t y p e of p r e l o a d, a n y s y s t e m t h a t l e a d s to d r a i n a g e o f p o r e w a t e r a n d c o m p r e s s i o n o f t h e s o i l m a y b e s u i t a b l e. W a t e r in t a n k s h a s b e e n u s e d t o p r e l o a d s m a l l a r e a s, a n d w a t e r in l i n e d p o n d s c a n b e u s e d to p r e l o a d l a r g e r a r e a s. V a c u u m p r e l o a d i n g b y p u m p i n g f r o m b e n e a t h a n i m p e r v i o u s m e m b r a n e p l a c e d o v e r t h e g r o u n d s u r f a c e c a n p r o d u c e s u r c h a r g e l o a d s u p to 60 t o 80 k P a (Holtz a n d W a g e r, 1975; P i l o t, 1977). A n c h o r a n d j a c k s y s t e m s c a n b e d e v i s e d f o r s p e c i a l c a s e s. G r o u n d w a t e r l o w e r i n g p r o v i d e s a n i n c r e a s e in c o n s o l i d a t i o n p r e s s u r e e q u a l to t h e u n i t w e i g h t o f w a t e r t i m e s the d r a w d o w n d i s t a n c e. C o n s o l i d a t i o n b y e l e c t r o - o s m o s i s is t h e s a m e in m a n y r e s p e c t s as c o n s o l i d a t i o n u n d e r e x t e r n a l l y a p p l i e d s t r e s s e s, e x c e p t t h a t t h e d r i v i n g f o r c e f o r d r a i n a g e is i n d u c e d i n t e r n a l l y b y an e l e c t r i c a l field. P r e l o a d i n g b y v a c u u m, w a t e r t a b l e l o w e r i n g, a n d e l e c t r o - o s m o s i s o f f e r t h e a d v a n t a g e s t h a t t h e r e a r e n o s t a b i l i t y p r o b l e m s, a n d l a r g e v o l u m e s of s u r c h a r g e fill a r e n o t r e q u i r e d. O n the o t h e r h a n d, t h e y a r e m o r e c o m p l e x in e x e c u t i o n t h a n t h e o t h e r m e t h o d s. T h e o r e t i c a l B a s i s for D e s i g n T h e u s u a l o b j e c t i v e of d e s i g n o f s u r c h a r g e l o a d s a n d d u r a t i o n o f t h e i r a p p l i c a t i o n is to r e d u c e t h e m a g n i t u d e of s e t t l e m e n t a f t e r c o n s t r u c t i o n. S e t t l e m e n t a t a n y t i m e m a y b e e x p r e s s e d as s. + i Us + co n s (9) o * 10 10* 10 Fig. 15 T im e o f te r D e p o s itio n -d a y s I n f l u e n c e of P e r i o d o f S u s t a i n e d P r e s s u r e o n S t r e s s R a t i o C a u s i n g P e a k C y c l i c P o r e P r e s s u r e R a t i o o f 100% i m p r o v e m e n t b y p r e c o m p r e s s i o n a r e s a t u r a t e d s o f t c l a y s, c o m p r e s s i b l e silts, o r g a n i c c l a y s, a n d p e a t s. V e r t i c a l d r a i n s a r e o f g r e a t e s t e f f e c t i v e n e s s in i n o r g a n i c c l a y s a n d s i l t s t h a t e x h i b i t l i t t l e s e c o n d a r y c o m p r e s s i o n. P r e l o a d i n g a n d p r e c o m p r e s s i o n h a v e b e e n u s e d s u c c e s s - in w h i c h s^ s e t t l e m e n t at t i m e t c o n s = i m m e d i a t e s e t t l e m e n t (from gas c o m p r e s s i o n, s h e a r d i s t o r t i o n ) = a v e r a g e d e g r e e o f c o n s o l i d a t i o n = f i n a l c o n s o l i d a t i o n s e t t l e m e n t = s e c o n d a r y c o m p r e s s i o n s e t t l e m e n t. T h e o b j e c t i v e m a y b e e i t h e r : (1) to d e t e r m i n e t h e m a g n i t u d e of s u r c h a r g e p r e s s u r e (ps ) r e q u i r e d t o i n s u r e t h a t t h e t o t a l s e t t l e m e n t ' ' f> 521

14 be c o m p l e t e in a g i v e n l e n g t h o f t ime, o r (2) to d e t e r m i n e t h e l e n g t h o f t i m e r e q u i r e d to a c h i e v e a g i v e n a m o u n t o f s e t t l e m e n t u n d e r a g i v e n s u r c h a r g e load. It is c o n v e n i e n t to c o n s i d e r p r i m a r y c o n s o l i d a t i o n a n d s e c o n d a r y c o m p r e s s i o n as s e p a r a t e p h a s e s, e v e n t h o u g h b o t h t y p e s o f v o l u m e c h a n g e m a y b e i n p r o g r e s s c o n c u r r e n t l y. If t h e t i m e o f l o a d i n g is s h o r t r e l a t i v e to t h e t o t a l c o n s o l i d a t i o n p e r i o d, t h e n t h e a s s u m p t i o n o f i n s t a n t a n e o u s a p p l i c a t i o n o f t h e t o t a l l o a d at t h e e n d of o n e h a l f t h e l o a d i n g p e r i o d w i l l n o t l e a d to s e r i o u s e r r o r. If not, t h e n m o r e e x a c t a n a l y s e s m a y b e m a d e. C o n s o l i d a t i o n s e t t l e m e n t e s t i m a t e s for p e r m a n e n t f i l l a n d s t r u c t u r e l o a d s a r e m a d e in t h e u s u a l w a y. In t h o s e c a s e s w h e r e s o i l p r o p e r t i e s a n d / o r s t r e s s c o n d i t i o n s v a r y w i t h d e p t h, it m a y be n e c e s s a r y to a n a l y z e t h e p r o f i l e as a s e r i e s of s u b l a y e r s. T h e t i m e r a t e o f s e t t l e m e n t f o r p r i m a r y c o n s o l i d a t i o n in o n e d i m e n s i o n m a y b e d e t e r m i n e d u s i n g t h e c l a s s i c a l T e r z a g h i t h e o r y. In t h o s e c a s e s w h e r e t h e s t r a i n p r o f i l e w i t h d e p t h is n o t e s s e n t i a l l y c o n s t a n t, as a s s u m e d in t h e T e r z a g h i s o l u t i o n, a n o n - l i n e a r s t r e s s - s t r a i n m e t h o d, s u c h as t h a t p r e s e n t e d b y D u n c a n a n d B u c h i g n a n i (1976) b a s e d o n J a n b u (1965) m a y g i v e b e t t e r r e s u l t s. T h e e f f e c t of d e c r e a s i n g v e r t i c a l s t r a i n s w i t h d e p t h is t o i n c r e a s e t h e r a t e of s e t t l e m e n t c o m p a r e d t o t h e T e r z a g h i s o l u t i o n. T h e s t r e s s vs. t i m e a n d s e t t l e m e n t vs. t i m e r e l a t i o n s h i p s for a s o i l l a y e r u n d e r s t r e s s i n c r e a s e p f w o u l d b e as s h o w n in Fig. 16 in the a b s e n c e of s e c o n d a r y c o m p r e s s i o n. i n d e f i n i t e l y, t h e n a t i m e - s e t t l e m e n t c u r v e c o u l d b e o b t a i n e d in t h e s a m e w a y a n d p l o t t e d as s h o w n b y t h e l o w e r c u r v e in Fig. 16. If t h e s u r c h a r g e w e r e l e f t in p l a c e u n t i l t i m e tgr, t h e n the l a y e r w i l l h a v e s e t t l e d an a m o u n t e q u a l to t h a t t o b e e x p e c t e d u n d e r t h e p e r m a n e n t f i l l alone; i.e., s tr 3f. A t t h i s t i m e t h e l a y e r w i l l h a v e r e a c h e d a n a v e r a g e d e g r e e of c o n s o l i d a t i o n Û S R g i v e n b y U S R s f+s ( 1 0 ) A s p o i n t e d o u t b y A l d r i c h (1965) a n d e x t e n d e d b y J o h n s o n (1970a) t h e d i s t r i b u t i o n of e f f e c t i v e a n d e x c e s s p o r e w a t e r p r e s s u r e s b e f o r e a n d a f t e r s u r c h a r g e r e m o v a l w i l l b e as s h o w n in Fig. 17 f o r a c l a y l a y e r d r a i n e d at b o t h b o u n d a r i e s. T h u s, a s u b s t a n t i a l p o r t i o n o f t h e l a y e r m a y u n d e r g o f u r t h e r c o n s o l i d a t i o n a f t e r r e m o v a l of t h e s u r c h a r g e load, w h e r e a s t h e r e m a i n d e r w i l l b e u n l o a d e d. A l t h o u g h t h e u n l o a d i n g o f t h e z o n e s n e a r d r a i n a g e b o u n d a r i e s w i l l g e n e r a l l y n o t l e a d to s i g n i f i c a n t h e a v e, t h e a d d i t i o n a l c o n s o l i d a t i o n in t h e c e n t r a l p o r t i o n m a y b e i m p o r t a n t. If a s u r c h a r g e l o a d t h a t a p p l i e d an a d d i t i o n a l s t r e s s p s w e r e a l s o u s e d a n d l e f t in p l a c e (1) Pore pressure distribution ot t corresponding to USR (2) Pore pressure distribution required to prevent fu rth e r settlem ent if ps removed Fig. 17 P o r e P r e s s u r e D i s t r i b u t i o n a f t e r R e m o v a l o f S u r c h a r g e L o a d a t T i m e fcsr T o e l i m i n a t e f u r t h e r p r i m a r y c o n s o l i d a t i o n f o l l o w i n g t h e r e m o v a l of t h e s u r c h a r g e, t h e s u r c h a r g e s h o u l d b e l e f t in p l a c e u n t i l t h e p o r e p r e s s u r e a t t h e m o s t c r i t i c a l p o i n t ; i.e., t h e p o i n t t h a t is l a s t to c o n s o l i d a t e, h a s i t s e l f r e a c h e d a c o n s o l i d a t i o n r a t i o U z g i v e n b y Fig. 16 C o m p e n s a t i o n for P r i m a r y C o m p r e s s i o n U s i n g S u r c h a r g e L o a d i n g < v f+s >f + Ps (11) 522

15 T i m e s c o r r e s p o n d i n g to U S R a n d U z a r e f o u n d u s i n g the T e r z a g h i t h e o r y a n d t h e c o e f f i c i e n t of c o n s o l i d a t i o n c ^ a c c o r d i n g to w h e r e T is t h e a p p r o p r i a t e v a l u e o f d i m e n s i o n - le s s t i m e f a c t o r. B e c a u s e t h i s a p p r o a c h r e q u i r e s t h a t t h e s u r c h a r g e be l e f t in p l a c e u n t i l all p o i n t s a r e f u l l y c o n s o l i d a t e d u n d e r p^, o v e r c o n s o l i d a t i o n w i l l d e v e l o p in m o s t o f t h e s o i l layer. T h u s it is c o n s e r v a t i v e, a n d t h e a c t u a l p r e c o m p r e s s i o n s e t t l e m e n t w i l l b e s i g n i f i c a n t l y g r e a t e r t h a n Sj. A f u r t h e r c o m p l i c a t i n g f a c t o r a r i s e s i n t h a t e q u a t i o n (11) is s t r e s s - b a s e d ; w h e r e a s c v is u s u a l l y d e t e r m i n e d u s i n g a s t r a i n - b a s e d p r o c e d u r e. A s t h e s t r e s s - s t r a i n b e h a v i o r o f t h e s o i l is n o n - l i n e a r, t h e r e is s o m e u n c e r t a i n t y in the p r e d i c t e d t i m e s a n d s u r c h a r g e l o a d s r e q u i r e d. T h i s p r o b l e m is p r e s e n t l y u n d e r s t u d y at t h e U n i v e r s i t y o f C a l i f o r n i a, B e r k e l e y, a n d p r e l i m i n a r y i n d i c a t i o n s a r e t h a t in its p r e s e n t f o r m t h e m e t h o d g i v e s c o n s e r v a t i v e r e s u l t s ; i.e., h i g h e r v a l u e s o f p g o r t i m e o f s u r c h a r g i n g a r e p r e d i c t e d t h a n a c t u a l l y r e q u i r e d. Vertical Drains In m a n y c a s e s t h e t i m e r e q u i r e d f o r s u r c h a r g i n g is e x c e s s i v e, t h e s u r c h a r g e r e q u i r e d f o r the t i m e a v a i l a b l e is t o o g r e a t, o r t h e r a t e of s t r e n g t h g a i n is t o o s l o w to p e r m i t r a p i d fill p l a c e m e n t. F o r s o i l s w h o s e c o m p r e s s i o n is d o m i n a t e d b y p r i m a r y c o n s o l i d a t i o n, v e r t i c a l d r a i n s m a y b e u s e d to a c c e l e r a t e t h e r a t e o f s e t t l e m e n t, b e c a u s e c o n s o l i d a t i o n t i m e s v a r y as t h e s q u a r e o f t h e d r a i n a g e p a t h l e n g t h, a n d b e c a u s e m o s t d e p o s i t s h a v e g r e a t e r p e r m e a b i l i t y in t h e h o r i z o n t a l t h a n in t h e v e r t i c a l d i r e c t i o n. A s c h e m a t i c d i a g r a m of a t y p i c a l v e r t i c a l d r a i n i n s t a l l a t i o n is s h o w n in Fig. 18. V e r t i c a l d r a i n s a r e i n e f f e c t i v e i n p e a t s, o r g a n i c c l a y s, a n d o t h e r s o i l s w h o s e s e t t l e m e n t b e h a v i o r is d o m i n a t e d by s e c o n d a r y c o m p r e s s i o n. serricve* r >i a t c O r FILL OfBUA\iHr fui S e c o n d a r y c o m p r e s s i o n m a y r e p r e s e n t a v e r y s i g n i f i c a n t p o r t i o n or the t o t a l c o m p r e s s i o n of s o m e soils, e s p e c i a l l y o r g a n i c c l a y s a n d p e a t s. P r e c o m p r e s s i o n u s i n g s u r c h a r g e l o a d i n g s m a y be e f f e c t i v e f o r m i n i m i z i n g t h e e f f e c t s of s u b s e q u e n t s e c o n d a r y c o m p r e s s i o n u n d e r p e r m a n e n t loads. T h e c o n c e p t is t o e s t i m a t e t h e t o t a l s e t t l e m e n t u n d e r pj a s t h e s u m o f t h a t d u e to p r i m a r y c o n s o l i d a t i o n a n d t h a t d u e to s e c o n d a r y c o m p r e s s i o n, s s e c, a n t i c i p a t e d to o c c u r d u r i n g t h e l i f e of t h e s t r u c t u r e. s s e c is d e t e r m i n e d a c c o r d i n g to C H log (t/t ) a p ^ p (t > tp ) (13) r r r SA/VD DBA IN ' SA HO 0 a Iy in w h i c h C a is t h e v e r t i c a l s t r a i n p e r l o g c y c l e i n c r e a s e i n t i m e s u b s e q u e n t t o t h e e n d o f p r i m a r y c o n s o l i d a t i o n a t tp, a n d Hp is the l a y e r t h i c k n e s s a t t i m e t D. T h e a n a l o g o u s e q u a t i o n t o (11) f o r t h e c r i t i c a l p o i n t f o r t h i s c a s e is (Uz W s f + C a H P l o 9 (t/y s f+s (14) T h e n a t u r e of s e c o n d a r y c o m p r e s s i o n is s u c h t h a t s o m e t i m e a f t e r s u r c h a r g e p s is r e m o v e d, s e c o n d a r y c o m p r e s s i o n w i l l r e a p p e a r u n d e r Pf. T h i s e f f e c t is s m a l l, h o w e v e r, a n d c a n u s u a l l y be n e g l e c t e d (Johnson, a ). T h e i n c r e a s e in u n d r a i n e d s h e a r s t r e n g t h w h i c h a c c o m p a n i e s p r e l o a d i n g m a y be t h e m o s t i m p o r t a n t e f f e c t in m a n y c a s e s. T h e u n d r a i n e d s t r e n g t h a f t e r a g i v e n d u r a t i o n o f p r e l o a d i n g m a y b e e s t i m a t e d u s i n g t h e p r i n c i p l e s of t h e S H A N S E P p r o c e d u r e (Ladd a n d F o o t t, 1974) t o g e t h e r w i t h an a n a l y s i s t o e s t i m a t e t h e i n c r e a s e in e f f e c t i v e c o n s o l i d a t i o n p r e s s u r e s w i t h i n t h e p r e l o a d e d l a yers. Fig. 18 T y p i c a l V e r t i c a l D r a i n I n s t a l l a t i o n T h e t h e o r y for c o n s o l i d a t i o n b y r a d i a l d r a i n a g e a n d b y c o m b i n e d r a d i a l a n d v e r t i c a l d r a i n a g e is w e l l d e v e l o p e d (Barron, 1948; C a r i l l o, 1942). T h e r e s u l t s a r e s u m m a r i z e d in Figs. 19 a n d 20. It is i m p o r t a n t t o n o t e t h a t d r a i n s p a c i n g is a f a r m o r e s i g n i f i c a n t p a r a m e t e r in t h e d e t e r m i n a t i o n of c o n s o l i d a t i o n t i m e t h a n is d r a i n diameter. O l s o n e t al. (1974) h a v e d e v e l o p e d a f i n i t e d i f f e r e n c e c o m p u t e r p r o g r a m t h a t c a n b e u s e d to i n v e s t i g a t e the e f f e c t s of t i m e - d e p e n d e n t l o a d ing, v a r i a b l e c o n s o l i d a t i o n c o e f f i c i e n t s, n o n l i n e a r s o i l s t r e s s - s t r a i n b e h a v i o r, t h e i n f l u e n c e s o f l a r g e s t r a i n s, a n d t h e i n s t a l l a t i o n of d r a i n s a f t e r o n e - d i m e n s i o n a l s e t t l e m e n t has b e g u n. U n t i l a f e w y e a r s a g o v e r t i c a l d r a i n s of sand, t y p i c a l l y 200 t o 500 m m in d i a m e t e r a n d s p a c e d a n y w h e r e f r o m 1.5 to 6.0 m o n c e n t e r s, w e r e w i d e l y u sed. I n s t a l l a t i o n w a s a c c o m p l i s h e d u s i n g a v a r i e t y o f t e c h n i q u e s o f b o t h the d i s p l a c e m e n t a n d n o n - d i s p l a c e m e n t t ype. D i s p l a c e m e n t d r a i n s, w h i l e g e n e r a l l y l e s s e x p e n s i v e a n d f a s t e r to 523

16 i n s t a l l, c a n d i s t u r b t h e s u r r o u n d i n g s o i l s. T h e r e s u l t i n g "smear" z o n e c a n i m p e d e d r a i n a g e, a n d t h e d i s t u r b e d s o i l m a y b e w e a k e n e d. T h e s e e f f e c t s m a y n o t be a s d e t r i m e n t a l as e a r l i e r b e l i e v e d, h o w e v e r, o w i n g to t h e p o s s i b i l i t i e s of (1) r e c o n s o l i d a t i o n to a h i g h e r s t r e n g t h t h a n t h e o r i g i n a l, a n d (2) t h e o p e n i n g o f c r a c k s a n d f i s s u r e s t h a t f i l l w i t h s a n d d u r i n g i n s t a l l a t i o n a n d t h e r e b y i n c r e a s e t h e e f f e c t i v e d r a i n a g e a rea. A k a g i (1977, 1979) c o n c l u d e d t h a t r e l i a b l e d a t a a r e l a c k i n g to e s t a b l i s h w h e t h e r n o n - d i s p l a c e m e n t d r a i n s a r e i n d e e d m o r e e f f e c t i v e t h a n t h e d i s p l a c e m e n t type. VERTICAL CONSOLIDATION: k, 1 e0i H 'T, RADIAL CONSOLIDATION: V - 'o' deth av-vrk I OR OR COMBINED RADIAL AND VERTICAL FLOW A T ANY TIME: EXCESS PORE WATER PRESSURE ) RATIOS DECREE OF CONSOLIDATION Fig. 19 U I U.1- A T A POINT AVERAGE VALUE I I t <m i AT A POINT AVERAGE VALUES S u m m a r y of C o n s o l i d a t i o n T h e o r y for V e r t i c a l D r a i n D e s i g n P r e s e n t i n d i c a t i o n s a r e t h a t c o n v e n t i o n a l s a n d d r a i n s i n s t a l l e d for t h e a c c e l e r a t i o n of c o n s o l i d a t i o n m a y s o o n be t h i n g s of t h e p a s t, as a v a r i e t y of p r e f a b r i c a t e d d r a i n s a r e c o m i n g i n t o w i d e use. B a n d - s h a p e d d r a i n s o f t h e o r d e r of 100 m m w i d e b y 1 to 7 m m t h i c k a r e p r o d u c e d by s e v e r a l m a n u f a c t u r e r s. T h e s e d r a i n s c a n be r a p i d l y i n s t a l l e d t o d e p t h s u p to 50 m b y m a c h i n e s w i t h s p e c i a l m a n d r e l s. D r a i n s p a c i n g s o f t h e o r d e r of 1 m a r e t y p i c a l. B o t h d y n a m i c a n d s t a t i c m e t h o d s o f i n s t a l l a t i o n a r e u s e d. C i r c u l a r p r e f a b r i c a t e d d r a i n s o r w i c k s c o m p o s e d o f s a n d w i t h i n c y l i n d r i c a l f a b r i c c o n t a i n e r s a r e a l s o used. A d e t a i l e d d i s c u s s i o n of t h e s e n e w d r a i n s, t h e i r s p e c i f i c f e a t u r e s, a n d m e t h o d s of i n s t a l l a t i o n is b e y o n d t h e s c o p e o f t h i s r e p o r t. H a n s b o (1979) h a s p r e s e n t e d a c o m p r e h e n s i v e o v e r v i e w of c o n s o l i d a t i o n u s i n g p r e f a b r i c a t e d b a n d - s h a p e d d r a i n s. O n l y a f e w g e n e r a l c h a r a c t e r i s t i c s a r e s u m m a r i z e d here. K j e l l m a n ' s c a r d b o a r d w i c k, i n t r o d u c e d in 1937, w a s t h e f i r s t o f t h e p r e f a b r i c a t e d d r a i n s. P r e s e n t l y t h e r e a r e s e v e r a l t y p e s o n t h e m a r k e t u n d e r s u c h n a m e s as A l i d r a i n, G e o d r a i n, C a s t l e B o a r d, C o l b o n d, M e b r a d r a i n, a n d P V C D r a i n. T h e d r a i n s u s u a l l y c o n s i s t o f a c o r e o f p l a s t i c a n d a f i l t e r s l e e v e of p a p e r, f i b r o u s m a t e r i a l, or p o r o u s p l a s t i c. T h e c r o s s s e c t i o n d e s i g n p r o v i d e s for a s y s t e m o f v e r t i c a l c h a n n e l s for w a t e r flow. T h e C o l b o n d D r a i n d i f f e r s f r o m the o t h e r s in t h a t it is a n o n - w o v e n f a b r i c t h r o u g h out, a n d it is s i g n i f i c a n t l y w i d e r (30 cm) t h a n t h e o t h e r s. T h e m a n d r e l s u s e d f o r d r a i n i n s t a l l a t i o n a r e of c r o s s s e c t i o n c o n s i d e r a b l y l a r g e r t h a n t h e d r a i n i t s e l f. Fig. 21 is a n e x a m p l e. T h u s i n s t a l l a t i o n o f t h e d r a i n n e c e s s a r i l y c a u s e s s o m e d i s t u r b a n c e of t h e s u r r o u n d i n g g r o u n d Time Factor, Tv and T r Fig. 20 C o n s o l i d a t i o n S o l u t i o n f o r Radial F l o w a n d E q u a l V e r t i c a l S t r a i n at G r o u n d S u r f a c e (Barron, 1948) Fig. 21 C r o s s S e c t i o n of a P l a s t i c D r a i n a n d M a n d r e l 524

17 T h e f i l t e r s l e e v e s u r r o u n d i n g t h e p l a s t i c c o r e m u s t s a t i s f y s e v e r a l c r i t e r i a : 1. Its p e r m e a b i l i t y s h o u l d n o t b e s i g n i f i c a n t l y l e s s t h a n t h a t o f t h e s u r r o u n d i n g soil. 2. F i n e s o i l p a r t i c l e s s h o u l d be r e t a i n e d to p r e v e n t c l o g g i n g of f l o w c h a n n e l s in the c o r e. 3. T h e f i l t e r s h o u l d b e s t i f f e n o u g h s o as n o t to b e p r e s s e d i n t o c o r e c h a n n e l s b y h i g h l a t e r a l s o i l p r e s s u r e s a n d s t r o n g e n o u g h n o t t o b e d a m a g e d d u r i n g i n s t a l lation. 4. T h e f i l t e r s h o u l d n o t u n d e r g o p h y s i c a l, c h e m i c a l, o r b i o l o g i c a l d e t e r i o r a t i o n d u r i n g t h e i n t e n d e d l i f e o f t h e d r a i n. T h e o r e t i c a l d e t e r m i n a t i o n o f r e q u i r e d d r a i n s p a c i n g c a n be m a d e in t h e s a m e w a y as for s a n d d r a i n s ; i.e., w i t h t h e a i d o f F igs. 19 a n d 20. A l t e r n a t i v e l y, if c o n s o l i d a t i o n d u e to v e r t i c a l f l o w is n e g l i g i b l e c o m p a r e d to t h a t d u e to r a d i a l flow, w h i c h is o f t e n t h e case, t h e n the t i m e of c o n s o l i d a t i o n t c a n be d e t e r m i n e d a c c o r d i n g to In 8c v - h 1 - U. (15) w h e r e is t h e a v e r a g e d e g r e e o f c o n s o l i d a t i o n. T h e p a r a m e t e r p is g i v e n, to a g o o d a p p r o x i m a tion, in t e r m s o f n ( = d e / d w ) b y y = In (n) (16) f o r t h e v a l u e s o f n (>12, e x c e p t f o r C o l b o n d, >8) a n d d r a i n s p a c i n g (>0.8 m) u s e d in p r a c t i c e. T h e e q u i v a l e n t d i a m e t e r dw o f a b a n d - s h a p e d d r a i n o f w i d t h b a n d t h i c k n e s s t is t a k e n as d = w 2 (b + t) (17) B o t h w e l l r e s i s t a n c e a n d d i s t u r b a n c e d u r i n g i n s t a l l a t i o n m a y c a u s e t h e a c t u a l t i m e s for c o n s o l i d a t i o n to b e g r e a t e r t h a n p r e d i c t e d b y Fig. 20 o r Eq. (15). B o t h of t h e s e c o n s i d e r a t i o n s a r e d i s c u s s e d b y H a n s b o (1979). P r e f a b r i c a t e d b a n d - s h a p e d d r a i n s c a n b e i n s t a l l e d a t o r i e n t a t i o n s o t h e r t h a n v e r t i c a l, w h i c h e n a b l e s t h e i r u s e for s p e c i a l a p p l i c a t i o n s s u c h as u n d e r - d r a i n a g e a n d o n s l o p e s. B e c a u s e t h e y c a n t o l e r a t e s i g n i f i c a n t d i s p l a c e m e n t s w i t h o u t r u p t u r e, p r e f a b r i c a t e d d r a i n s a r e n o t as s u s c e p t i b l e to loss of e f f e c t i v e n e s s d u e to s h e a r d i s p l a c e m e n t s as c a n o c c u r in t h e c a s e o f s a n d d r a i n s. S o m e P r a c t i c a l C o n s i d e r a t i o n s F o r p r e c o m p r e s s i o n w i t h o u t v e r t i c a l d r a i n s t h e r a t e o f c o n s o l i d a t i o n is c o n t r o l l e d by the c o e f f i c i e n t o f c o n s o l i d a t i o n for v e r t i c a l flow, c v _v. B o t h l a b o r a t o r y a n d f i e l d t e s t s m a y be u s e d for its d e t e r m i n a t i o n, a n d t h e r e is e x t e n s i v e l i t e r a t u r e o n t h e m e t h o d s, t h e i r a c c u r a c y a n d l i m i t a t i o n s. S e t t l e m e n t p r e d i c t i o n s f o r t w o - a n d t h r e e - d i m e n s i o n a l d e f o r m a t i o n s a n d d r a i n a g e c o n d i t i o n s a r e m o r e c o m p l e x t h a n t h e o n e - d i m e n s i o n a l p r o c e d u r e d e s c r i b e d h e r e i n. C o m p u t e r a n a l y s e s c a n b e d e v e l o p e d f o r s p e c i a l c a s e s. S o m e s o l u t i o n s a r e a v a i l a b l e f o r d e t e r m i n a t i o n o f a p p r o x i m a t e o r l i m i t i n g c a s e s. If t h e c o m p r e s s i b l e l a y e r t h i c k n e s s H is l a r g e r e l a t i v e t o t h e w i d t h o f t h e l o a d e d a r e a B, t h e n t h e r e w i l l be a n i m m e d i a t e s e t t l e m e n t s. in E q u a t i o n (9). Its m a g n i t u d e c a n b e e s t i m a t e d u s i n g e l a s t i c t h e o r y. T h e c o n s o l i d a t i o n s e t t l e m e n t, s c o n s in t h e s e c a s e s m a y b e r e d u c e d d e p e n d i n g o n _ t h e m a g n i t u d e of t h e p o r e p r e s s u r e c o e f f i c i e n t A. E s t i m a t i o n of c o n s o l i d a t i o n s e t t l e m e n t s a c c o r d i n g t o t h e p r o c e d u r e o f S k e m p t o n a n d B j e r r u m (1957) m a y be a p p r o p r i a t e. L a t e r a l d r a i n a g e b e c o m e s i m p o r t a n t in a c c e l e r a t i n g the r a t e o f c o n s o l i d a t i o n w h e n t h e v a l u e of H / B e x c e e d s t o 1.0, d e p e n d i n g o n t h e s h a p e of l o a d e d a r e a a n d w h e t h e r t h e c o m p r e s s i b l e l a y e r is s i n g l y o r d o u b l y d r a i n e d. T h e r a t e o f s e t t l e m e n t w i l l be e v e n g r e a t e r if t h e h o r i z o n t a l p e r m e a b i l i t y, a n d t h e r e f o r e c v _jj, is g r e a t e r t h a n t h e v e r t i c a l p e r m e a b i l i t y a n d cv _ y. A q u a n t i t a t i v e e s t i m a t e o f b o t h o f t h e s e e f f e c t s c a n be m a d e u s i n g t h e s o l u t i o n s d e v e l o p e d by D a v i s a n d P o u l o s (1972). W h e n v e r t i c a l d r a i n s a r e u s e d, t h e c o e f f i c i e n t o f v e r t i c a l c o n s o l i d a t i o n d u e to h o r i z o n t a l flow, c v _jj, c o n t r o l s t h e r a t e of c o n s o l i d a t i o n. B o t h s p e c i a l l a b o r a t o r y t e s t s o n l a r g e s a m p l e s, e.g., H a n s b o (1960), R o w e (1964), B e r r y a n d W i l k i n s o n (1969), a n d P a u t e (1973), a n d i n - s i t u t ests, s u m m a r i z e d b y M i t c h e l l a n d G a r d n e r (1975), h a v e b e e n u s e d to d e t e r m i n e c.. A m a j o r d i f - v h f i c u l t y in l a b o r a t o r y t e s t i n g for d e t e r m i n a t i o n o f c v _^ is t h a t v e r y l a r g e s a m p l e s a r e r e q u i r e d in m a n y c a s e s if r e s u l t s r e p r e s e n t a t i v e of the t r u e i n - s i t u s t r a t i f i c a t i o n a r e to be o b t a i n e d. A n a p p r o a c h t h a t h a s y i e l d e d r e a s o n a b l e r e s u l t s is to m e a s u r e k ^ in t h e f i e l d a n d c o m p u t e c v _^ u s i n g a c o m p r e s s i b i l i t y v a l u e d e t e r m i n e d b y c o n v e n t i o n a l l a b o r a t o r y t e s t s. A t y p i c a l c o n d i t i o n is t h a t c, / c = 2 to 10. v - h v - v P r e c o m p r e s s i o n b y E l e c t r o - o s m o s i s B e c a u s e w a t e r c a n b e m a d e to f l o w t h r o u g h f i n e g r a i n e d s o i l s f r o m a n o d e to c a t h o d e in a d i r e c t c u r r e n t e l e c t r i c a l field; i.e., b y e l e c t r o o s m o s i s, c o n s o l i d a t i o n w i l l r e s u l t if w a t e r is r e m o v e d at t h e c a t h o d e b u t n o t r e p l a c e d at the a n o d e. F o r c e r t a i n s o i l c o n d i t i o n s a n d l i m i t e d s o i l v o l u m e s, e l e c t r o - o s m o s i s m a y b e an e c o n o m i c a l a n d e f f e c t i v e m e a n s f o r c o n s o l i d a t i o n. If, a t t h e s a m e t i m e as w a t e r is b e i n g r e m o v e d at t h e c a t h o d e, s t a b i l i z i n g c h e m i c a l s a r e i n j e c t e d a t t h e anode, s o i l i m p r o v e m e n t b y e l e c t r o - k i n e t i c i n j e c t i o n c a n b e a c h i e v e d. E l e c t r o - k i n e t i c i n j e c t i o n is d i s c u s s e d in a l a t e r section. T h e m e c h a n i s m of e l e c t r o - o s m o s i s h a s b e e n e l a b o r a t e d by G r a y a n d M i t c h e l l (1967). T h e t h e o r y for c o n s o l i d a t i o n b y e l e c t r o - o s m o s i s h a s b e e n d e v e l o p e d b y E s r i g (1968), W a n a n d M i t c h e l l (1976), a n d M i t c h e l l a n d W a n (1977). R e c e n t case h i s t o r i e s a r e s u m m a r i z e d b y P i l o t (1977). T h e w a t e r f l o w rate, in a o n e - d i m e n s i o n a l d i r e c t c u r r e n t f i e l d is i n i t i a l l y 3, = k i A h e e ( m / s e c ) (18) 525

18 w h e r e k g = 1 x to 7 x m / s e c p e r v o l t / m where k^ = the hydraulic conductivity i = e l e c t r i c a l p o t e n t i a l g r a d i e n t (volt/m) Yw = t h e u n i t w e i g h t o f w a t e r A = c r o s s - s e c t i o n a l a r e a ( m 2 ) A l t e r n a t i v e l y, t h e f l o w r a t e c a n b e e x p r e s s e d by q ^ = k^ I ( m 3/sec) (19) w h e r e k. = w a t e r f l o w p e r u n i t t i m e p e r a m p e r e 1 ( m 3/ s e c / a m p ) I = c u r r e n t (amps) T h e c o e f f i c i e n t s k e a n d k^ a r e r e l a t e d b y the s p e c i f i c e l e c t r i c a l c o n d u c t i v i t y, a, V = v o l t a g e (a f u n c t i o n o f p o s i t i o n ) T h e a m o u n t of c o n s o l i d a t i o n a s s o c i a t e d w i t h t h i s e f f e c t i v e s t r e s s i n c r e a s e is o b t a i n e d f r o m a v o i d r a t i o vs. e f f e c t i v e p r e s s u r e r e l a t i o n s h i p for t h e s o i l d e t e r m i n e d in t h e u s u a l m a n n e r. S t r e n g t h i n c r e a s e s, in t h e a b s e n c e o f e l e c t r o c h e m i c a l h a r d e n i n g e f f e c t s, c a n b e e s t i m a t e d in t h e s a m e way. T h e r a t e o f c o n s o l i d a t i o n is g o v e r n e d b y the s a m e r e l a t i o n s h i p s t h a t a p p l y to c o n s o l i d a t i o n u n d e r d i r e c t l y a p p l i e d l o a d i n g. T h e t i m e t for a g i v e n d e g r e e o f c o n s o l i d a t i o n is k. = k /a (20) l e V a l u e s o f o r a n g e f r o m a b o u t 0.02 m h o / m f o r l o w s a l t c o n t e n t s o i l s to m h o / m f o r h i g h s a l t c o n t e n t s o i l s. V a l u e s o f k^ f o r w a t e r c o n t e n t s in the r a n g e o f 50 t o 100 p e r c e n t a r e g i v e n in T a b l e III. T h e p o w e r c o n s u m p t i o n P is g i v e n b y P = q h A V / k i x l 0-3 (kwh) (21) w h e r e A V is t h e v o l t a g e drop. S o i l T y p e T A B L E III V a l u e s of E l e c t r o - O s m o t i c W a t e r T r a n s p o r t C o e f f i c i e n t (Water c o n t e n t r a n g e %) P o r e W a t e r S a l t C o n c e n t r a t i o n (N) 3 k i m / s e c / a m p w h e r e T L = t i m e f a c t o r f o r t h e s p e c i f i e d d e g r e e o f c o n s o l i d a t i o n a n d b o u n d a r y c o n d i t i o n s = e l e c t r o d e s p a c i n g c = c o e f f i c i e n t o f c o n s o l i d a t i o n, v V a l u e s o f T f o r d i f f e r e n t d e g r e e s of c o n s o l i d a t i o n for t h e c a s e o f p a r a l l e l p l a t e e l e c t r o d e s w i t h a l i n e a r v a r i a t i o n in v o l t a g e b e t w e e n t h e m a r e g i v e n in T a b l e IV. M e a s u r e m e n t s b y J o h n s t o n a n d B u t t e r f i e l d (1977) i n d i c a t e t h a t r a t h e r t h a n a l i n e a r v a r i a t i o n in v o l t a g e b e t w e e n e l e c t r o d e s, a n i n s t a n t a n e o u s l y i n f i n i t e e l e c t r i c a l g r a d i e n t d e v e l o p s a t t h e a n o d e i n i t i a l l y w h i c h d e c r e a s e s in a c o n s i s t e n t way, to a u n i f o r m g r a d i e n t at t h e c o m p l e t i o n o f c o n s o l i d a t i o n. V a l u e s o f T for t h e s e c o n d i t i o n s a r e a l s o l i s t e d in T a b l e IV. It m a y b e s e e n t h a t c o n s o l i d a t i o n o c c u r s m o r e r a p i d l y f o r t h e l a t t e r case. S i l t y clay, k a o l i n i t e S i l t y clay, k a o l i n i t e I x l 0 - s - 5 x l 0 " 7 N 1 o x l l x l 0-7 T A B L E IV T i m e F a c t o r f o r V a r i o u s D e g r e e s o f C o n s o l i d a t i o n b y E l e c t r o - o s m o s i s B e t w e e n P a r a l l e l P l a t e E l e c t r o d e s C l a y (illitic) C l a y (illitic) x i 0 " 8-6 x l 0 " B 1 o x l x l 0-8 D e g r e e of C o n s o l i d a t i o n D <%) L i n e a r V V a r i a t i o n T i m e Factor, T I n f i n i t e I n i t i a l G r a d i e n t D u r i n g c o n s o l i d a t i o n, t h e w a t e r f l o w r a t e d e c r e a s e s w i t h t ime. It c e a s e s w h e n a h y d r a u l i c g r a d i e n t, c a u s e d b y a d e c r e a s e in p o r e w a t e r p r e s s u r e a t t h e a n o d e r e l a t i v e t o t h a t at t h e c a t h o d e, c a u s i n g f l o w f r o m c a t h o d e t o w a r d s a n o d e, e x a c t l y b a l a n c e s t h e e l e c t r i c a l l y i n d u c e d h y d r a u l i c g r a d i e n t c a u s i n g f l o w f r o m a n o d e t o w a r d s cathode. A t t h i s c o n d i t i o n t h e i n c r e a s e in e f f e c t i v e s t r e s s, A a ', f r o m t h a t at the s t a r t o f t r e a t m e n t is Aa- = (ke / k h ) yw V (22)

19 A c t u a l e l e c t r o d e a r r a n g e m e n t s a r e a n a r r a y o f r o d s o r p i p e s, s p a c e d t y p i c a l l y a t 2 t o 4 m e t e r s in p a t t e r n s, r a t h e r t h a n p a r a l l e l flat p l a t e s. In a d d i t i o n, v a r i a t i o n s in p r o p e r t i e s, e s p e c i a l l y in t h e r a t i o k g / k ^, t h a t d e v e l o p d u r i n g c o n s o l i d a t i o n l e a d to d e v i a t i o n s f r o m t h e t h e o r y ( M i t c h e l l a n d Wan, ). T h u s the v a l u e s in T a b l e IV c a n b e u s e d o n l y as an a p p r o x i m a t i o n for p r e d i c t i o n o f c o n s o l i d a t i o n time. A n a l y s i s o f t h e e l e c t r i c a l f l o w s f o r d i f f e r e n t e l e c t r o d e a r r a n g e m e n t s, Fig. 22, s h o w s t h a t a h e x a g o n a l a r r a n g e m e n t is e f f i c i e n t in t e r m s o f (1) p o w e r c o n s u m p t i o n, (2) a v e r a g e v o l t a g e (the h i g h e r t h e a v e r a g e v o l t a g e t h e g r e a t e r t h e a v e r a g e a m o u n t o f c o n s o l i d a t i o n t h a t c a n b e o b t a i n e d f o r a g i v e n a p p l i e d v o l t a g e ), a n d (3) a n o d e t o c a t h o d e r a t i o. O o 0 o o 0 / o y o 0 o 0 o 0 O r*i 0 * » o o O o o o o o o o o-*^ 0O r *1 o + o o ^ o o t * o o < o > o o o o o o o + o SQoort Pattern StrotgM SQuOft Potttrn Stoççe red HtMogonot Potttrn 0 O Cathode o o Anode o A, > o i * V o Arto/Basic Unit 5* 2 S S 2 Anodts/Boslc Uni! / / 2 Cothodts/Umt Arto 0.5/S2 0.5/S* 038/ S 2 Anodts/Uni! Arto 0.5/S2 0.5/ /S2 A v»rag» Volto gè, V 0.5V 0.5 V 074 V Power/Uni! Arto (for some V) Power/Uni! Arto (for somt P; Fig V ^ S V2/fiS V2/ p S 2 /ovfys* 2 40 P2//>S2 / /OP2/e>S2 V * Applitd Voilage p Rtsistivity C h a r a c t e r i s t i c s o f D i f f e r e n t E l e c t r o d e P a t t e r n s in E l e c t r o - o s m o s i s I n c r e a s i n g t h e n u m b e r o f a n o d e s r e l a t i v e to c a t h o d e s is g e n e r a l l y b e n e f i c i a l f o r t w o r e a s o n s. W e l l p o i n t s a r e o f t e n u s e d f o r c a t h o d e s, w h e r e as, r e i n f o r c i n g b a r s o r a l u m i n u m r o d s a r e u s e d as a n o d e s. H e n c e, a n o d e s c o s t l ess. I r o n a n d a l u m i n u m a n o d e s d e c o m p o s e d u r i n g t r e a t m e n t a n d p a r t i c i p a t e i n e l e c t r o - c h e m i c a l h a r d e n i n g r e a c t i o n s t h a t g i v e s t r e n g t h i n c r e a s e s b e y o n d t h o s e a t t r i b u t a b l e s o l e l y to c o n s o l i d a t i o n. In a p p l i c a t i o n it is k n o w n t h a t e l e c t r o - o s m o s i s m a y b e e f f e c t i v e a n d e c o n o m i c a l u n d e r the f o l l o w i n g c o n d i t i o n s : 1. S a t u r a t e d s i l t s o r s i l t y c l a y s o i l s 2. N o r m a l l y c o n s o l i d a t e d c o n d i t i o n s 3. L o w p o r e w a t e r e l e c t r o l y t e c o n c e n t r a t i o n. Gas g e n e r a t i o n a n d d r y i n g a n d f i s s u r i n g a t the e l e c t r o d e s c a n i m p a i r t h e e f f i c i e n c y o f the m e t h o d a n d l i m i t t h e m a g n i t u d e o f c o n s o l i d a t i o n p r e s s u r e s t h a t d e v e l o p. T r e a t m e n t r e s u l t s in n o n - u n i f o r m c h a n g e s in p r o p e r t i e s b e t w e e n e l e c t r o d e s, b e c a u s e t h e i n d u c e d c o n s o l i d a t i o n d e p e n d s o n t h e v o l t a g e, a n d t h e v o l t a g e v a r i e s b e t w e e n a n o d e a n d c a t h o d e. T h u s r e v e r s a l of e l e c t r o d e p o l a r i t y m a y b e d e s i r a b l e to a c h i e v e a m o r e u n i f o r m s t r e s s c o n d i t i o n. E l e c t r o o s m o s i s m a y a l s o b e u s e d to a c c e l e r a t e the O o o c o n s o l i d a t i o n u n d e r a p r e l o a d o r s u r c h a r g e fill. A n a l y s i s m e t h o d s f o r t h e s e c o n d i t i o n s a r e p r e s e n t e d by W a n a n d M i t c h e l l (1976). R e c e n t D e v e l o p m e n t s S e v e r a l r e c e n t s t u d i e s h a v e b e e n d i r e c t e d a t the d e v e l o p m e n t o f n e w a p p r o a c h e s to a n d a p p l i c a t i o n s f o r p r e c o m p r e s s i o n. S o m e s t u d i e s h a v e b e e n m a d e (Leong, 1977) of c o n s o l i d a t i o n i n d u c e d by i n f l a t a b l e c y l i n d r i c a l m e m b r a n e s in v e r t i c a l b o r e h o l e s. O n e c a n imagine, for e x a m p l e, a h e x a g o n a l p a t t e r n of e x p a n d a b l e m e m b r a n e s in l i e u o f t h e a n o d e s in Fig. 22 w h i c h i n d u c e an e x c e s s p r e s s u r e in t h e s u r r o u n d i n g s o i l and, h e n c e, w a t e r f l o w t o w a r d s d r a i n w e l l s at p o s i t i o n s s h o w n b y c a t h o d e s in t h e f i g u r e. T h e m a g n i t u d e of c o n s o l i d a t i o n t h a t c a n b e p r o d u c e d is d e p e n d e n t o n the e x c e s s p o r e p r e s s u r e t h a t c a n b e i n d u c e d, w h i c h, in t urn, d e p e n d s o n t h e i n f l a t a b l e m e m b r a n e d i a m e t e r, h o l e s p a c i n g a n d c o n f i g u r a t i o n, s o i l s t r e n g t h, a n d soil s t r e s s - s t r a i n p r o p e r t i e s. R e c e n t s t u d i e s of c o n s o l i d a t i o n u s i n g b o t h v e r t i c a l a n d r a d i a l c y c l i c l o a d s h a v e b e e n s u m m a r i z e d b y S c h l o s s e r a n d J u r a n (1979). D e n s e l y p a c k e d q u i c k l i m e p i l e s in s oft, s a t u r a t e d c l a y h a v e b e e n u s e d. F o u r e f f e c t s a r e b e n e f i c i a l : 1. W a t e r is t a k e n f r o m t h e s o i l t o h y d r a t e t h e l i m e. 2. H y d r a t i o n o f q u i c k l i m e is a c c o m p a n i e d b y a s p e c i f i c g r a v i t y d e c r e a s e f r o m 3.3 to 2.2. T h i s l e a d s to e x p a n s i o n a g a i n s t t h e b o r e h o l e a n d d e v e l o p m e n t o f p o r e p r e s s u r e in t h e n a t i v e s oil. R e c e n t e x p e r i m e n t s b y K u r o d a e t al. (1980) s h o w e d t h a t e x p a n s i o n p r e s s u r e s i n e x c e s s o f 2 M P a c o u l d be d e v e l o p e d f o r c o n d i t i o n s of l o w p o r o s i t y a n d r e s t r a i n e d e x p a n s i o n. 3. T h e h e a t o f h y d r a t i o n h e l p s to f u r t h e r reduce t h e w a t e r c o n t e n t. 4. S l o w d i f f u s i o n o f l i m e i n t o t h e s u r r o u n d i n g s o i l l e a d s t o c e m e n t a t i o n a n d g r o u n d s t r e n g t h e n i n g. T h e n e e d for d e n s i f i c a t i o n of f i n e - g r a i n e d s l u r r i e s, s l u d g e s, a n d s l i m e s h a s b e c o m e a m a j o r c o n c e r n in t h e c o n t a i n m e n t a n d s t o r a g e o f d i s p o s a l m a t e r i a l s a n d t h e s u b s e q u e n t u t i l i z a t i o n o f d i s p o s a l s i t e s. D e w a t e r i n g a n d d e n s i f i c a t i o n of t h e s e m a t e r i a l s b y s p e c i a l d r a i n a g e a n d c o n s o l i d a t i o n s y s t e m s c a n b e a m o n g t h e m o s t e f f e c t i v e t e c h n i q u e s a v a i l a b l e ( J o h n s o n e t al., 1977). S e e p a g e c o n s o l i d a t i o n ; i.e., s u r f a c e p o n d i n g w i t h o u t s u r f a c e m e m b r a n e s b u t w i t h u n d e r d r a i n age, c a n be e s p e c i a l l y u s e f u l b e c a u s e o f t h e g r e a t e r e f f e c t i v e s t r e s s e s t h a t c a n be d e v e l o p e d. P r e f a b r i c a t e d d r a i n s c a n b e u t i l i z e d e f f e c t i v e l y b o t h w i t h i n a n d b e n e a t h t h e m a t e r i a l s to b e d e n s i f i e d. B e c a u s e o f t h e l a r g e v o l u m e c h a n g e s a n d s t r a i n s i n v o l v e d, n e w c o n s o l i d a t i o n t h e o r i e s h a v e b e e n d e v e l o p e d f o r a n a l y s i s of t h e s e m a t e r i a l s. T h e w o r k o f Imai (1978) a n d S o m o g y i et al. (1981) is u s e f u l in t h i s r e g a r d. F i n a l l y, p r e c o m p r e s s i o n w i t h v e r t i c a l d r a i n s is n o w b e i n g u s e d in c o n j u n c t i o n w i t h o t h e r m e t h o d s o f g r o u n d i m p r o v e m e n t a n d r e i n f o r c e m e n t. T w o r e c e n t e x a m p l e s m a y b e c i t e d. A t t h e C h a n g i A i r p o r t in S i n g a p o r e a l o o s e s a n d f i l l w a s p l a c e d o v e r a t h i c k l a y e r o f s o f t clay. 527

20 P r e f a b r i c a t e d d r a i n s w e r e i n s t a l l e d to a d e p t h o f 43 m to a c c e l e r a t e c o n s o l i d a t i o n of t h e c lay. H e a v y t a m p i n g w a s t h e n u s e d t o d e n s i f y t h e s a n d f i l l (Hansbo, 1978). A t t h e s i t e of t h e e a s t a p p r o a c h e m b a n k m e n t to t h e D u m b a r t o n B r i d g e c u r r e n t l y u n d e r c o n s t r u c t i o n a c r o s s t h e s o u t h e r n e n d o f 'the S a n F r a n c i s c o Bay, t h e s o f t m u d f o u n d a t i o n s o i l h a s a s h e a r s t r e n g t h l e s s t h a n 5 k P a. C o n s o l i d a t i o n u n d e r t h e p r o p o s e d e m b a n k m e n t w o u l d h a v e t a k e n 30 to 40 y e a r s. S p e c i a l m e a s u r e s w e r e t h e r e f o r e r e q u i r e d to p r o v i d e e m b a n k m e n t s u p p o r t a n d t o a c c e l e r a t e t h e a n t i c i p a t e d s e t t l e m e n t o f 2 m. T h e s o l u t i o n, s h o w n in Fig. 23, c o n s i s t e d o f (1) a g e o t e x t i l e r e i n f o r c e m e n t to d i s t r i b u t e e m b a n k m e n t l o a d i n g a n d r e d u c e d i f f e r e n t i a l s e t t l e m e n t, (2) l i g h t w e i g h t f i l l (sawdust) to r e d u c e l o a d i n g, (3) p r e f a b r i c a t e d v e r t i c a l d r a i n s to r e d u c e t h e c o n s o l i d a t i o n t i m e to less t h a n o n e y e a r, a n d (4) a g e o t e x t i l e f i l t e r to p r e v e n t c o n t a m i n a t i o n of a d r a i n a g e b l a n k e t. I N J E C T I O N A N D G R O U T I N G I n t r o d u c t i o n In F r e n c h e n g i n e e r C h a r l e s B e r i g u y r e p a i r e d a s c o u r i n g s l u i c e at D i e p p e b y i n j e c t i n g a g r o u t o f c l a y a n d h y d r a u l i c l i m e b e n e a t h it. S i n c e t h e n i n j e c t i o n o f m a t e r i a l s i n t o t h e g r o u n d has d e v e l o p e d i n t o a w i d e l y u s e d m e t h o d f o r s o i l s t a b i l i z a t i o n a n d g r o u n d i m p r o v e m e n t. B e c a u s e of its h i g h c ost, g r o u t i n g is u s u a l l y l i m i t e d to z o n e s o f r e l a t i v e l y s m a l l v o l u m e a n d to s p e c i a l p r o b l e m s t h a t c a n n o t b e s o l v e d b y o t h e r m e t h o d s. M o s t o f t h e e a r l y a p p l i c a t i o n s o f g r o u t i n g w e r e f o r g r o u n d w a t e r c o n t r o l o r s h u t off, a n d t h e s e c o n t i n u e t o b e v e r y i m p o r t a n t a p p l i c a t i o n s today. M o r e r e c e n t l y i n j e c t i o n s h a v e b e e n u s e d for g r o u n d s t r e n g t h e n i n g a n d g r o u n d m o v e m e n t control, a n d it is t h e s e a p p l i c a t i o n s t h a t a r e of p r i m a r y c o n c e r n i n t h i s r e p o r t. T h r e e m o d e s of i n j e c t i o n a r e p o s s i b l e, as s h o w n in Fig. 24: Elisting Alignment 'fee: E rn b o n k m e n t S t r u t s Mom Embonkment o s R e q u ire d P erro M o r io 1 : ^ te. s r p il»er F o b n c *----- ^ Sowilust Fill m Critical Ai ^ R e in fo rc in g F o b ric B o y M u d j _ L - V e r t ic o l W ic k D ra m s F i g. 23 G e n e r a l i z e d C r o s s S e c t i o n S h o w i n g S t a b i l i z a t i o n M e a s u r e s a t t h e S i t e o f t h e D u m b a r t o n B r i d g e A p p r o a c h F i l l ( Hannon, 1980) a) Permeation b) Displacement c) Encapsulation S a n d - 7* 1 Permeated sand Grout fills voids Compaction grout Grout bulb displaces surrounding soil Grout fluid surrounds intact chunks of soil Fig. 24 Types of Grouting 528

21 1. P e r m e a t i o n g r o u t i n g i n w h i c h t h e g r o u t f i l l s s o i l p o r e s. T h e r e is e s s e n t i a l l y no c h a n g e in t h e v o l u m e o r s t r u c t u r e o f t h e o r i g i n a l g r o u n d. T h i s t y p e o f g r o u t i n g c a n g e n e r a l l y o n l y be a c c o m p l i s h e d in s o i l s c o a r s e r t h a n f i n e s a n d s a n d in f i s s u r e d rocks. 2. D i s p l a c e m e n t ^ g r O u t i n g in w h i c h a s t i f f m i x t u r e f i l l s v o i d s a n d c o m p r e s s e s t h e s u r r o u n d i n g soil. 3. E n c a p s u l a t i o n in w h i c h n a t u r a l l y f r a g m e n t e d g r o u n d o r g r o u n d f r a c t u r e d h y d r a u l i c a l l y u n d e r h i g h g r o u t f l u i d p r e s s u r e s is i n j e c t e d b y g r o u t w h i c h c o a t s b u t d o e s n o t p e r m e a t e t h e i n d i v i d u a l c h u n k s o f soil. A le n s s t r u c t u r e in t h e f o r m o f a c a r d h o u s e is f o rmed. R e c e n t r e f e r e n c e s t h a t p r e s e n t c o m p r e h e n s i v e r e v i e w s o f i n j e c t i o n a n d g r o u t i n g i n c l u d e A S C E (1980), B o w e n (1975), C a m b e f o r t (1973), C a r o n et al. (1975), H e r n d o n a n d L e n a h a n (1976), K i r s c h a n d S a m o l (1978), a n d L e n z i n i a n d B r u s s (1975). A l t h o u g h s u c c e s s f u l g r o u t i n g m a y be c o m p l i c a t e d, it is m o r e t h a n a n art. S o m e u n d e r l y i n g c o n c e p t s h a v e b e e n d e f i n e d, a n d p r i n c i p l e s g u i d i n g its s u c c e s s h a v e b e e n e s t a b l i s h e d. It is t h e s e t h a t a r e t h e f o c u s o f t h i s s e c t i o n. A p p l i c a t i o n s A n u m b e r o f a p p l i c a t i o n s o f g r o u t i n g f o r s o i l i m p r o v e m e n t a p a r t f r o m s e e p a g e c o n t r o l m a y be n o t e d, i n c l u d i n g : 1. V o i d f i l l i n g to p r e v e n t e x c e s s i v e s e t t l e m e n t. 2. G r o u n d s t r e n g t h e n i n g u n d e r e x i s t i n g s t r u c t u r e s to p r e v e n t m o v e m e n t s d u r i n g a d j a c e n t e x c a v a t i o n, p i l e d r i v i n g, etc. 3. G r o u n d m o v e m e n t c o n t r o l d u r i n g t u n n e l i n g o p e r a t i o n s. T a n a n d C l o u g h (1980) p r e s e n t a d e s i g n m e t h o d f o r d e t e r m i n i n g t h e r e q u i r e d s i z e a n d s t r e n g t h of s t a b i l i z e d z o n e s a r o u n d t u n n e l s f o r e f f e c t i v e g r o u n d m o v e m e n t c o n t r o l. 4. S o i l s t r e n g t h e n i n g to r e d u c e l a t e r a l s u p p o r t r e q u i r e m e n t s. 5. S o i l s t r e n g t h e n i n g t o i n c r e a s e t h e l a t e r a l l o a d r e s i s t a n c e of piles. 6. S t a b i l i z a t i o n o f l o o s e s a n d s a g a i n s t l i q u e f a c t i o n. 7. F o u n d a t i o n u n d e r p i n n i n g. 8. S l o p e s t a b i l i z a t i o n. 9. V o l u m e c h a n g e c o n t r o l o f e x p a n s i v e s o i l s t h r o u g h p r e s s u r e i n j e c t i o n o f l i m e s l u r r y. T h i s t e c h n i q u e is c o n t r o v e r s i a l a n d l i k e l y to b e e f f e c t i v e o n l y u n d e r s p e c i a l c o n d i t i o n s ( I ngles a n d N e i l, 1970; W r i g h t, 1973; B l a c k l o c k, 1975; T h o m p s o n a n d R o b n e t t, 1976). G r o u t T y p e s P e r m e a t i o n g r o u t s a r e of t w o types. P a r t i c u l a t e g r o u t s a r e m a d e u p o f c e m e n t, soil, o r c l a y a n d m i x t u r e s o f these. C h e m i c a l g r o u t s a r e c o m p o s e d o f v a r i o u s m a t e r i a l s in s o l u t i o n. D i s p l a c e m e n t o r c o m p a c t i o n g r o u t s a r e s t i f f, l o w s l u m p (0 to 50 mm) m i x t u r e s o f c e m e n t, soil, a n d / o r c l a y a n d w a t e r. L i m e s l u r r i e s a r e t h e m o s t c o m m o n l y u s e d e n c a p s u l a t i o n - t y p e g r o u t s ; h o w e v e r, t h e r e is no i n h e r e n t r e a s o n, e x c e p t p e r h a p s for e c o n o m i c s. why other chemicals could not be used. P a r t i c u l a t e G r o u t s N e a t c e m e n t a n d s o i l - c e m e n t g r o u t s a r e t h e m o s t c o m m o n l y u s e d p a r t i c u l a t e g r o u t s, a l t h o u g h s o i l - w a t e r g r o u t s h a v e b e e n u s e d in s o m e c a s e s. In w a t e r - c e m e n t g r o u t s w a t e r : c e m e n t r a t i o s of 0.5:1 to 6 : 1 h a v e b e e n u s e d. W i t h l o w w a t e r : c e m e n t r a t i o s t h e r e is l e s s s e g r e g a t i o n a n d f i l t e r i n g, a n d h i g h e r s t r e n g t h s a r e o b t a i n e d, b u t t h e y are h a r d e r t o i n j e c t t h a n g r o u t s w i t h a h i g h e r w a t e r c o n t e n t. C h e m i c a l a d d i t i v e s a r e s o m e t i m e s u s e d to f a c i l i t a t e p e n e t r a t i o n, to p r e v e n t c e m e n t f l o c c u l a t i o n, a n d to c o n t r o l s e t times. Set t i m e s c a n b e as s h o r t as 30 s e c o n d s o r v e r y long. In s o i l - c e m e n t g r o u t s a s o i l v o l u m e o f f o u r to s i x t i m e s t h e l o o s e v o l u m e o f c e m e n t is common. W a t e r v o l u m e s f r o m o n e t h i r d to t w i c e t h e s o i l v o l u m e p e r b a g o f c e m e n t a r e u s e d. T h e l o w w a t e r c o n t e n t m i x e s a r e t y p i c a l of h i g h v i s c o s i t y d i s p l a c e m e n t g r o u t s. Z e r o s l u m p c o m p a c t i o n g r o u t s w i t h 30 t o 60 s e c o n d g e l t i m e s c a n be m a d e u s i n g c e m e n t, clay, a n d f l y a s h m i x e s w i t h a n a l k a l i n e a c c e l e r a t o r. If b e n t o n i t e is u s e d, e x p a n d e d p a r t i c l e s m a y c o l l a p s e if t h e g r o u n d w a t e r h a s a h i g h s a l t c o n t e n t. C a r e s h o u l d be t a k e n in the u s e o f c e m e n t in t h e p r e s e n c e o f s u l f a t e - b e a r i n g s o i l s o r g r o u n d w a t e r. P a r t i c u l a t e g r o u t s c a n n o t be i n j e c t e d as p e r m e a t i o n g r o u t s i n t o s o i l s f i n e r t h a n m e d i u m to c o a r s e s a n d s. S o m e " g r o u t a b i l i t y r a t i o s " t h a t h a v e p r o v e n u s e f u l a r e Fo r soils: N = ^P 15^ s o i l ^ 85^ g r o u t N > 24 : g r o u t i n g c o n s i s t e n t l y p o s s i b l e N < 11 : g r o u t i n g n o t p o s s i b l e N < c F o r rock: li ^ D 1 0 soil N C = T D T g r o u t g r o u t i n g c o n s i s t e n t l y p o s s i b l e g r o u t i n g n o t p o s s i b l e W i d t h o f f i s s u r e (D9 5 )g r o u t N > 5 : g r o u t i n g c o n s i s t e n t l y p o s s i b l e K N R < 2 : g r o u t i n g n o t p o s s i b l e A d d i t i o n a l g u i d e l i n e s r e l a t i n g to p a r t i c u l a t e g r o u t t y p e s a n d p a r t i c l e s i z e are: T y p e s I a n d II P o r t l a n d c e m e n t a r e s u i t a b l e for s o i l s c o a r s e r t h a n mm. T y p e III P o r t l a n d c e m e n t is s u i t a b l e for s o i l s c o a r s e r t h a n 0.42 mm. B e n t o n i t e is s u i t a b l e f o r s o i l s c o a r s e r t h a n mm. C h e m i c a l G r o u t s C h e m i c a l g r o u t s o f f e r the a d v a n t a g e s o v e r p a r t i c u l a t e g r o u t s t h a t t h e y c a n p e n e t r a t e s m a l l e r 35. Volyme 4 529

22 p o r e s, as m a y b e s e e n in Fig. 25, t h e y h a v e a l o w e r v i s c o s i t y, a n d t h e r e is a b e t t e r c o n t r o l o f s e t t ime. O n t h e o t h e r h a n d t h e i r t e c h n o l o g y is m o r e c o m p l e x a n d c o s t s a r e h i g h. S o i l s c o n t a i n i n g l e s s t h a n 10 p e r c e n t f i n e s (<74 y m p a r t i cles) c a n u s u a l l y b e p e r m e a t i o n g r o u t e d w i t h c h e m i c a l s. If the f i n e s c o n t e n t is g r e a t e r t h a n 15 p e r c e n t e f f e c t i v e c h e m i c a l g r o u t i n g m a y be d i f f i c u l t. F o r f i n e s c o n t e n t g r e a t e r t h a n 20 p e r c e n t p e r m e a t i o n g r o u t i n g w i l l n o t b e p o s s i b l e, b u t c h e m i c a l g r o u t s c a n b e d i s t r i b u t e d a l o n g a n d t h r o u g h h y d r a u l i c f r a c t u r e s. T h e m o s t c o m m o n c h e m i c a l g r o u t c l a s s e s a r e s i l i c a t e s, l i g n i n s, r e s i n s, a c r y l a m i d e s, and u r e t h a n e s. H u n d r e d s o f d i f f e r e n t f o r m u l a t i o n s h a v e b e e n d e v e l o p e d w i t h i n t h e s e c l a s s e s. Of them, h o w e v e r, t h e s i l i c a t e s a c c o u n t for m o r e t h a n 90 p e r c e n t o f p r e s e n t c h e m i c a l g r o u t use, t h e o t h e r s b e i n g l i m i t e d for r e a s o n s o f c o s t and t o x i c i t y. " T w o - s h o t " s i l i c a t e s y s t e m s, in w h i c h a f i r s t i n j e c t i o n o f s o d i u m s i l i c a t e is f o l l o w e d b y a s e c o n d i n j e c t i o n o f a m a t e r i a l s u c h a s C a C l 2 to c a u s e f o r m a t i o n o f i n s o l u b l e p r e c i p i t a t e d s i l i c a gel, h a v e l a r g e l y g i v e n w a y to o n e - s h o t s i l i c a t e s y s t e m s. P r e m i x e d c o m b i n a t i o n s o f s o d i u m s i l i c a t e a n d a p p r o p r i a t e c a t a l y s t s a n d a c t i v a t o r s a r e f o r m u l a t e d t o g i v e s p e c i f i e d d e s i g n s t r e n g t h a n d s e t t i n g times. A t w o - s h o t s i l i c a t e C O 2 g a s s y s t e m h a s b e e n d e v e l o p e d a n d is u s e d in the l o e s s s o i l s of t h e U S S R ( S o k o l o v i c h, 1973). A m m o n i a g a s i n j e c t i o n h a s a l s o b e e n f o u n d e f f e c t i v e in l o e s s w h e r e i n o n l y m o d e s t s t r e n g t h e n i n g is r e q u i r e d to p r e v e n t c o l l a p s e. T h e r e a c t i o n is to r e p l a c e a d s o r b e d C a + + b y N H ^ +. T h e l i b e r a t e d C a + + c o m b i n e s w i t h w a t e r to f o r m C a f O H ^, w h i c h a c t s as a c e m e n t i n g s t a b i l i z e r. G r o u t s c o n t a i n i n g 25 t o 30 p e r c e n t s i l i c a t e a r e t y p i c a l for w a t e r p r o o f i n g a p p l i c a t i o n s. W h e r e h i g h s t r e n g t h is r e q u i r e d for s t r u c t u r a l a p p l i c a t i o n s, s i l i c a t e c o n c e n t r a t i o n s of 40 to 60 p e r c e n t a r e u s e d. U n i q u e l o c a l c h e m i c a l c o n d i t i o n s m a y i n f l u e n c e r e a c t i v i t y. T e m p e r a t u r e e f f e c t s, d i l u t i o n b y g r o u n d w a t e r, c a t a l y s t a d s o r p t i o n b y sand, a n d o t h e r f a c t o r s m a y i n f l u e n c e g e l t i m e a n d c h a r a c t e r o f t h e r e s u l t a n t g r o u t. A c c o r d i n g l y, p r e l i m i n a r y t e s t i n g is d e s i r a b l e. T h e p r o p e r t i e s o f c h e m i c a l l y g r o u t e d s a n d s c o v e r a w i d e r a n g e. S o m e t y p i c a l v a l u e s o f v i s c o s i t y a n d c o m p r e s s i v e s t r e n g t h f o r d i f f e r e n t g r o u t Grove/ Sortd sat Clay I I I I 1 (Concentration, %) Portland Cement Viscosity, cps (water=!) ICompressive Strength, kn/m2] Silicates (IO) I 5, (30) 15 [< > Resins (10)1.4, (30)3.5, (40)9, (5 0 )3 0 [>3000] Lignins (10)1.4, (30) II, [< ] Acrylamides (10)1.3, (30)1.7, (50)2.5 [ ] 1 0 t.o 0.1 O.OI O.OOl Soil Particle Size -mm Fig. 25 S o i l P a r t i c l e S i z e s f o r D i f f e r e n t G r o u t T y p e s a n d G r o u t e d S o i l P r o p e r t i e s 530

23 t y p e s a n d t h e p a r t i c l e s i z e r a n g e for w h i c h t h e y a r e s u i t e d a r e s h o w n in Fig. 25. T h e u n c o n f i n e d c o m p r e s s i v e s t r e n g t h o f c h e m i c a l l y g r o u t e d s a n d m a y r a n g e f r o m 0. 3 t o m o r e t h a n 10 MPa. T h e r e s u l t s of t r i a x i a l t e s t s, e.g., P e r e z et al. (1981), i n d i c a t e t h a t g r o u t i n g p r o d u c e s an i n c r e a s e in the c o h e s i o n i n t e r c e p t b u t h a s l i t t l e e f f e c t o n the f r i c t i o n a n g l e. T h e s t i f f n e s s o f s i l i c a t e g r o u t e d s a n d i n c r e a s e s w i t h c o n f i n i n g p r e s s u r e in a b o u t t h e s a m e w a y as a n u n g r o u t e d sand. S t r e s s - s t r a i n b e h a v i o r is n o n - l i n e a r. S t r e n g t h a n d s t i f f n e s s d e c r e a s e as l o a d i n g r a t e d e c r e a s e s, c r e e p o c c u r s u n d e r c o n s t a n t load, a n d c r e e p r u p t u r e m a y d e v e l o p u n d e r h i g h s t r e s s l e v e l s. T h e s e a s p e c t s of b e h a v i o r a r e i m p o r t a n t w h e n g r o u t i n g is u s e d in u n d e r p i n n i n g, t u n n e l i n g, a n d o p e n c u t c o n s t r u c t i o n. T h e r e s u l t s of r e c e n t s t u d i e s o n t h e s e a s p e c t s of g r o u t e d s o i l p r o p e r t i e s a r e g i v e n b y C l o u g h e t al. (1979), G a r t u n g a n d K a n y (1975), a n d P e r e z e t al. (1981). S y n e r e s i s, i.e., a t i m e - d e p e n d e n t t i g h t e n i n g of t h e g e l s t r u c t u r e r e s u l t i n g i n f i s s u r i n g, m a y o c c u r in s i l i c a t e - g r o u t e d sands, a n d t h e s e r i o u s n e s s o f t h e r e s u l t i n g p r o b l e m s i n c r e a s e s w i t h i n c r e a s i n g s i l i c a t e c o n c e n t r a t i o n. In c a s e s w h e r e s e a l i n g t h e s e c r a c k s, as w e l l as o t h e r s t h a t m a y h a v e f o r m e d b y h y d r a u l i c f r a c t u r i n g d u r i n g t h e i n j e c t i o n p r o c e s s, is r e q u i r e d, a s e c o n d i n j e c t i o n s t a g e u s i n g a c e m e n t g r o u t * tu b e s a m an chettes * m a y b e n e e d e d. E q u i p m e n t a n d T e c h n i q u e s T h e d e s i g n o f a s u c c e s s f u l g r o u t i n g p r o g r a m r e q u i r e s n o t o n l y t h e s e l e c t i o n o f a s u i t a b l e g r o u t m a t e r i a l, b u t a l s o t h e c o r r e c t d r i l l i n g e q u i p m e n t, p r o c e d u r e s, a n d g r o u t h o l e p a t t e r n s. It is e s s e n t i a l t h a t t h e p i p e s a n d i n j e c t i o n p o r t s b e in t h e r i g h t p l a c e. It is m o r e i m p o r t a n t to e n s u r e t h a t t h e f u l l d e s i g n s o i l v o l u m e is p e r m e a t e d w i t h g r o u t w h e n t h e o b j e c t i v e is w a t e r c u t o f f t h a n w h e n t h e o b j e c t i v e is to i m p r o v e m e c h a n i c a l p r o p e r t i e s. B o t h b a t c h a n d c o n t i n u o u s f l o w s y s t e m s c a n be u s e d e f f e c t i v e l y. B a t c h s y s t e m s g i v e b e t t e r m i x i n g of c o m p o n e n t s, b u t r e q u i r e l o n g e r g e l t i m e s t h a n do c o n t i n u o u s f l o w s y s t e m s. Gel t i m e s o f 50 to 90 min. a r e c o m m o n for b a t c h s y s t e m s. C o n t i n u o u s f l o w s y s t e m s m a y g i v e b e t t e r p l a c e m e n t c o n t r o l b u t a r e m o r e c o m p l e x. H o l e s p a c i n g s of a b o u t 1. 3 m to 2.5 m a r e t y p i cal. C o s t s b e c o m e e x c e s s i v e f o r s m a l l e r s p a c ings, a n d g r o u t p l a c e m e n t in d e s i r e d l o c a t i o n s c a n ' t be e n s u r e d if l a r g e r s p a c i n g s a r e used. B o t h o p e n - p i p e a n d s l e e v e - p i p e (tube a manchettes) i n j e c t i o n m e t h o d s a r e used, as s h o w n i n Fig. 26. A l t h o u g h t h e s l e e v e - p i p e m e t h o d is m o r e e x p e n sive, it is b e c o m i n g w i d e l y u s e d b e c a u s e it g i v e s m u c h b e t t e r c o n t r o l o f g r o u t l o c a t i o n. T h e r e c e n t t e s t p r o g r a m a t L o c k s a n d D a m No. 26 d e s c r i b e d b y P e r e z e t al. (1981) is a n e x c e l l e n t c o m p a r a t i v e s t u d y o f t h e t w o m e t h o d s. A t t h i s s i t e m u l t i p l e - s t a g e s l e e v e - p i p e g r o u t i n g w a s m u c h m o r e e f f e c t i v e t h a n o p e n - b o t t o m p i p e g r o u t i n g. T h e u s e of g e l t i m e s l e s s t h a n t h e p u m p i n g time, t e r m e d f a s t g e l times, h a s t h e a d v a n t a g e s o f g r o u t l o c a t i o n c o n t r o l in f l o w i n g g r o u n d w a t e r a n d in s t r a t i f i e d s o i l s. It a l s o w i l l l i m i t Fig. 26 I n j e c t i o n M e t h o d s (Caron e t al., 1975) g r o u t t a k e s in v e r y p e r v i o u s m a t e r i a l s. P u m p i n g t i m e to g e l t i m e r a t i o s o f 10 a r e c o m m o n. T h e d i s a d v a n t a g e of f a s t g e l t i m e s, o f c o u r s e, is t h a t h u m a n or m e c h a n i c a l f a i l u r e c a n l e a d to g r o u t s e t u p in t h e e q u i p m e n t. A c o m m o n r u l e o f t h u m b f o r m a x i m u m i n j e c t i o n p r e s s u r e f o r o p e n p i p e g r o u t i n g is a b o u t 20 kpa/m; i.e., a v a l u e e q u a l to t h e o v e r - b u r d e n p r e s s u r e, u n l e s s g r o u t i n g u n d e r a h e a v y s t r u c t u r e o r i n a s i t u a t i o n w i t h g r e a t e r c o n f i n e m e n t. V a l u e s two to t h r e e t i m e s as g r e a t m a y b e u s e d w i t h f a s t gel t i m e s y s t e m s. B e c a u s e o f t h e n e e d to o p e n t h e r u b b e r s l e e v e a n d to b r e a k t h r o u g h t h e p l a s t i c g r o u t s h e a t h w i t h the t u b e a m a c h e t t e m e t h o d, h i g h p r e s s u r e s m a y b e r e q u i r e d i n i t i a l l y. H i g h i n i t i a l p r e s s u r e s m a y a l s o b e u s e f u l if it is d e s i r e d to o p e n u p t h e f o r m a t i o n b y h y d r a u l i c f r a c t u r i n g. E l e c t r o c h e m i c a l I n j e c t i o n J u s t as d i r e c t e l e c t r i c a l c u r r e n t c a n be u s e d in l i e u o f a p h y s i c a l l o a d i n g to c o n s o l i d a t e a c o m p r e s s i b l e soil, it c a n be u s e d a l s o to m o v e s o l u t i o n s i n t o a n d t h r o u g h a p o r o u s m a t e r i a l in l i e u o f a h y d r a u l i c i n j e c t i o n p r e s s u r e. B e c a u s e t h e c o e f f i c i e n t of e l e c t r o - o s m o t i c p e r m e a b i l i t y, k e, is i n s e n s i t i v e t o p a r t i c l e s i z e a n d g e n e r a l ly f a l l s w i t h i n a n a r r o w r a n g e o f a b o u t 1 x t o 7 x c m / s e c / v o l t / c m, a u n i t e l e c t r i c a l g r a d i e n t (1 v o l t / c m ) c a n b e m o r e e f f e c t i v e t h a n a u n i t h y d r a u l i c g r a d i e n t for m o v i n g f l u i d s t h r o u g h f i n e r g r a i n e d soils. H e n c e, e l e c t r o - k i n e t i c i n j e c t i o n m i g h t be c o n s i d e r e d f o r u s e in 531

24 s i l t y s o i l s w h i c h c a n n o t b e i n j e c t e d u s i n g o r d i n a r y g r o u t i n g t e c h n i q u e s. E l e c t r o - k i n e t i c i n j e c t i o n m i g h t be u s e f u l a l s o w h e r e l a c k o f c o n f i n e m e n t p r e v e n t s g r o u t i n g in t h e u s u a l way. C h e m i c a l s t a b i l i z e r s a r e i n t r o d u c e d a t t h e a n o d e a n d c a r r i e d t o w a r d t h e c a t h o d e u s i n g e l e c t r i c a l g r a d i e n t s of t h e o r d e r o f 50 to 100 v o l t s p e r m e t e r. S e v e r a l e x p e r i e n c e s w i t h e l e c t r o c h e m i c a l i n j e c t i o n up to t h e m i d ' s a r e s u m m a r i z e d by P i l o t (1977). O ' B a n n o n e t al. (1976) d e s c r i b e t h e e l e c t r o c h e m i c a l h a r d e n i n g o f e x p a n s i v e clay. O n c e s c u a n d B a l l y (1977) u s e d an e l e c t r o - k i n e t i c i n j e c t i o n o f s o d i u m s i l i c a t e to s t r e n g t h e n t h e l o e s s u n d e r t h e f o u n d a t i o n s o f a t h e a t e r. " P i l e s " o f t r e a t e d s o i l 3 to 4 m l o n g a n d 1.6 to 2.2 m in d i a m e t e r w e r e f o r m e d. B a k e r, ). G r o u t b u l b s w e r e i n s e r t e d via 76 m m d i a m e t e r p i p e s p l a c e d 3 m a p a r t to p r o v i d e s u p p o r t b e t w e e n t h e t u n n e l c r o w n, a f t e r the s h i e l d p a s s e d, a n d t h e g r o u n d s u r f a c e. T h e s c h e m e is s h o w n s c h e m a t i c a l l y in Fig. 27. P u m p ing p r e s s u r e s a v e r a g e d a b o u t 2 MPa, i n j e c t i o n d e p t h s w e r e a b o u t 12 m b e l o w g r o u n d s u r f a c e, and w o r k w a s c a r r i e d o u t a b o u t 2 m b e h i n d t h e shield. T h e e l e c t r o - k i n e t i c s t a b i l i z a t i o n o f a p o t e n t i a l l y l i q u e f i a b l e s a n d h a s b e e n i n v e s t i g a t e d b y Y a m a n o u c h i a n d M a t s u d a (1975). T h e c o n c e p t w a s to fill t h e v o i d s of t h e l o o s e s a n d w i t h a g e l o r c o l l o i d a l m a t e r i a l a n d t h u s p r e v e n t c o l l a p s e u n d e r c y c l i c l o a d i n g s. S i l i c a t e s o l u t i o n s, b e n t o n i t e, a n d a l u m i n u m h y d r o x i d e w e r e i n v e s t i g a t e d as i n j e c t i o n m a t e r i a l s. T h e b e n t o n i t e a n d a l u m i n u m h y d r o x i d e, as n e g a t i v e l y c h a r g e d c o l l o i d s, w e r e i n j e c t e d a t t h e c a t h o d e a n d m o v e d i n t o t h e p o r e s b y e l e c t r o - p h o r e s i s. T h e r e s u l t s d e m o n s t r a t e d a m a r k e d i n c r e a s e in r e s i s t a n c e to l i q u e f a c t i o n a f t e r t r e a t m e n t. S e g a l l et al. (1980) r e p o r t t h e r e s u l t s o f a l a r g e n u m b e r o f c h e m i c a l a n a l y s e s on w a t e r l e a c h e d b o t h h y d r a u l i c a l l y a n d b y e l e c t r o o s m o s i s f r o m d r e d g e d soil. It w a s f o u n d t h a t b e c a u s e o f the e l e c t r o c h e m i c a l r e a c t i o n s at e l e c t r o d e s, t h e e l e c t r o - o s m o s i s w a t e r b e c a m e v e r y a l k a l i n e (ph = 13.4). A s a r e s u l t o r g a n i c m a t e r i a l s w e n t i n t o s o l u t i o n. H e a v y m e t a l s w e r e d e s o r b e d a n d c a r r i e d o u t at t h e c a t h o d e, as w e r e a l s o p e s t i c i d e s. D e p o s i t s of i r o n o x i d e, m a g n e s i u m h y d r o x i d e, a n d c a l c i u m c a r b o n a t e w e r e f o r m e d in t h e s o i l n e a r t h e anode. T h e s e r e s u l t s s u g g e s t a p o t e n t i a l l y u s e f u l a p p r o a c h to c l e a n i n g u p h a z a r d o u s w a s t e - c o n t a m i n a t e d soil. D i s p l a c e m e n t ( C o m p a c t i o n ) G r o u t i n g H i g h l y v i s c o u s soil, c e m e n t, a n d w a t e r d i s p l a c e m e n t or c o m p a c t i o n g r o u t a c t s as a r a d i a l h y d r a u l i c j a c k w h i c h c o m p r e s s e s t h e s u r r o u n d i n g soil. T h e h a r d e n e d g r o u t m i x t u r e is a b u l b of strong, r e l a t i v e l y i n c o m p r e s s i b l e m a t e r i a l. D i s p l a c e m e n t g r o u t i n g c a n b e u s e d in p a r t l y s a t u r a t e d s o i l m a s s e s a n d l o o s e m a t e r i a l s c o n t a i n i n g v o i d s p a c e s. I t is u s e d to c o r r e c t d i f f e r e n t i a l s e t t l e m e n t s o r t o p r o v i d e u n d e r p i n n i n g a n d g r o u n d s t r e n g t h e n i n g a d j a c e n t to o p e n e x c a v a t i o n or t u n n e l i n g a c t i v i t i e s. A v a i l a b l e e q u i p m e n t c a n d e v e l o p u p t o 2.5 to 3.0 M N / m 2 p u m p i n g p r e s s u r e, a n d z e r o s l u m p g r o u t c a n b e p u m p e d d i s t a n c e s in e x c e s s of 30 m. T o be e f f e c t i v e, c o m p a c t i o n g r o u t i n g s h o u l d n o t be u n d e r t a k e n at d e p t h s less t h a n 1 to 2 m u n l e s s t h e r e is an o v e r l y i n g s t r u c t u r e to p r o v i d e c o n f i n e m e n t. C o m p a c t i o n g r o u t i n g m a t e r i a l s a n d p r o c e d u r e s a r e d e s c r i b e d b y W a r n e r a n d B r o w n (1974), G r a f (1969), a n d W a r n e r (1978), a m o n g o t h e r s. R e c e n t ly, d u r i n g c o n s t r u c t i o n o f t h e B a l t i m o r e, M a r y land, U. S. A. s u b w a y n e a r t h e B o l t o n H i l l Station, the p r o j e c t e d c o s t o f u n d e r p i n n i n g e x i s t i n g s t r u c t u r e s w a s so h i g h t h a t c o m p a c t i o n g r o u t i n g w a s u s e d to p r e v e n t s u r f a c e s u b s i d e n c e ( H a y w a r d Fig. 27 J e t G r o u t i n g C o m p a c t i o n G r o u t i n g D u r i n g T u n n e l i n g t o P r e v e n t S e t t l e m e n t s A n e w g r o u t i n g t e c h n i q u e t e r m e d j e t g r o u t i n g w a s i n t r o d u c e d in J a p a n s e v e r a l y e a r s a g o (Yahiro a n d Y o s h i d a, 1973; M i k i, 1973; M i k i et al., 1980). T h e b a s i s f o r j e t g r o u t i n g is a s p e c i a l h i g h s p e e d w a t e r j e t a c t i n g u n d e r a n o z z l e p r e s s u r e o f 15 to 70 MPa. T h e n a t i v e s o i l m a y b e m i x e d in p l a c e w i t h a s u i t a b l e s t a b i l i z e r as s h o w n in Fig. 28. A l t e r n a t i v e l y, p o o r s o i l s c a n be r e m o v e d b y i n - s i t u e x c a v a t i o n a n d r e p l a c e d b y a m o r t a r g r o u t t o f o r m hard, i m p e r v i o u s c o l u m n s, p a n e l s o r s h e e t s, as s h o w n s c h e m a t i c a l l y in Fig. 29. J e t g r o u t e d c o l u m n s u p to 3 m in d i a m e t e r a r e p o s s i b l e. T h e u s e of a i r j e t t i n g in c o n j u n c t i o n w i t h g r o u t j e t t i n g c a n y i e l d d i a m e t e r s u p to t w i c e as g r e a t, for a g i v e n jet p r e s s u r e, as t h e g r o u t j e t alone. T h e m e t h o d o f f e r s t h e a d v a n t a g e s o f b o t h c l o s e c o n t r o l o v e r t h e z o n e s b e i n g t r e a t e d a n d a p p l i c a b i l i t y to c l a y s as w e l l as sands. M i k i e t al. (1980) r e p o r t an i n c r e a s e in u n c o n f i n e d c o m p r e s s i v e s t r e n g t h o f an o r i g i n a l l y s o f t c l a y e y soil to 1.5 to 4 M P a, s o m e 30 t i m e s t h e o r i g i n a l s t r e n g t h. T h e s e c a n t m o d u l u s at 50 p e r c e n t of t h e f a i l u r e s t r e s s w a s i n c r e a s e d b y a f a c t o r of 200. E v a l u a t i o n of E f f e c t i v e n e s s P r e c i s e d e t e r m i n a t i o n of e x a c t l y w h e r e a l l the g r o u t w e n t in t h e g r o u n d is u s u a l l y n o t possible. A s s e s s m e n t o f g r o u t i n g e f f e c t i v e n e s s is u s u a l l y m a d e o n t h e b a s i s o f g r o u t t a k e r e c o r d s a n d t h e r e s u l t s of i n - s i t u t e s t s a n d l a b o r a t o r y t e s t s on 532

25 I. Beginning of drilling 2. End of drilling Revolving Beginning and of lateral drawing up jetting of jetting Completion rod TABLE V M a x i m u m P r o p e r t y V a l u e s f o r S i l i c a t e G r o u t e d S a n d (Data f r o m P e r e z e t al., 1981; s e e t e x t f o r d e t a i l s ) U ltra high pressure pulse pump D rilling m achine Fig. 28 M i x e d - i n - P l a c e C o l u m n s M a d e by J e t G r o u t i n g r e c o v e r e d s a m p l e s. A m o n g t h e t e s t s t h a t h a v e b e e n u s e d to e v a l u a t e g r o u t i n g d o n e f o r g r o u n d s t r e n g t h e n i n g p u r p o s e s a r e t h e c o n e p e n e t r a t i o n test, t h e s t a n d a r d p e n e t r a t i o n test, t h e p r e s - s u r e m e t e r t est, p l a t e l o a d t e s t s, a n d c o m p r e s s i o n a n d s h e a r w a v e v e l o c i t y tests. A c o u s t i c e m i s s i o n m o n i t o r i n g d u r i n g g r o u t i n g h a s b e e n u s e d r e c e n t l y as a m e a n s f o r d e t e c t i o n o f h y d r a u l i c f r a c t u r i n g a n d l o c a t i o n o f g r o u t flow. F r o m t h e t e s t p r o g r a m at L o c k s a n d D a m No. 26 r e p o r t e d by P e r e z e t al. (1981), t h e m a x i m u m l e v e l s of p r o p e r t y i m p r o v e m e n t o b t a i n e d u s i n g t h e m o s t e f f e c t i v e g r o u t i n g p r o c e d u r e ( m u l t i p l e s t a g e s l e e v e pipe) a n d a h i g h s t r e n g t h s i l i c a t e g r o u t a r e l i s t e d in T a b l e 5. T h e u n g r o u t e d s a n d w a s f i n e - t o - m e d i u m r - g r a i n e d w i t h l e s s t h a n 5 p e r c e n t fines. It w a s m e d i u m d e n s e a n d c o h e s i o n l e s s w i t h a c o e f f i c i e n t of p e r m e a b i l i t y o f 5 x l 0-3 to 3 x 1 0 ' 2 c m / s e c. T h e s e l e v e l s of i m p r o v e m e n t a r e p r o b a b l y the m a x i m u m t h a t c a n be e x p e c t e d u s i n g c u r r e n t m a t e r i a l s a n d t e c h n o l o g y. P r o p e r t y S P T - N v a l u e ( b l o w s / 0. 3 m) U n g r o u t e d S a n d G r o u t e d S a n d C P T - q c ( k g / c m 2 ) S h e a r w a v e v e l o c i t y (m/sec) C o e f f. of E a r t h P r e s s u r e at R est, K q Une. C o m p. S t r e n g t h (kpa) 1500 C o h e s i o n (kpa) F r i c t i o n a n g l e ( ) P l a t e L o a d T e s t M o d u l u s (MPa) P r e s s u r e m e t e r M o d u l u s (MPa) U l t i m a t e S t r e s s, P l a t e L o a d T e s t (kpa) P r e s s u r e m e t e r L i m i t P r e s s u r e (MPa) C o e f f i c i e n t of P e r m e a b i l i t y (cm/sec) A D M I X T U R E S T A B I L I Z A T I O N I n t r o d u c t i o n > x x O f t h e m a n y m e t h o d s o f g r o u n d i m p r o v e m e n t, the u s e of a d m i x t u r e s o f v a r i o u s t y p e s is t h e o l d e s t a n d m o s t w i d e s p r e a d. C h e m i c a l a d m i x t u r e s, m o s t c o m m o n l y l i m e a n d c e m e n t, h a v e b e e n u s e d to i m p r o v e t h e p r o p e r t i e s of soils, b y i o n e x c h a n g e Execution plant (1) Guide Hole Excavation Drill 3-inch hole to bottom of treatment area and place concentric mortar tremie and jet pipes in hole. Fig. 29 (2) Monitor Setting A monitor is lowered to the predetermined depth and Jetting direction is set. (3) Jetting and Grouting Simultaneously rotate and lift the jet nozzle at the specified speeds. The soil is eroded by the jet and removed from the borehole in the resulting flushing foam. Cut-off Wall Construction by Jet Grouting (4) Execution of next panel. Steps (2) and (3) are repeated. 533

26 a n d c e m e n t a t i o n r e a c t i o n s, f o r u s e in p a v e m e n t s t r u c t u r e s for c e n t u r i e s. T h e r e is a v a s t b o d y o f l i t e r a t u r e c o n c e r n e d w i t h c l a s s i c a l " s o i l s t a b i l i z a t i o n ; " i.e., t h e i m p r o v e m e n t of s u b g r a d e a n d b a s e c o u r s e m a t e r i a l s. B e c a u s e of the r e a d y a v a i l a b i l i t y of t h i s i n f o r m a t i o n, it w i l l n o t be s u m m a r i z e d in t h i s r e v i e w. A m o n g the c o m p r e h e n s i v e r e c e n t r e f e r e n c e s a r e I n g l e s a n d M e t c a l f (1973), Y a m a n o u c h i (1975), W i n t e r k o r n (1975), T r a n s p o r t a t i o n R e s e a r c h B o a r d (1975, 1976, 1977), M i t c h e l l (1976), T e r r e l e t a l. (1979). D u r i n g t h e ' s s o i l - c e m e n t b e c a m e w i d e l y u s e d in h y d r a u l i c s t r u c t u r e s, e s p e c i a l l y f o r t h e u p s t r e a m s l o p e p r o t e c t i o n o f e a r t h d a m s ( N u s s b a u m a n d C o l l e y, 1971; H o l t z a n d H a n s e n, 1976). S o i l - c e m e n t h a s b e e n u s e d for p o n d l i n i n g s a n d d i k e s, a n d s t u d i e s h a v e b e e n m a d e c o n c e r n i n g t h e c o n s t r u c t i o n o f c o m p l e t e d a m s o f s o i l - c e m e n t (Raphael, 1976, R o b e r t s o n a n d B l i g h t, 1978). A d v a n c e s in t h e ' s in s o i l i m p r o v e m e n t u s i n g a d m i x t u r e s h a v e i n c l u d e d b o t h t h e d e v e l o p m e n t of n e w m a t e r i a l s a n d e x t e n d e d a p p l i c a t i o n s of c o n v e n t i o n a l m a t e r i a l s, m o s t n o t a b l y the u t i l i z a t i o n of l i m e a n d c e m e n t in s t r u c t u r a l f i l l s a n d w i t h d e e p m i x i n g m e t h o d s. Principles of Admixture Stabilization T h e g e n e r a l o b j e c t i v e s of m i x i n g c h e m i c a l a d d i t i v e s w i t h s o i l a r e t o i m p r o v e o r c o n t r o l v o l u m e s t a b i l i t y, s t r e n g t h a n d s t r e s s - s t r a i n p r o p e r t i e s, p e r m e a b i l i t y, a n d d u r a b i l i t y. V o l u m e s t a b i l i t y ( c o n t r o l o f s w e l l i n g a n d s h r i n k a g e ) c a n b e i m p r o v e d b y r e p l a c e m e n t o f h i g h h y d r a t i o n c a t i o n s s u c h as s o d i u m b y l o w h y d r a t i o n c a t i o n s s u c h as c a l c i u m, m a g n e s i u m, a l u m i n u m, o r iron; b y c e m e n t a t i o n ; a n d b y w a t e r p r o o f i n g c h e m i c a l s. T h e d e v e l o p m e n t a n d m a i n t e n a n c e of h i g h s t r e n g t h a n d s t i f f n e s s is a c h i e v e d b y e l i m i n a t i o n of l a r g e p o r e s, b y b o n d i n g p a r t i c l e s a n d a g g r e g a t e s t o g e t h e r, b y m a i n t e n a n c e o f f l o c c u l e n t p a r t i c l e a r r a n g e m e n t s, a n d b y p r e v e n t i o n of s w e l l i n g. T h e p e r m e a b i l i t y is a l t e r e d b y m o d i f i c a t i o n of p o r e s i z e a n d p o r e s i z e d i s t r i b u t i o n. T h e a c t i o n s of o r g a n i c a n d i n o r g a n i c s t a b i l i z e r s a r e g e n e r a l l y q u i t e d i f f e r e n t. T h e o r g a n i c s a r e c h a r a c t e r i z e d b y a r a p i d s t r e n g t h gain, t h e n c o n s t a n t p r o p e r t i e s w i t h t i m e. O f t h e m a n y o r g a n i c m a t e r i a l s t h a t h a v e b e e n p r o p o s e d for u s e as a d m i x t u r e s ; e. g., a c r y l a m i d e s, r e s i n s, p o l y u r e t h a n e s, p o l y e s t e r s, o n l y a s p h a l t h a s h a d c o n s i s t e n t u s e in l a r g e q u a n t i t i e s. E x c e p t for s p e c i a l a p p l i c a t i o n s s u c h as g r o u t i n g, c o s t h a s l i m i t e d t h e u s e o f t h e o t h e r s. T h e s t a b i l i z a t i o n m e c h a n i s m s o f l i m e a n d P o r t l a n d c e m e n t, t h e t w o m o s t c o m m o n l y u s e d i n o r g a n i c a d m i x t u r e s t a b i l i z e r s, a r e s i m i l a r. E n d p r o d u c t s a r e a s e r i e s of c a l c i u m s i l i c a t e h y d r a t e s ( C S H ). L i m e a c q u i r e s s i l i c a f r o m c l a y s o r o t h e r p o z z o l a n s in t h e s o i l to f o r m C S H gel. C e m e n t c o n t a i n s s i l i c a i n i t i a l l y. S h o r t t e r m r e a c t i o n s w i t h c e m e n t a n d l i m e i n c l u d e r e p l a c e m e n t o f m o n o v a l e n t a d s o r b e d c a t i o n s b y Ca++, a d s o r p t i o n o f C a ( 0H >2 b y p a r t i c l e s, c e m e n t a t i o n a t i n t e r p a r t i c l e c o n t a c t s, a n d e s t a b l i s h m e n t of a h i g h p H (12.4) e n v i r o n m e n t. In t h e l o n g t e r m t h e p H c a u s e s a b r e a k d o w n o f t h e c r y s t a l l a t t i c e o f c l a y a n d f o r m a t i o n of c e m e n t i t i o u s p r o d u c t s. T h e s e r e a c t i o n s c a n c o n t i n u e for y e a r s. L i m e a n d c e m e n t a r e e f f e c t i v e in a w i d e r a n g e of s o i l t y p e s. S o m e o r g a n i c c o m p o u n d s, h o w e v e r, c a n r e t a r d o r i n h i b i t r e a c t i o n s. In a d d i t i o n, it is u s e f u l to k e e p in m i n d t h a t t h e p r e s e n c e o f free s u l f a t e s in c l a y s o i l s c a n b e d e t r i m e n t a l. A s f i r s t d e m o n s t r a t e d b y S h e r w o o d (1962) a n d r e i t e r a t e d b y I n g l e s a n d M e t c a l f (1973), i n i t i a l s t a b i l i z a t i o n m a y b e s a t i s f a c t o r y, b u t s u b s e q u e n t w e t t i n g c a n l e a d to e x p a n s i o n a n d b r e a k d o w n of t h e c e m e n t e d s t r u c t u r e. Attainment of good mixing of stabilizers with soil is the most important factor affecting the quality of results. Both subdivision of the soil and distribution of the additive are important. Much of the success of the new deep mixing methods discussed later must be attributed to the development of equipment capable of mixing admixtures with soft, heavy clays to a reasonable degree of uniformity. Properties of Lime-and Cement-Treated Soils T h e s p e c i f i c v a l u e s of a n y p r o p e r t y o f an a d m i x t u r e - s t a b i l i z e d s o i l c a n fall w i t h i n a w i d e r a n g e d e p e n d i n g o n s o i l type, s t a b i l i z e r t y p e a n d a m o u n t, c u r i n g c o n d i t i o n s, a n d o t h e r f a c t o r s. T h e u n c o n f i n e d c o m p r e s s i v e s t r e n g t h is a n e a s i l y - m e a s u r e d p r o p e r t y t h a t c a n o f t e n be u s e d as a b a s i s f o r e s t i m a t e s of o t h e r p r o p e r t i e s. L i m e t r e a t m e n t l e v e l s o f 3 p e r c e n t t o 8 p e r c e n t b y w e i g h t o f d r y s o i l a r e t y p i c a l f o r i m p r o v e m e n t o f p l a s t i c a n d e x p a n s i v e f i n e - g r a i n e d soils. A p p r o x i m a t e v a l u e s f o r m e c h a n i c a l p r o p e r t i e s o f w e l l - m i x e d l i m e - t r e a t e d s o i l a r e g i v e n in T a b l e VI. P o r t l a n d c e m e n t a t t r e a t m e n t l e v e l s o f 3 t o 10 p e r c e n t b y d r y w e i g h t is p a r t i c u l a r l y w e l l - s u i t e d f o r l o w p l a s t i c i t y s o i l s a n d s a n d y soils. R a n g e s o f p r o p e r t i e s f o r g r a n u l a r a n d f i n e g r a i n e d c e m e n t - t r e a t e d s o i l s a r e l i s t e d in T a b l e VII. T h e v a l u e s in T a b l e s VI a n d V I I a r e for w e l l - m i x e d t r e a t m e n t s a n d c o m p a c t i o n at w a t e r c o n t e n t s n e a r o p t i m u m. T h e y m a y be r e p r e s e n t a t i v e f o r a d m i x t u r e - s t a b i l i z e d s o i l s u s e d as s t r u c t u r a l fills. T h e y w i l l b e s u b s t a n t i a l l y in e x c e s s of w h a t c a n b e e x p e c t e d f o r i n - p l a c e t r e a t m e n t s b y d e e p m i x i n g, b e c a u s e (1 ) t h e w a t e r c o n t e n t s in t h i s c a s e w i l l b e m u c h h i g h e r a n d (2) t h e m i x i n g w i l l n o t be as g ood. N e w S t a b i l i z e r M a t e r i a l s A m o n g t h e r e c e n t l y d e v e l o p e d a d m i x t u r e s f o r s o i l i m p r o v e m e n t t w o d e s e r v e p a r t i c u l a r c o m m e n t b e c a u s e o f t h e i r u n i q u e n e s s a n d p o t e n t i a l. I n g l e s a n d L i m (198 0) d e s c r i b e a n e w a p p r o a c h to c l a y s t a b i l i z a t i o n i n v o l v i n g t h e u s e o f i r o n o x i d e. T h e p r o c e s s i n v o l v e s h e a t i n g a f i n e g r a i n e d s o i l to a t e m p e r a t u r e h i g h e n o u g h to d e s t r o y its w a t e r s e n s i t i v i t y, a d d i n g f i n e l y d i v i d e d i r o n o x i d e, a n d i n t r o d u c i n g a s o d i u m s i l i c a t e s o l u t i o n. A f t e r c o m p a c t i o n t h e m i x t u r e s e t s i n t o a h ard, d u r a b l e m a t e r i a l. R e s e a r c h i n J a p a n ( A r i i z u m i e t al.) h a s l e d t o d e v e l o p m e n t of a m a t e r i a l s u i t a b l e for s t r e n g t h e n i n g a n d d e t o x i f i c a t i o n of h i g h w a t e r c o n t e n t w a s t e s s u c h as d r e d g e d m a t e r i a l a n d sludge. A p r o d u c t t e r m e d c e m e n t b a c i l l u s (3CA0 A I 2O 3 3 C a S H 2O) is f o r m e d b y a d d i n g alumina, lime, a n d g y p s u m. T h e s e a d d i t i o n s m a y t h e m s e l v e s b e w a s t e s f r o m a v a r i e t y o f s o u r c e s. F o r e x a m p l e, t h e m a t e r i a l s u s e d in o n e c a s e w e r e 40 kg p a p e r slag, 30 kg s l a k e d lime, a n d 30 k g f l u e g a s d e s u l f u r i z a t i o n p e r 1 m 3 d r e d g e d " o o z e. " C o m p r e s s i v e s t r e n g t h s of t h e o r d e r o f 100 k P a d e v e l o p e d a f t e r 28 d ays. T h e f i x a t i o n of a l arge a m o u n t o f w a t e r as w a t e r o f c r y s t a l l i z a t i o n is 534

27 P r o p e r t i e s of C o m p a c t e d L i m e - S t a b i l i z e d S o i l q = U N C O N F I N E D C O M P R E S S I V E S T R E N G T H, k P a C O H E S I O N (c, kpa) : c = q u A N G L E O F I N T E R N A L F R I C T I O N (( >) : 25 < 4> < 35 C O M P R E S S I V E M O D U L U S (E, M P a A T 100 k P a C O N F I N I N G P R E S S U R E ) F L E X U R A L M O D U L U S TABLE VI E c = q u (Ef, MPa) E, = 4.6 f, f b M O D U L U S O F R U P T U R E (fb, k P a ) : f. = q b S P L I T T E N S I L E S T R E N G T H (ST, k P a ) : S T = q u P O I S S O N ' S R A T I O (y): U = 0.1 F O R L I M E M O D I F I E D S O I L S (qu < 70 k P a ) : C B R = (0.2 t o 0.25) q G E N E R A L I Z E D S T R E S S - S T R A I N C U R V E : Strain - % a n i m p o r t a n t f e a t u r e. L e a c h i n g t e s t s h a v e e s t a b l i s h e d t h a t h e a v y m e t a l s b e c o m e t i e d u p b y t h e c e m e n t b a c i l l u s, t h u s m a k i n g p o s s i b l e s a f e d i s p o s a l o f p o t e n t i a l l y t o x i c w a s t e s a s fill m a t e r i a l s. T h e r e s u l t s o f s i m i l a r s t u d i e s a r e r e p o r t e d b y K u r o d a et al. S t r u c t u r a l F i l l s V i r t u a l l y a n y i n o r g a n i c s o i l c a n b e p r o c e s s e d a n d t r e a t e d t o f o r m an a c c e p t a b l e s t r u c t u r a l f i l l m a t e r i a l. I n c r e a s i n g u s e is b e i n g m a d e of s u c h m a t e r i a l s f o r e m b a n k m e n t s a n d s u p p o r t of s t r u c t u r e s. S e v e r a l c a s e s a r e d e s c r i b e d b y t h e C o m m i t t e e o n P l a c e m e n t a n d I m p r o v e m e n t of S o i l s (1978). B l i g h t et al. (1977) d e s c r i b e t h e u s e o f c e m e n t e d t a i l i n g s f o r t h e b a c k f i l l i n g o f m i n e e x c a v a t i o n s. A t the C a n t o n, I l l i n o i s P o w e r P l a n t in t h e U.S.A. a l o e s s s o i l w a s s t a b i l i z e d u s i n g 3 p e r c e n t h y d r a t e d l i m e a n d 2-5 p e r c e n t f l y a s h to f o r m s t a b i l i z e d l a y e r s u p to 7.6 m in t h i c k n e s s. C o n v e n t i o n a l s t a b i l i z a t i o n e q u i p m e n t w a s u s e d, a n d c a r e f u l p u l v e r i z a t i o n, m i x i n g, a n d c o m p a c t i o n c o n t r o l s w e r e i m p l e m e n t e d. U n c o n f i n e d c o m p r e s s i v e s t r e n g t h s o f 1.0 to 1.4 M P a w e r e d e v e l o p e d a f t e r 4 d a y s c u r i n g a t 3 8 C. A s o i l - c e m e n t m a t 3.66 m t h i c k w a s u s e d to s u p p o r t a s t o r y o f f i c e b u i l d i n g in T a m p a, F l o r i d a in l i e u o f pile f o u n d a t i o n s, t h e m o r e u s u a l f o u n d a t i o n t y p e for t h a t a r e a. S a n d a n d c l a y w e r e e x c a v a t e d to e x p o s e a l a y e r o f c a v e r n o u s l i m e s t o n e w h i c h w a s f i l l e d w i t h l e a n c e m e n t a n d c o v e r e d b y t h e s o i l - c e m e n t. A r e m o v e a n d r e p l a c e o p t i o n w a s u s e d to e l i m i n a t e a l i q u e f a c t i o n d a n g e r in t h e s a n d s u n d e r l y i n g t h e K o e b e r g N u c l e a r P o w e r P l a n t in S o u t h A f r i c a. A n 8 m t h i c k l a y e r o f p o t e n t i a l l y l i q u e f i a b l e s a n d w a s r e m o v e d a n d t r e a t e d w i t h 5 p e r c e n t s u l f a t e r e s i s t a n t c e m e n t in a c e n t r a l m i x i n g p l a n t a n d r e c o m p a c t e d in l i f t s u s i n g c o n v e n t i o n a l e q u i p m e n t. T h e t o t a l v o l u m e of t r e a t e d m a t e r i a l w a s 2 0 0, m 3. A g r e a t d e a l of d y n a m i c t e s t i n g w a s u n d e r t a k e n in c o n n e c t i o n w i t h t h i s p r o j e c t, a n d a s u m m a r y o f t h e d y n a m i c p r o p e r t i e s of s a n d - c e m e n t h a s b e e n p r e s e n t e d b y D u p a s a n d P e c k e r (1979). S o i l - c e m e n t c u s h i o n s a r e w i d e l y u s e d in B u l g a r i a for t h e s u p p o r t o f s t r u c t u r e s o n c o l l a p s i b l e l o e s s d e p o s i t s. T h e l o e s s is t r e a t e d w i t h a b o u t 5 p e r c e n t c e m e n t a n d c o m p a c t e d in l a y e r s to f o r m m a t s u p t o s e v e r a l m e t e r s t h i c k. It h a s b e e n f o u n d t h a t t h e s e i s m i c s t a b i l i t y of s t r u c t u r e s f o u n d e d o n t h e s e c u s h i o n s is g r e a t l y i m p r o v e d ( M i n k o v e t al., 1980). L o e s s - c e m e n t c u s h i o n s h a v e b e e n u s e d a l s o in c o n j u n c t i o n w i t h h e a v y t a m p i n g. T h e s y s t e m a d o p t e d f o r a 180 m h i g h T V t o w e r f o u n d a t i o n e x e r t i n g a b e a r i n g p r e s s u r e of 230 k P a is s h o w n in Fig. 30. Deep Mixing Methods The in-situ mixing of admixtures, usually lime or Portland cement, with soft, fine-grained soils to form columns, piers, and walls has been studied and applied extensively in engineering practice in the last several years (Broms and Bowman, 1976, a, 1979b; S o k o l o v i c e t a l., 1976; O k u m u r a a n d T e r a s h i, 1975; P i l o t, 1977; T e r a s h i et al., 1979). A l t h o u g h d i f f e r e n t n a m e s are u s e d b y d i f f e r e n t o r g a n i z a t i o n s ; e.g., DCM, DCCM, Demic, P O C O M in J a p a n a n d l i m e c o l u m n s in S w e d e n, t h e c o n c e p t s, p r o c e d u r e s a n d a p p l i c a t i o n s are g e n e r a l l y s i m i l a r. C o l u m n s a r e p r o d u c e d b y f e e d i n g a m e t e r e d q u a n t i t y of s t a b i l i z e r i n t o a s o f t c l a y m a s s t h r o u g h a r o t a r y d r i l l e q u i p p e d w i t h a s p e c i a l a u g e r b i t to b o t h a d v a n c e to t h e d e s i r e d d e p t h a n d to m i x t h e s o i l a n d a d m i x t u r e t h o r o u g h l y d u r i n g w i t h d r a w a l. Fig. 31 is a s c h e m a t i c d i a g r a m of the p r o c e s s a s u s e d for c o n s t r u c t i o n o f a l i m e column. T h e m i x i n g b i t s u s e d in J a p a n a r e u s u a l l y s o m e w h a t l a r g e r a n d m o r e c o m p l e x, as s h o w n b y t h e p h o t o g r a p h i n Fig. 32, in c o m p a r i s o n t o t h e " e g g b e a t e r " m i x i n g t o o l u s e d in S w e d e n, Fig. 31. T h e a b i l i t y of t h e e q u i p m e n t t o d i s t r i b u t e the a d m i x t u r e t h o r o u g h l y f o r t h e full r e q u i r e d d e p t h a n d to m i x it u n i f o r m l y a c r o s s t h e c o l u m n is c r u c i a l to s u c c e s s. 535

28 TA B L E V I I Properties of Compacted Cement-Stabilized Soil PROPERTY GRANULAR SOILS FINE-GRAINED SOILS NOTES Density Unconfined Compressive Strength t/m t/irt UC = (500 to 1000) C K = 500 C (UC) UC = (300 to 600) C (UC) d + K log (x") o a K = 70 C May be higher or lower than untreated soil. Delay between mixing and compaction causes density and strength reductions. C = cement content,%?uc in kpa (UC)d = UC strength at age of ^ dq j jdays d = age (days) (d > dq ) Cohesion To a few thousand kpa To a few thousand kpa Depends on C, d c = (UC) kn/m2 Friction Angle Flexural and Tensile Strength Flexural Strength = (-g- to ^) compressive strength May decrease at high confining pressures Need 1-3% cement to develop CBR Modulus Compression CBR = (UC)1'45 7 x x 103 MPA 7 x 1 0 s - 7 x 106 Mpa E. = Kp l i (l-sin<t>) (O CT ) 2c cos(()+2ct^ sin1 in<p J i UC in kpa Depends on stress level E^ = initial tangent modulus Et = tangent modulus = confining pressure pa = atmospheric pressure n = K = ,000 Modulus-Tension and Flexure Same order of magnitude as in compression E E^ (usually) c t J Poisson*s Ratio Shrinkage A few tenths of one percent up to 1% Shrinkage cracks generally inevitable in thin slab construction. Permeability k < 1 x 10-6 cm/sec k < 1 x 10 6 cm/sec k parallel to compaction planes may be up to 20 times greater than normal to them. A l i m e c o l u m n d i a m e t e r o f 0.5 m is s t a n d a r d in S w e d e n for c o l u m n s u p to 10 m l o n g i n s t a l l e d u s i n g light, m o b i l e e q u i p m e n t. D i a m e t e r s up to m a n d d e p t h s to 60 m h a v e b e e n u s e d in J a p a n. In a d d i t i o n to l i m e a n d c e m e n t, s p e c i a l c h e m i c a l s a r e u s e d in J a p a n to f i x p o l l u t a n t s w i t h i n t r e a t e d s l u d g e s o n h a r b o r b o t t o m s. S w e d i s h p r a c t i c e a p p e a r s t h u s f a r t o h a v e b e e n l i m i t e d to i n l a n d p r o j e c t s in s oft, s e n s i t i v e c l a y s. M u c h of t h e w o r k in J a p a n h a s b e e n in w a t e r f r o n t a n d h a r b o r a r e a s a n d d o n e u s i n g l a r g e, b a r g e - m o u n t e d p l a n t s. S m a l l d i a m e t e r l i m e c o l u m n s (80 to 500 mm) s p a c e d a t 0.5 m to 3 m h a v e b e e n u s e d in A u s t r i a for s l o p e s t a b i l i z a t i o n as s h o w n in Fig. 33 (Brandtl, 1973). W h e n q u i c k l i m e (CaO) is u s e d as t h e s t a b i l i z e r t h e h e a t of h y d r a t i o n c a n b e s u b s t a n t i a l, a n d t h e d r y i n g of t h e s u r r o u n d i n g g r o u n d d u e t o this a n d to t h e c o n s u m p t i o n o f w a t e r b y h y d r a t i o n c a n b e s i g n i f i c a n t. A d m i x t u r e c o n t e n t s a r e o f t h e s a m e o r d e r (5 to 15 p e r c e n t b y d r y s o i l w e i g h t ) as f o r m o r e c o n v e n t i o n a l l i m e a n d c e m e n t s t a b i l i z a t i o n. B e c a u s e t h e s o i l s b e i n g t r e a t e d h a v e s u c h h i g h w a t e r contents, t h e f i n a l s t r e n g t h s a f t e r t r e a t m e n t w i l l b e m u c h l e s s t h a n t h o s e for l i m e a n d c e m e n t - t r e a t e d s o i l s l i s t e d in T a b l e s V I a n d VII. T h e y w i l l, n o n e t h e l e s s, b e m a n y t i m e s g r e a t e r t h a n t h a t of t h e u n t r e a t e d soil. R e l a t i o n s h i p s b e t w e e n u n c o n f i n e d c o m p r e s s i v e s t r e n g t h a n d w a t e r c o n t e n t for f o u r J a p a n e s e 536

29 Fig. 32 E x a m p l e o f a D e e p M i x i n g B i t u s e d in J a p a n Fig. 30 I m p r o v e d F o u n d a t i o n S o i l s f o r L a r g e T V T o w e r,., ( M i n k o v e t al.,1980) Fig. 33 S l o p e S t a b i l i z a t i o n U s i n g L i m e C o l u m n s a n d D r a i n a g e s o i l s t r e a t e d w i t h 10 p e r c e n t c e m e n t a r e s h o w n in Fig. 34. F o r a n o r m a l l y c o n s o l i d a t e d c l a y f r o m S w e d e n t h e s t r e n g t h i n c r e a s e d f r o m 2 to 7 t i m e s i m m e d i a t e l y a f t e r m i x i n g w i t h 6 a n d 12 p e r c e n t q u i c k l i m e a n d i n c r e a s e d t o 13 to 8 2 t i m e s the i n i t i a l s t r e n g t h o f a b o u t 10 k P a a f t e r 1.3 y e a r s. T h e i n i t i a l w a t e r c o n t e n t w a s a b o u t 60 p e r c e n t. S t r e n g t h i n c r e a s e s o f 10 to 20 t i m e s t h e u n t r e a t e d v a l u e a r e p e r h a p s t y p i c a l. C o m p r e s s i b i l i t y d e c r e a s e s a c c o m p a n y t h e s t a b i l i z a t ion. T h e r a t e of h a r d e n i n g w i l l be i n f l u e n c e d b y g r o u n d t e m p e r a t u r e. B r o m s a n d B o w m a n (1979a) n o t e t h a t t y p i c a l l y t h e c l a y i n l i m e c o l u m n s is 100 to t i m e s m o r e p e r m e a b l e t h a n in the u n t r e a t e d s t a t e. A s a c o n s e q u e n c e t h e c o l u m n s c a n a c t as v e r t i c a l d r a i n s, t h u s a c c e l e r a t i n g s e t t l e m e n t s. M e t h o d s f o r d e s i g n u s i n g l i m e c o l u m n s h a v e b e e n p r o p o s e d (Broms a n d B o w m a n, 1979a, b) f o r s e t t l e m e n t a n a l y s i s a n d b e a r i n g c a p a c i t y o f f o u n d a t i o n s a n d for t h e d e s i g n o f d e e p t r e n c h e s in i m p r o v e d g r o u n d. Fi g. 31 M a n u f a c t u r e o f a L i m e C o l u m n U s i n g S w e d i s h S y s t e m T H E R M A L S T A B I L I Z A T I O N I n t r o d u c t i o n B o t h h e a t i n g a n d f r e e z i n g c a n be u s e d for s o i l i m p r o v e m e n t. H e a t i n g f i n e - g r a i n e d s o i l s to m o d e r a t e t e m p e r a t u r e s ; e.g., h i g h e r t h a n 100 C, 537

30 t i o n s o f h e a t f l o w s a n d d e s i g n of h e a t i n g or r e f r i g e r a t i o n s y s t e m s a n d s t r u c t u r a l a n a l y s e s d e p e n d e n t o n t h e s t r e n g t h a n d s t r e s s - s t r a i n - t i m e p r o p e r t i e s o f t h e t r e a t e d g r o u n d. T h e r m a l A n a l y s e s T h e r m a l c o m p u t a t i o n s a r e r e q u i r e d to d e t e r m i n e h e a t i n g o r r e f r i g e r a t i o n r e q u i r e m e n t s, z o n e s of i n f l u e n c e, t r e a t m e n t t i m e s, t e m p e r a t u r e d i s t r i b u t i o n s, etc. H e a t f l o w a n a l y s e s c a n be d o n e in m u c h t h e s a m e w a y as c a n s e e p a g e a n d c o n s o l i d a t i o n a n a l y s e s. In t h e r m a l s t u d i e s, h o w e v e r, t h e b e h a v i o r m a y be d o m i n a t e d b y t h e l a t e n t h e a t of f u s i o n o f w a t e r o n f r e e z i n g a n d t h e h e a t of v a p o r i z a t i o n of w a t e r o n h e a t i n g a b o v e 100 C. G r o u n d w a t e r f l o w i n t o a n d o u t of t h e z o n e b e i n g t r e a t e d c a n h a v e a d o m i n a t i n g i n f l u e n c e. A n a l y t i c a l p r o c e d u r e s a n d c o m p u t e r c o d e s a r e a v a i l a b l e f o r t h e r m a l c o m p u t a t i o n s. M o s t a p p e a r t o h a v e b e e n d e v e l o p e d f o r a n a l y s i s o f g r o u n d f r e e z i n g, b u t s h o u l d at l e a s t a p p r o x i m a t e l y be a p p l i c a b l e to h e a t i n g, p r o v i d e d d i s t i n c t i o n is m a d e b e t w e e n l a t e n t h e a t a n d h e a t o f v a p o r i z a t i o n. A c o m p l i c a t i n g f a c t o r in t h e c a s e of h e a t i n g is v a p o r p h a s e t r a n s p o r t o f h e a t a n d w a t e r a t t e m p e r a t u r e s a b o v e 100 C. P r o c e d u r e s f o r t h e r m a l a n a l y s e s f o r g r o u n d f r e e z i n g a r e p r e s e n t e d b y S a n g e r (1968), S h u s t e r (1972), H a s h e m i a n d S l i e p c e v i c h (1973), T s y t o v i c h (1975), a n d S a n g e r a n d S a y l e s (19 79). F ig. 34 W ater Content - % U n c o n f i n e d C o m p r e s s i v e S t r e n g t h as a F u n c t i o n o f W a t e r C o n t e n t f o r F o u r J a p a n e s e S o i l s T r e a t e d w i t h C e m e n t ( C o u r t e s y of H. H o r i u c h i ) c a n c a u s e d r y i n g a n d s t r e n g t h i n c r e a s e if s u b s e q u e n t r e w e t t i n g is p r e v e n t e d. H e a t i n g to t e m p e r a t u r e s in t h e r a n g e o f 600 C to 1000 C c a n p r o d u c e s i g n i f i c a n t p e r m a n e n t p r o p e r t y i m p r o v e m e n t s, i n c l u d i n g d e c r e a s e in w a t e r s e n s i t i v i t y, s w e l l i n g, a n d c o m p r e s s i b i l i t y, a n d i n c r e a s e in s t r e n g t h. T r e a t m e n t a t s t i l l h i g h e r t e m p e r a t u r e s c a n r e s u l t in f u s i o n o f s o i l p a r t i c l e s. B e c a u s e f r o z e n w e t s o i l is f a r s t r o n g e r a n d l e s s p e r v i o u s t h a n u n f r o z e n g r o u n d, a r t i f i c i a l g r o u n d f r e e z i n g h a s a p p l i c a t i o n f o r t e m p o r a r y g r o u n d s t r e n g t h e n i n g a n d s u p p o r t. G r o u n d f r e e z i n g for s u p p o r t of o p e n e x c a v a t i o n s is a p a r t i c u l a r l y i m p o r t a n t a p p l i c a t i o n. P e r m a n e n t g r o u n d f r e e z i n g i n s t a l l a t i o n s a r e n o w s o m e t i m e s r e q u i r e d in a r c t i c a r e a s. B a c k - f r e e z i n g a n d m a i n t e n a n c e of f r o z e n s o i l c o n d i t i o n s a r o u n d p i l e f o u n d a t i o n s in p e r m a f r o s t a n d m a i n t e n a n c e o f f r o z e n s o i l s u n d e r h e a t e d b u i l d i n g s o n p e r m a f r o s t a r e t w o e x a m p l e s. D e s i g n of t h e r m a l s t a b i l i z a t i o n i n v o l v e s two c l a s s e s of p r o b l e m s ; n a m e l y, t h e r m a l e v a l u a T h e t h e r m a l p r o p e r t i e s r e q u i r e d for a n a l y s e s c a n g e n e r a l l y b e e s t i m a t e d w i t h i n r a t h e r n a r r o w l i m i t s f o r i n o r g a n i c s o i l s if t h e w a t e r c o n t e n t is k n o w n. T h e t h e r m a l c o n d u c t i v i t y, k, is u s u a l l y in t h e r a n g e o f to.3.5 W / m K. V a l u e s for f r o z e n a n d u n f r o z e n s o i l c a n be o b t a i n e d f r o m Fig. 35. T h e v o l u m e t r i c h e a t s ; i.e., t h e h e a t c o n t e n t p e r u n i t v o l u m e, c a n be d e t e r m i n e d f r o m t h e h e a t c a p a c i t i e s of t h e c o n s t i t u e n t s, w h i c h are: M a t e r i a l W a t e r, C, w Ice, Ci a c c o r d i n g to S o i l M i n e r a l s, Cm C u = Y Td -, f o r u n f r o z e n s o i l a n d / C w \ ( =. * ) / 'w \ V C m + TÏÏÔ ) H e a t C a p a c i t y (J/kq K) (24) (25) f o r f r o z e n soils, in w h i c h is t h e d r y d e n s i t y ( k g / m 3) a n d w is t h e w a t e r c o n t e n t in p e r c e n t. T h e l a t e n t h eat, L, for t h e p h a s e c h a n g e of w a t e r to i c e is 333 x J / k g. T h u s, f o r f r e e z i n g o r t h a w i n g s o i l t h e l a t e n t heat, L, is L ( Ï W > ( J / m 3) (26) F o r p h a s e c h a n g e s o n b o i l i n g, t h e h e a t o f v a p o r i z a t i o n, V, o f w a t e r is x l O 3 J / k g. So 538

31 h e a t i n g for s o i l s t a b i l i z a t i o n is t h e h i g h e n e r g y c ost. F i e l d M e t h o d s f o r D e e p S t a b i l i z a t i o n b y H e a t i n g In t h e m e t h o d d e v e l o p e d b y L i t v i n o v (1960) a b u r n e r is p l a c e d in a p l u g a t t h e t o p o f a s e a l e d b o r e h o l e. C o m p r e s s e d a i r a n d f u e l a r e i n j e c t e d u n d e r p r e s s u r e, a n d t h e t e m p e r a t u r e a n d c o m b u s t i o n p r o d u c t s c a n be c o n t r o l l e d. T h e s y s t e m is s h o w n s c h e m a t i c a l l y in Fig. 36. In a p p l i c a t i o n s e v e r a l b o r e h o l e s a r e c o n n e c t e d to a c e n t r a l a p p a r a t u s a n d f i r e d s i m u l t a n e o u s l y. Fig. 35 T h e r m a l C o n d u c t i v i t y o f S o i l ( A d a p t e d f r o m K e r s t e n, 1949) f o r v a p o r i z a t i o n o f w a t e r i n soil V s = V ( I W ) l 'd <2 7 > A p p l i c a t i o n s o f S t a b i l i z a t i o n b y H e a t i n g W i t h a f e w e x c e p t i o n s ; e.g., H i l l (1934), d e e p t r e a t m e n t b y h e a t i n g h a s b e e n u t i l i z e d p r i m a r i l y in E a s t e r n E u r o p e a n d t h e U S S R. H e a t i n g has b e e n u s e d s u c c e s s f u l l y to s t a b i l i z e l a n d s l i d e s a n d i m p r o v e c o l l a p s i n g s o i l s u n d e r e x i s t i n g s t r u c t u r e s (Beles a n d S t a n c u l e s c u, 1958), c o n s t r u c t a s t r u c t u r a l m a t for f o u n d a t i o n s u p p o r t (Kurnakov, 1972), f o r m v i t r i f i e d p i l e s in p l a c e, a n d r e d u c e d l a t e r a l s t r e s s e s o n r e t a i n i n g w a l l s a n d e m b e d d e d s t r u c t u r e s ( J u r d a n o v, 1978). B o t h c o m b u s t i o n m e t h o d s (Litvinov, 1960; L i t v i n o v e t al., 1979; K u r n a k o v, 1972) a n d e l e c t r i c a l m e t h o d s ( J u r d a n o v, 1978) a r e u s e d as h e a t s o u r c e s. S o m e i n v e s t i g a t i o n o f m i c r o w a v e d r y i n g ( S h i b a k o v a, 1975) a n d s o i l f u s i o n b y l a s e r b e a m ( Rom e t a l., 1977) h a s b e e n m a d e, b u t t h e s e t e c h n i q u e s a r e s t i l l in t h e e x p e r i m e n t a l stage. M o s t s u c c e s s f u l a p p l i c a t i o n s h a v e b e e n to p a r t l y s a t u r a t e d f i n e - g r a i n e d s o i l s s u c h as c o l l a p s i b l e l o e s s. A s i g n i f i c a n t g a s p e r m e a b i l i t y is d e s i r a b l e t o p e r m i t b o t h t h e r e m o v a l o f w a t e r v a p o r a n d t h e i n j e c t i o n o f s t a b i l i z i n g c o m p o u n d s w h i c h a r e s o m e t i m e s u s e d. H e a t i n g h a s b e e n f o u n d to b e a b o u t as e c o n o m i c a l as p r e - w e t t i n g w i t h b l a s t i n g for t r e a t m e n t o f l o e s s in t h e USSR. B o t h o f t h e s e m e t h o d s a r e g e n e r a l l y l e s s e x p e n s i v e t h a n p i l e s o r c a i s s o n s f o r t r e a t m e n t d e p t h s u p to 12 m ( B a g d a s a r o v e t al., 1977). P r o b a b l y t h e m o s t i m p o r t a n t f a c t o r l i m i t i n g t h e a p p l i c a t i o n of Fig. 36 S c h e m e for D e e p T h e r m a l S t a b i l i z a t i o n ( L i t v i n o v, 1960) 1. C o m p r e s s o r ; 2. C o l d A i r P i p e l i n e ; 3. L i q u i d F u e l C o n t a i n e r ; 4. P r e s s u r i z e d F u e l Pump; 5. Fuel P i p e L i n e ; 6. F i l t e r s ; 7. N o z z l e ; 8. C o m b u s t i o n C h a m b e r ; 9. B o r e Hole; 10. S t a b i l i z e d Zone. T h e a i r a n d g a s p r e s s u r e is t y p i c a l l y 25 to 50 p e r c e n t a b o v e a t m o s p h e r i c. S o i l h e a t i n g r e s u l t s f r o m i n f i l t r a t i o n of c o m p r e s s e d h o t a i r a n d c o m b u s t i o n p r o d u c t s as w e l l as b y c o n d u c t i o n. T e m p e r a t u r e s s h o u l d be k e p t b e l o w t h e s o i l fusion t e m p e r a t u r e to p r e v e n t p o r e b l o c k a g e. If o n l y a t m o s p h e r i c p r e s s u r e is m a i n t a i n e d in the b o r e h o l e, t h e n a s u b s t a n t i a l l y s m a l l e r d e p t h a n d v o l u m e of t r e a t e d s o i l r e s u l t. G a s t e m p e r a t u r e s r a n g i n g f r o m a b o u t 800 C for an a i r : f u e l r a t i o of 3.5 t o 2800 C for a r a t i o of 1.0 c a n be a c h i e v e d. T o t r e a t a c o l u m n of soil 1.5 to 2.5 m in d i a m e t e r to a d e p t h of 8 to 10 m r e q u i r e s 8 t o 10 days. S t a b i l i z a t i o n p r o c e e d s d u r i n g this p e r i o d b y p r o g r e s s i v e l y l o c a t i n g t h e f l a m e d e e p e r in t h e b o r e h o l e w h i l e the c o m b u s t i o n c h a m b e r r e m a i n s f i x e d a t the surface. 539

32 B e c a u s e of d e p t h l i m i t a t i o n s, t h e r m a l i n e f f i c i e n c i e s, a n d s a f e t y h a z a r d s, t h e p r o c e d u r e w a s m o d i f i e d r e c e n t l y ( L i t v i n o v et a l., 1979) so t h a t t h e b u r n e r c a n b e l o w e r e d i n t o t h e borehole. S t a b i l i z a t i o n is c o n d u c t e d in s e c t i o n s f r o m the b o t t o m up. P r e t r e a t m e n t o f t h e b o r e h o l e by b l o w i n g in a i r u n d e r p r e s s u r e (200 to 300 kpa) c a n i n c r e a s e t h e g a s p e r m e a b i l i t y b y a f a c t o r o f 3 to 5. D e p t h s of t r e a t m e n t of m o r e t h a n 20 m h a v e b e e n o b t a i n e d b y t h i s m e t h o d. K u r n a k o v (1972) r e p o r t s its a p p l i c a t i o n to f o r m a s t r u c t u r a l p a d v a r y i n g b e t w e e n 7 m a n d 16 m in t h i c k n e s s a n d c o v e r i n g an a r e a o f 3000 m 2. A n a l t e r n a t i v e f o r i n - s i t u h e a t i n g u s e s e l e c t r i c h e a t e r s r a t h e r t h a n c o m b u s t i o n ( J u r d a n o v, 1978). In o n e s y s t e m c o m p r e s s e d a i r is b l o w n t h r o u g h an e l e c t r i c h e a t e r a t t h e t o p of a b o r e h o l e. T e m p e r a t u r e s f r o m 500 C to 1200 C c a n b e a c h i e v e d. In a n o t h e r, e l e c t r i c h e a t e r s a r e i n s e r t e d in the b o r e h o l e. S o i l a d j a c e n t t o t h e b o r e h o l e c a n be s i n t e r e d to f o r m a s t r u c t u r a l m e m b e r. B y this m e a n s p i l e s, w a l l s, a n d s t r u c t u r a l m a t s c a n be f o r m e d. I n s e r t e d e l e c t r i c h e a t e r s c a n e f f e c t i v e l y f u s e a n d s i n t e r s o i l s r e g a r d l e s s o f w a t e r c o n t e n t o r g a s p e r m e a b i l i t y. P r o p e r t i e s o f H e a t - T r e a t e d S o i l s C h a n g e s o f p r o p e r t i e s of c o l l a p s i b l e l o e s s s o i l t r e a t e d b y t h e c o m b u s t i o n m e t h o d c a n b e s u b s t a n tial. R e s u l t s f r o m s e v e r a l s i t e s, s u m m a r i z e d by L i t v i n o v (1960), i n d i c a t e d a n a p p r o x i m a t e d o u b l i n g o f f r i c t i o n a n g l e, o r d e r of m a g n i t u d e i n c r e a s e in c o h e s i o n i n t e r c e p t, a n d f i v e - f o l d d e c r e a s e in c o m p r e s s i b i l i t y. T h e r e s u l t s in a n y c a s e d e p e n d s t r o n g l y o n i n i t i a l c o n d i t i o n s a n d f i r i n g t e m p e r a t u r e. R e c o m m e n d e d m i n i m u m t r e a t m e n t t e m p e r a t u r e s h a v e b e e n g i v e n b y J u r d a n o v (1978) to a c h i e v e the p r o p e r t i e s r e q u i r e d f o r d i f f e r e n t a p p l i c a t i o n s. P r o p o s e d v a l u e s a r e g i v e n in T a b l e VIII. C o s t of H e a t T r e a t m e n t T A B L E V I I I M i n i m u m H e a t T r e a t m e n t T e m p e r a t u r e s f o r D i f f e r e n t A p p l i c a t i o n s ( A d a p t e d f r o m J u r d a n o v, 1978) P u r p o s e of H e a t i n g R e d u c t i o n o f L a t e r a l P r e s s u r e E l i m i n a t i o n o f C o l l a p s e P r o p e r t i e s (loess) M i n i m u m T r e a t m e n t T e m p e r a t u r e ( C) C o n t r o l F r o s t H e a v e 500 M a s s i v e C o l u m n C o n s t r u c t i o n B e l o w F r o s t D e p t h M a n u f a c t u r e of B u i l d i n g M a t e r i a l s A l t h o u g h h e a t t r e a t m e n t h a s p r o v e n e c o n o m i c a l for s t a b i l i z a t i o n of c o l l a p s i b l e l o e s s in t h e U S S R in c o m p a r i s o n w i t h o t h e r m e t h o d s for s o i l i m p r o v e m e n t a n d f o u n d a t i o n s y s t e m s, its e c o n o m i c f e a s i b i l i t y in o t h e r p a r t s of the w o r l d a p p e a r s n o t t o h a v e b e e n t h o r o u g h l y e v a l u a t e d. F u e l a n d e n e r g y c o s t s w i l l be a m a j o r f a ctor, a n d t h e i r c o n t i n u i n g r i s e is n o t l i k e l y t o l e a d to a n y i n c r e a s e in c o m p e t i t i v e n e s s for t h e m e t h o d. I n g l e s a n d M e t c a l f (1973) p r o p o s e a n e q u a t i o n for e s t i m a t i o n of f u e l use, F, p e r u n i t v o l u m e of s t a b i l i z e d soil: ( 6. 4 w y, Ty ) T7> _ ^ Q /O O \ in w h i c h w is the m o i s t u r e c o n t e n t ( p e r c e n t ), y^ is soil d r y d e n s i t y, T is t h e b u r n i n g t e m p e r a t u r e a t t h e soil, a n d C^ is u n i t h e a t c a p a c i t y of t h e fuel (35% for o p e n b u r n i n g, 70% for closed b u r n i n g ). T h e b o r e h o l e s p a c i n g, d, for m i n i m u m fuel c o s t c a n t h e n b e c a l c u l a t e d u s i n g d = 2/ D /(ir-f-h ) (29) c c w h e r e D c is c o s t p e r u n i t l e n g t h f o r d r i l l i n g a n d H c is c o s t p e r u n i t w e i g h t o f fuel. G r o u n d S t a b i l i z a t i o n b y F r e e z i n g A r t i f i c i a l g r o u n d f r e e z i n g c a n b e a u s e f u l a n d v e r s a t i l e m e t h o d f o r t e m p o r a r y g r o u n d s u p p o r t o r g r o u n d w a t e r c o n t r o l, e s p e c i a l l y f o r s o f t g r o u n d c o n d i t i o n s, e x c a v a t i o n s d e e p e r t h a n a b o u t 7 to 8 m, a n d b e l o w t h e g r o u n d w a t e r t a b l e. D e t a i l e d r e v i e w o f a l l a s p e c t s o f g r o u n d f r e e z i n g is b e y o n d t h e s c o p e o f t h i s r e p o r t ; t h e r e f o r e, o n l y a b r i e f r e v i e w is g i v e n h e r e. M u c h i m p o r t a n t n e w i n f o r m a t i o n c a n be f o u n d in t h e P r o c e e d i n g s of t h e F i r s t I n t e r n a t i o n a l S y m p o s i u m o n G r o u n d F r e e z i n g h e l d a t R u h r U n i v e r s i t y, B o c h u m, G e r m a n y in T h e p a p e r b y B r a u n e t al. (1978) at t h a t c o n f e r e n c e p r e s e n t s a p r a c t i c a l o v e r v i e w of t h e m e t h o d, as d o e s a l s o S h u s t e r (1972). T h e p a p e r b y S a n g e r a n d S a y l e s (1979), a l s o a p a r t o f t h a t c o n f e r e n c e, p r o v i d e s d e t a i l s f o r the n e c e s s a r y t h e r m a l a n d s t r u c t u r a l a n a l y s e s a n d c o m p u t a t i o n s. T h e m o s t c r i t i c a l a s p e c t s t h a t m u s t b e c o n s i d e r e d to e n s u r e s a f e t y a n d s u c c e s s in g r o u n d f r e e z i n g ar e ( Shuster, 1972): 1. A c c u r a t e p o s i t i o n i n g of t h e f r e e z i n g e l e m e n t s 2. G r o u n d w a t e r f l o w a n d q u a l i t y 3. P o t e n t i a l g r o u n d m o v e m e n t s a n d p r e s s u r e s a c c o m p a n y i n g f r e e z i n g 4. L o n g t e r m s t r e n g t h a n d s t r e s s - s t r a i n p r o p e r t i e s of t h e f r o z e n g r o u n d. G r o u n d F r e e z i n g S y s t e m s A n u m b e r o f g r o u n d f r e e z i n g s y s t e m s a r e a v a i l a b l e as s h o w n in Fig. 37. A s a p r a c t i c a l m a t t e r these m a y b e r e d u c e d t o t w o b a s i c types: 1. E x p e n d a b l e r e f r i g e r a n t s y s t e m s u s i n g l i q u i d n i t r o g e n o r c a r b o n d i o x i d e in a n o p e n s y s t e m w h e r e t h e r e f r i g e r a n t is l o s t t o t h e a t m o s p h e r e a f t e r it h a s a b s o r b e d e n e r g y a n d v a p o r i z e d. T h e s e s y s t e m s c a n p r o d u c e r a p i d 540

33 Prime Mover Compressor Condensor Evaporator No plo n t, expendable solid refrigerant No p la n t, expendable liquid refrigerant Reliquefaction plant with in-situ cascaded 2nd stage Primary plont with in-situ evaporation Primary plant and in-situ pumped loop secondary coolant F i g. 37 A l t e r n a t i v e R e f r i g e r a t i o n A p p r o a c h e s ( S h u s t e r, 1972) g r o u n d f r e e z i n g in a m a t t e r of h o u r s h o w ever, t h e y a r e c o s t l y a n d d i f f i c u l t to c o n t r o l in t h e field. T h e y a r e g e n e r a l l y o n l y u s e d, t h e r e f o r e, u n d e r e m e r g e n c y c o n d i t i o n s. 2. C i r c u l a t i n g c o o l a n t s y s t e m s u s i n g a c o n v e n t i o n a l m e c h a n i c a l r e f r i g e r a t i o n p l a n t c o n n e c t e d to a c l o s e d c i r c u i t h y d r a u l i c s y s t e m in w h i c h t h e c o o l a n t flows. W i t h t h e s e s y s t e m s g r o u n d f r e e z i n g is s l o w e r - - r e q u i r i n g d a y s to w e e k s. T h e y are r e l a t i v e l y e a s y to c o n t r o l a n d i n e x p e n s i v e to o p e r a t e f o r long p e r i o d s. T h e p r i m a r y p l a n t w i t h i n - s i t u p u m p e d l o o p s e c o n d a r y c o o l a n t, Fig. 37, is t h e o n e t h a t is m o s t u sed. F r e e z e p i p e s p a c i n g s of 1 to 2 m are t y p i c a l. P i p e d i a m e t e r s a r e 100 to 150 m m w i t h i n t e r i o r f e e d p i p e s o f 35 to 55 mm. D e s i g n C o n s i d e r a t i o n s in G r o u n d F r e e z i n g In h e t e r o g e n e o u s g r o u n d t h e f r o z e n z o n e w i l l b e i r r e g u l a r in shape, as in Fig. 38. T h e s h a p e of t h e z o n e at s h a l l o w d e p t h w i l l be i n f l u e n c e d b y s e a s o n a l t e m p e r a t u r e v a r i a t i o n s u n l e s s s u r f a c e i n s u l a t i o n is used. F o r a g i v e n r e f r i g e r a n t t e m p e r a t u r e r e l a t i v e l y t h i n n e r f r o z e n g r o u n d w i l l n o r m a l l y o c c u r in s i l t s, c l a y s, a n d o r g a n i c s o i l s t h a n in s a n d s a n d g r a v e l s. As t h e s e are u s u a l l y t h e w e a k e r s t r a t a, s t r u c t u r a l d e s i g n may o f t e n be d i c t a t e d b y t h e s e m a t e r i a l s. T h e t h e r m a l e n e r g y a n d t i m e r e q u i r e d to c o m p l e t e f r e e z i n g m a y be c a l c u l a t e d a p p r o x i m a t e l y for h o m o g e n e o u s c o n d i t i o n s u s i n g t w o - d i m e n s i o n a l h e a t c o n d u c t i o n t h e o r y. F o r h e t e r o g e n e o u s p r o files, u n u s u a l g e o m e t r y, a n d n o n u n i f o r m t h e r m a l l o a d s, f i n i t e e l e m e n t o r f i n i t e d i f f e r e n c e a n a l y s e s m a y be w a r r a n t e d. T h e m o s t i m p o r t a n t f a c t o r s g o v e r n i n g c o s t a r e t h e s i z e a n d s p a c i n g o f f r e e z i n g p i p e s (Shuster, 1972). Fig. 39 c a n b e u s e d for e s t i m a t i o n of t h e t i m e r e q u i r e d to f r e e z e to a r a d i u s R for f r e e z e p i p e s of r a d i u s r Q. R e l a t i v e s p a c i n g s, R ', g r e a t e r t h a n 15 a r e n o t n o r m a l l y used. W i t h o u t p r o p e r f i e l d c o n t r o l o f a f i e l d l i q u i d n i t r o g e n f r e e z i n g p r o c e s s, t h e p o t e n t i a l t i m e s a v i n g s s h o w n in Fig. 39 m a y n o t b e r e a l i z e d. A p p r o x i m a t e l y, t h e e n e r g y r e q u i r e d t o f r e e z e t h e g r o u n d in K c a l / m 3 w i l l b e b e t w e e n 2200 a n d 2800 t i m e s t h e w a t e r c o n t e n t in p e r c e n t W i t h c i r c u l a t i n g c o o l a n t s y s t e m s s u c c e s s f u l f r e e z i n g m a y n o t b e p o s s i b l e i f t h e l a t e r a l r a t e o f g r o u n d w a t e r f l o w e x c e e d s 1.5 m / d a y. F l o w s as h i g h as 50 m / d a y h a v e b e e n s t o p p e d u s i n g l i q u i d n i t r o g e n ; h o w e v e r, t h e p r o c e d u r e is c o s t l y (Braun e t al., 1978). T h e a d d i t i o n a l r e f r i g e r a t i o n l o a d i n t r o d u c e d b y f l o w i n g g r o u n d w a t e r c a n be e s t i m a t e d a n d s h o u l d b e a c c o u n t e d for in s e l e c t i o n o f t h e r e f r i g e r a t i o n p l a n t. G r o u n d M o v e m e n t C o n s i d e r a t i o n s in F r e e z i n g B o t h e x p a n s i o n d u r i n g f r e e z i n g, o w i n g to the 9 p e r c e n t e x p a n s i o n of w a t e r a n d f o r m a t i o n o f i c e l e nses, a n d t h a w c o n s o l i d a t i o n a r e p o s s i b l e. N e i t h e r is l i k e l y to b e s i g n i f i c a n t for s a n d s 541

34 Relative values, MKH units: Frozen Frozen Creep Thermal Shear Conductivity Strength a n d g r a v e l s w h i c h c a n d r a i n as r a p i d l y as f r e e z i n g o c c u r s. In s i l t s a n d c l a y s, h o w e v e r, s i g n i f i c a n t m o v e m e n t s a r e p o s s i b l e. A p p r o x i m a t e c o m p u t a t i o n s, s u f f i c i e n t t o e n a b l e e v a l u a t i o n o f w h e t h e r or n o t a p o t e n t i a l p r o b l e m e x i s t s a n d t h e o r d e r of m a g n i t u d e o f m o v e m e n t s t h a t m a y o c c u r, a r e p o s s i b l e ( S h uster, 1972; R a d d a n d W o l f e, 1978; T a k a g i, 1978; K l e i n a n d J e s s b e r g e r, 1978; J o n e s a n d B r o w n, 1978; C h a m b e r l a i n a n d Gow, 1978). Fig. 38 E f f e c t o f H e t e r o g e n e o u s G r o u n d C o n d i t i o n s o n S h a p e o f F r o z e n Z o n e ( S h uster, 1972) D e f o r m a t i o n a n d S t r e n g t h C o n s i d e r a t i o n s in G r o u n d F r e e z i n g T h e l o n g t e r m s t r e n g t h a n d s t r e s s - s t r a i n c h a r a c t e r i s t i c s o f f r o z e n g r o u n d d e p e n d m a i n l y o n ice c o n t e n t, t e m p e r a t u r e, a n d d u r a t i o n o f l o a d i n g. T h e s h o r t t e r m s t r e n g t h u n d e r r a p i d l o a d i n g m a y b e 5 to 10 t i m e s g r e a t e r t h a n t h a t u n d e r s u s t a i n e d s t r e s s e s ; i.e., f r o z e n s o i l s a r e s u s c e p t i b l e to l a r g e c r e e p s t r e n g t h l o s s e s. T h e c o m p r e s s i o n s t r e n g t h in s h o r t - t e r m t e s t s a t l o w t e m p e r a t u r e s m a y b e u p to 20 M P a. T h e C o u l o m b e q u a t i o n c a n b e u s e d t o c h a r a c t e r i z e t h e c o n f i n i n g s t r e s s - d e p e n d e n c y o f f r o z e n soil. T h e d e f o r m a t i o n b e h a v i o r o f f r o z e n s o i l is v i s c o - p l a s t i c, a n d b o t h s t r e s s a n d t e m p e r a t u r e h a v e s i g n i f i c a n t i n f l u e n c e o n t h e s t r a i n at a n y time. T h e c r e e p c u r v e s in Fig. 40 for a f r o z e n s i l t y c l a y ( S a n g e r a n d S a y l e s, 1978) a r e i l l u s t r a t i v e o f t h e s e e f f e c t s. T h e o n s e t of the t h i r d s t a g e o f c r e e p r e p r e s e n t s t h e b e g i n n i n g of f a i l u r e. T h u s, t i m e t f c a n b e c o n s i d e r e d r e p r e s e n t a t i v e of t h e t i m e to f a i l u r e. F o r m a n y soils t h e r e l a t i o n s h i p b e t w e e n s t r e s s a n d t i m e to f a i l u r e c a n b e d e s c r i b e d by = a + b l o g t. (30) a f w h e r e p a r a m e t e r s a a n d b a r e f u n c t i o n s o f t e m p e r a t u r e. T h i s e q u a t i o n c a n b e u s e d w i t h a f a c t o r o f s a f e t y o n t i m e t o d e t e r m i n e m a x i m u m a l l o w a b l e s t r e s s. F o r e x a m p l e, if a n e x c a v a t i o n is to b e o p e n for a m o n t h, t h e u s e o f a y e a r f o r tf m a y b e r e a s o n a b l e (Sanger, 1968). V i a l o v ' s e q u a t i o n h a s b e e n f o u n d to f i t c r e e p d a t a w e l l. T h e c r e e p s t r a i n, e, a t a n y t i m e is g i v e n by (u(0+l) K w h e r e a is s t r e s s, 9 is d e g r e e s b e l o w f r e e z i n g, a n d m, X, u, a n d k a r e e x p e r i m e n t a l l y d e t e r m i n e d p a r a m e t e r s r e q u i r i n g s e t s of c r e e p t e s t s at t w o t e m p e r a t u r e s. Fig. 39 Relative Size of Zone to be Frozen, R '- No.of Units D e t e r m i n a t i o n o f R e q u i r e d F r e e z i n g T i m e ( S h u s t e r, 1972) I n p r a c t i c e t h e e v a l u a t i o n o f s t a b i l i t y o f f r o z e n s o i l m a s s e s, t h e p r e d i c t i o n o f c r e e p d e f o r m a t i o n, a n d t h e p o s s i b i l i t y o f c r e e p r u p t u r e a r e c o m p l e x p r o b l e m s. T h i s is b e c a u s e n o t o n l y m a y t h e r e be h e t e r o g e n e o u s g r o u n d a n d i r r e g u l a r g e o m e t r i e s, b u t a l s o t h e r e w i l l b e t e m p e r a t u r e a n d s t r e s s v a r i a t i o n s t h r o u g h o u t t h e f r o z e n s o i l m a s s. M o r e d e t a i l e d d i s c u s s i o n s of c r e e p a n d s t r e n g t h b e h a v i o r as it r e l a t e s t o g r o u n d f r e e z i n g for g r o u n d s u p p o r t p u r p o s e s c a n be f o u n d in V i a l o v (1962), S a n g e r (1968), S h u s t e r (1972), T s y t o v i c h (1975), S a n g e r a n d S a y l e s (1979) a n d T a k e g a w a e t al. (1979). 542

35 m e n t s a n d f u n c t i o n as d r a i n s for t h e s o f t soil. T h e y c a n be u s e d a l s o t o r e s i s t s h e a r in h o r i z o n t a l a n d i n c l i n e d d i r e c t i o n s. S a n d c o l u m n s i n s t a l l e d b y the C o m p o z e r s y s t e m a r e u s e d f o r t h e s a m e p u r p o s e s in J a p a n. R o o t p i l e s o r m i c r o - p i l e s a r e s m a l l d i a m e t e r p i l e s (75 t o 250 mm) o f c o n c r e t e c a s t in p l a c e, u s u a l l y w i t h a r e i n f o r c i n g b a r i n the c e n t e r. T h e y a r e i n s t a l l e d in g r o u p s w i t h i n d i v i d u a l p i l e s b o t h v e r t i c a l a n d i n c l i n e d. T h e y c a n b e u s e d b o t h f o r s u p p o r t o f s t r u c t u r e s a n d f o r s t a b i l i z a t i o n o f t h e i n c l u d e d s o i l a g a i n s t m o v e m e n t a n d l o s s of s t a b i l i t y. S o i l n a i l i n g c o n s i s t s of a s e r i e s o f r e i n - f o r c i n g b a r s g r o u t e d i n t o t h e g r o u n d to b e s u p p o r t e d. A n i l l u s t r a t i o n of s o i l n a i l i n g f o r s u p p o r t of a n e x c a v a t e d s l o p e is g i v e n i n Fig. 41. R e i n f o r c e d e a r t h is a c o n s t r u c t e d c o m p o s i t e m a t e r i a l c o n s i s t i n g of a l t e r n a t i n g l a y e r s of c o m p a c t e d b a c k f i l l a n d t e n s i l e r e i n f o r c i n g m a t e r i a l. B o t h m e t a l s a n d g e o t e x t i l e s a r e u s e d as r e i n f o r c e m e n t s. R e i n f o r c e d e a r t h is u n i q u e a m o n g t h e s e four t e c h n i q u e s in t w o w ays: Fig. 4 0 S O I L R E I N F O R C E M E N T In t r o d u c t i o n Time, t - hr C r e e p C u r v e s for a F r o z e n O r g a n i c S i l t y C l a y ( S a n g e r a n d S a y l e s, 1978) O f t h e m e t h o d s o f s o i l i m p r o v e m e n t a n d g r o u n d s t r e n g t h e n i n g, n o n e h a v e b e e n so i n t e n s i v e l y s t u d i e d a n d a d v a n c e d in a p p l i c a t i o n in t h e p a s t s e v e r a l y e a r s as h a s s o i l r e i n f o r c e m e n t. B o t h t h e m a n u f a c t u r e o f c o m p o s i t e c o n s t r u c t i o n m a t e r i a l s o f e a r t h w i t h r e i n f o r c i n g i n c l u s i o n s a n d g r o u n d r e i n f o r c e m e n t i n - s i t u a r e n o w w i d e l y u sed. M a n y o f t h e c u r r e n t a n d p o t e n t i a l a p p l i c a t i o n s a r e d e s c r i b e d b y B a r t o s (1979). S e v e r a l of the s o i l i m p r o v e m e n t m e t h o d s a l r e a d y d i s c u s s e d in t h i s r e p o r t a r e f o r m s o f s o i l r e i n f o r c e m e n t ; e.g., s a n d a n d g r a v e l c o m p a c t i o n p i l e s ; p i l e s, p i e r s, a n d w a l l s c o n s t r u c t e d b y d e e p m i x i n g m e t h o d s ; g r o u n d s t r e n g t h e n i n g b y h e a t i n g or f r e e z i n g. T h e r e a r e at l e a s t f o u r o t h e r t y p e s o f s o i l r e i n f o r c e m e n t t h a t a r e u s e d at t h e p r e s e n t time: r e i n f o r c e d e a r t h, s o i l n a i l i n g, r o o t p i l e s, a n d s t o n e c o l u m n s. T h e a r r a n g e m e n t o f r e i n f o r c e m e n t s a n d t h e i r f u n c t i o n s a r e d i f f e r e n t f o r e a c h o f them, as m a y b e s e e n f r o m T a b l e IX. A p p l i c a t i o n s for t h e d i f f e r e n t r e i n f o r c i n g s y s t e m s a r e s u m m a r i z e d in T a b l e X. S t o n e c o l u m n s a r e c o m p a c t e d c o l u m n s o f g r a v e l o r c r u s h e d r o c k i n s t a l l e d i n t o s o f t soils. D i a m e t e r s a r e u s u a l l y in t h e r a n g e o f 0.6 t o 1.0 m. T h e y p r o v i d e v e r t i c a l s u p p o r t f o r o v e r l y i n g s t r u c t u r e s o r e m b a n k 1. T h e r e i n f o r c e m e n t s a r e u s e d to c a r r y t e n s i o n o n l y 2. It is a c o m p o s i t e m a t e r i a l in w h i c h t h e s o i l a n d r e i n f o r c e m e n t s a r e b u i l t u p in s u c c e s s i v e l a y e r s. T h e o t h e r s a r e u s e d to r e s i s t s t r e s s e s in at l e a s t t w o m o d e s, a n d t h e y a r e u s e d to s t r e n g t h e n t h e g r o u n d i n - s i t u. A c o m p r e h e n s i v e d e s c r i p t i o n o f t h e c o n s t r u c t i o n a n d c h a r a c t e r i s t i c s o f c o m p r e s s i o n r e i n f o r c e m e n t e l e m e n t s is g i v e n by the C o m m i t t e e o n P l a c e m e n t a n d I m p r o v e m e n t o f S o i l s (1978). G r o u n d a n c h o r s a n d t i e - b a c k s y s t e m s a r e o u t s i d e t h e s c o p e o f t h i s r e p o r t. S t o n e a n d S a n d C o l u m n s M o d e r n t e c h n i q u e s f o r t h e c o n s t r u c t i o n o f c o m p a c t e d g r a v e l c o l u m n s in s o f t s o i l s w e r e d e v e l o p e d in G e r m a n y s t a r t i n g i n t h e l a t e 's. M e t h o d s f o r i n s t a l l a t i o n of d e n s e l y c o m p a c t e d s a n d c o l u m n s w e r e d e v e l o p e d c o n c u r r e n t l y in J a p a n. C o n s t r u c t i o n of s a n d p i l e s in l o o s e sand b y t h e V i b r o - C o m p o z e r m e t h o d w a s d e s c r i b e d in an e a r l i e r s e c t i o n a n d i l l u s t r a t e d b y Fig. 5. E s s e n t i a l l y t h e s a m e p r o c e d u r e is u s e d for i n s t a l l a t i o n of s a n d p i l e s in s o f t clays. M o s t s t o n e c o l u m n i n s t a l l a t i o n s a r e m a d e u s i n g the v i b r o - r e p l a c e m e n t m e t h o d in a m a n n e r s i m i l a r to v i b r o f l o t a t i o n, as s h o w n e a r l i e r in Fig. 4. A c y l i n d r i c a l v e r t i c a l h o l e is m a d e by a v i b r a t i n g p r o b e p e n e t r a t i n g b y j e t t i n g a n d u n d e r its o w n w e i g h t. In s o m e c a s e s a d r y p r o c e s s w i t h o u t w a t e r j e t s is u sed. G r a v e l b a c k f i l l is d u m p e d i n t o t h e h o l e in i n c r e m e n t s of 0.4 t o 0.8 m and c o m p a c t e d b y t h e p r o b e w h i c h s i m u l t a n e o u s l y d i s p l a c e s t h e m a t e r i a l r a d i a l l y i n t o t h e s o f t soil. T h e d i a m e t e r of t h e r e s u l t i n g c o l u m n c a n be estim a t e d f r o m t h e r o c k c o n s u m p t i o n. It w i l l usually b e in t h e r a n g e of 0.6 to 1.0 m. L a r g e r d i a m e t e r c o l u m n s c a n b e f o r m e d b y c o u p l i n g v i b r a t o r s t o g e t h e r. C o l u m n l e n g t h s u p to 20 m h a v e b e e n i n s t a l l e d. T h e s o f t e r t h e g r o u n d the l a r g e r t h e d i a m e t e r. In s i t u a t i o n s w h e r e s o f t 543

36 TABLE IX T y p e o f E a r t h R e i n f o r c e m e n t a n d R e i n f o r c e m e n t F u n c t i o n s ( S c h l o s s e r a n d J u r a n, 1979) R e i n f o r c e m e n t M a j o r T y p e f u n c t i o n o r ' ' - - ^ ^ ^ r e i n f o r c e m e n t R e i n f o r c e d E a r t h N a i l i n g R o o t P i l e s T e n s i o n * * * S t o n e C o l u m n s C o m p r e s s i o n * * S h e a r * F l e x u r e * T A B L E X A p p l i c a t i o n s o f S o i l R e i n f o r c e m e n t ( S c h l o s s e r a n d J u r a n, 1979) A p p l i c a t i o n R e i n f o r c e m e n t T y p e R e i n f o r c e d E a r t h N a i l i n g R o o t P i l e s S t o n e C o l u m n s B e a r i n g c a p a c i t y * *** * * S t a b i l i t y * * * ** * * S e t t l e m e n t M a g n i t u d e * * *** S e t t l e m e n t R a t e * * Phases of execution Grouted bars Shotcrete Fissure Bars in tension g r o u n d w o u l d o t h e r w i s e s q u e e z e in, t h e b a c k f i l l c a n b e i n t r o d u c e d t h r o u g h a s e p a r a t e p i p e a h e a d o f t h e p r o b e. G r a v e l p a r t i c l e s i z e s in the r a n g e o f 20 to 75 m m a r e t y p i c a l. S q u a r e or t r i a n g u l a r g r i d p a t t e r n s a r e u s e d w i t h c e n t e r - t o - c e n t e r c o l u m n s p a c i n g s o f 1.5 t o 3. 5 m. A n e n t i r e f o u n d a t i o n a r e a m a y b e c o v e r e d, w i t h a d d i t i o n a l c o v e r a g e a r o u n d t h e p e r i m e t e r t o i n c l u d e s t r e s s s p r e a d w i t h d e p t h. C o l u m n s m a y a l s o be u s e d in c l u s t e r s a n d r o w s to s u p p o r t f o o t i n g s a n d w a l l s. T h e c o l u m n s s h o u l d e x t e n d i n t o a f i r m e r s t r a t u m b e l o w. A b l a n k e t o f s a n d o r g r a v e l 0.3 m o r m o r e in t h i c k n e s s is u s u a l l y p l a c e d o v e r t h e top. T h i s b l a n k e t s e r v e s b o t h a s a d r a i n a g e l a y e r a n d to d i s t r i b u t e s t r e s s e s f r o m s t r u c t u r e s above. Fig. 41 E x a m p l e o f S o i l N a i l i n g for S t a b i l i z a t i o n of E x c a v a t e d S l o p e ( f r o m S c h l o s s e r a n d J u r a n, 1980) S t o n e a n d s a n d c o l u m n s y s t e m s in soft, c o m p r e s s i b l e s o i l s a r e s o m e w h a t l i k e p i l e f o u n d a t i o n s, e x c e p t t h a t p i l e c a p s, s t r u c t u r a l c o n n e c t i o n s, a n d d e e p p e n e t r a t i o n i n t o u n d e r l y i n g f i r m s t r a t a a r e n o t r e q u i r e d, a n d t h e s t o n e c o l u m n s are, of c o u r s e, m o r e c o m p r e s s i b l e. W h e n u s e d in l i e u of p i l e o r c a i s s o n f o u n d a t i o n s t h e s u p p o r t i n g c a p a c i t y a n d s e t t l e m e n t are o f p r i m a r y c o n c e r n. W h e n u s e d f o r s t a b i l i t y p u r p o s e s u n d e r e m b a n k m e n t s or in s l o p e s, as s h o w n in Fig. 42, t h e s h e a r s t r e n g t h of t h e c o l u m n s is of p r i m a r y i n t e r e s t. 544

37 T h e e f f e c t i v e n e s s a n d s u i t a b i l i t y of s t o n e columns for u s e in s o f t c l a y s o f h i g h s e n s i t i v i t y is o p e n t o s o m e d e b a t e b e c a u s e o f t h e d e t r i m e n t a l e f f e c t s o f t h e i n s t a l l a t i o n p r o c e s s o n s t r e n g t h ( B a u m a n n a n d B a u e r, 1974; D i s c u s s i o n, I n s t i t u t i o n of Civil E n g i n e e r s, 1976). 0 w h e r e is t h e u n d r a i n e d s h e a r s t r e n g t h o f the s o f t g r o u n d a n d F.S. is t h e f a c t o r o f s a f e t y. A v a l u e o f 3 is r e c o m m e n d e d f o r the F.S. T h e s e t t l e m e n t o f a s t o n e c o l u m n f o u n d a t i o n d e p e n d s o n c o l u m n s p a c i n g. A l o a d t e s t o n a s i n g l e c o l u m n w i t h i n a g r o u p w i l l o r d i n a r i l y g i v e a s e t t l e m e n t in t h e r a n g e of 5 to 10 m m u n d e r t h e d e s i g n load. E x p e r i e n c e a n d a n a l y s e s i n d i c a t e t h a t t h e s e t t l e m e n t of a l a r g e l o a d e d a r e a s u p p o r t e d b y s t o n e c o l u m n s w i l l be a b o u t 5 to 10 t i m e s g r e a t e r t h a n t his. E s t i m a t e d s e t t l e m e n t o f t r e a t e d g r o u n d as a f u n c t i o n o f soil s t r e n g t h a n d c o l u m n s p a c i n g is s h o w n in Fig. 43. T o t h e s e e s t i m a t e s s h o u l d b e a d d e d a n y a n t i c i p a t e d s e t t l e m e n t s c o n t r i b u t e d b y t h e u n d e r l y i n g s t r a t a. Fig. 42 S t o n e o r S a n d C o l u m n s U s e d to I m p r o v e S l o p e S t a b i l i t y A l t h o u g h s o m e d e s i g n e r s a s s u m e c o n s e r v a t i v e l y t h a t a l l t h e a p p l i e d f o u n d a t i o n l o a d s a r e c a r r i e d b y t h e c o l u m n s, t h e s t r e s s e s a r e s h a r e d b e t w e e n t h e m a n d t h e s u r r o u n d i n g s o f t g r o u n d in p r o p o r t i o n to the r e l a t i v e s t i f f n e s s of t h e t w o m a t e r i a l s, t h e c r o s s - s e c t i o n a l a r e a of t h e c o l u m n s a n d t h e i r s p a c i n g. A s t r e s s c o n c e n t r a t i o n r a t i o, n, m a y b e d e f i n e d as t h e r a t i o of v e r t i c a l s t r e s s in t h e c o m p a c t e d c o l u m n, a, to t h a t in t h e s o f t g r o u n d, ac S e v e r a l m e t h o d s for t h e d e t e r m i n a t i o n of t h e s u p p o r t i n g c a p a c i t y a n d l o a d - s e t t l e m e n t b e h a v i o r o f s t o n e c o l u m n f o u n d a t i o n s, r a n g i n g f r o m e x p e r i e n c e - b a s e d e m p i r i c a l e s t i m a t e s to s o p h i s t i c a t e d f i n i t e e l e m e n t a n a l y s e s, h a v e b e e n p r o p o s e d. U s e f u l g u i d e l i n e s a r e p r e s e n t e d by T h o r b u r n (1975) a n d t h e A S C E C o m m i t t e e o n P l a c e m e n t a n d I m p r o v e m e n t of S o i l s (1978). A n a l y t i c a l m e t h o d s a r e p r o p o s e d b y B a u m a n n a n d B a u e r (1974), H u g h e s a n d W i t h e r s (1974), P r i e b e (1976), Ba'laam e t al. (1977), A b o s h i e t a l. (1979), a n d G o u g h n o u r a n d B a y u k ( a ). In s p i t e o f the c o m p l e x i t y o f t h e l o a d t r a n s f e r m e c h a n i s m in a s t o n e c o l u m n f o u n d a t i o n a n d t h e n e e d f o r s i m p l i f y i n g a s s u m p t i o n s in a n a l y s i s, t h e r e s u l t s o b t a i n e d b y t h e s e v e r a l m e t h o d s a r e o f t e n in r e a s o n a b l e a g r e e m e n t w i t h e a c h o t h e r a n d w i t h f i e l d m e a s u r e m e n t s. F o r a n a l y s i s p u r p o s e s the e f f e c t i v e c o h e s i o n c' a n d f r i c t i o n a n g l e (Jig' of c o m p a c t e d s t o n e c o l u m n s c a n b e t a k e n a s 0 a n d 35 t o 40, r e s p e c t i v e l y. M o d u l u s v a l u e s in t h e r a n g e of 40 to 70 M N / m 2 a r e a p p r o p r i a t e. T h e l o a d c a p a c i t y o f a s t o n e o r s a n d c o l u m n is c o n t r o l l e d b y t h e p a s s i v e r e s i s t a n c e o f t h e soft s o i l t h a t c a n b e m o b i l i z e d to w i t h s t a n d r a d i a l b u l g i n g a n d b y t h e f r i c t i o n a n g l e o f t h e c o m p a c t e d m a t e r i a l in t h e c o l u m n. T h e r e q u i r e d m i n i m u m l e n g t h of c o l u m n i n s o f t s o i l c a n be e s t i m a t e d b a s e d o n t h e s h e a r i n g s t r e n g t h a l o n g the s i d e s a n d t h e e n d b e a r i n g c a p a c i t y. In p r a ctice, h o w e v e r, c o l u m n s a r e o r d i n a r i l y c a r r i e d t h r o u g h t h e s o f t l a y e r to a f i r m e r b e a r i n g l a y e r b e l o w in o r d e r to p r e v e n t e x c e s s i v e s e t t l e m e n t. Design v a l u e s o f 20 to 30 t o n s p e r c o l u m n a r e t y p i c a l f o r c o l u m n s in s o f t to m e d i u m s t i f f c l a y s. B o t h l i m i t a n a l y s e s ( H ughes a n d W i t h e r s, 1974) a n d e x p e r i e n c e (Thorburn, 1975) i n d i c a t e t h a t the a l l o w a b l e v e r t i c a l s t r e s s, a v, o n a s i n g l e c o l u m n c a n b e e x p r e s s e d b y n = a /a s c (33) A v a i l a b l e i n f o r m a t i o n ( Vautrain, 1977; Pilot, 1977; G o u g h n o u r a n d B a y u k, b ) ; A b o s h i et al, 1979; M u r a y a m a, p e r s o n a l c o m m u n i c a t i o n ) i n d i c a t e s t h a t n f a l l s in t h e r a n g e of 2 t o 6, w i t h v a l u e s o f 3 to 4 u s u a l. If A_ is t h e c r o s s s e c t i o n a l a r e a o f s t o n e o r s a n d c o l u m n, a n d A c is t h e p l a n a r e a o f c l a y p e r c o l u m n, t h e n (A + A ) a = A a + A a s c s s c c w h e r e a is t h e a v e r a g e a p p l i e d s t r e s s. A r e p l a c e m e n t r a t i o, a s, m a y be d e f i n e d as T h u s a = A / ( A + A ) s s s c a c = ct/ [1 + (n - 1 ) a ] = u c a = n a / [ 1 + (n - 1 ) a g ] = u s a (34) (35) (36) (37) T h e c o n s o l i d a t i o n s e t t l e m e n t, s, o f u n r e i n f o r c e d g r o u n d w o u l d b e s = m a H s w h e r e m s is t h e c o m p r e s s i b i l i t y a n d H is the l a y e r t h i c k n e s s. T h e c o n s o l i d a t i o n s e t t l e m e n t of t h e c o m p o s i t e f o u n d a t i o n, s', w o u l d be s ' = m a H = m p a H s c s c a n d t h e s e t t l e m e n t r e d u c t i o n r a t i o. S. w i l l be (38) (39) 25 Tf F.S. (32) B = U c = 1 / [ 1 + (n - 1) a g ] (40) 36. Volym e 4 545

38 1 <5 Ç <5 <b!,<b VS Co O à? Clay Strength Columns assumed resting on firm ground Immediate settlements and shear displacements neglected kn/m2 (0 4 tsf) kn/m2(0.2tsf) Stone Column Spacing -m Fig. 43 E f f e c t o f S t o n e C o l u m n s o n A n t i c i p a t e d F o u n d a t i o n S e t t l e m e n t ( G r e e n w o o d, 1970) a s s u m i n g t h a t t h e c l a y a n d c o l u m n s s e t t l e e q u a l a m o u n t s. E q u a t i o n (40) s h o w s, as w o u l d be e x p e c t e d, t h a t t h e h i g h e r t h e v a l u e s of s t r e s s c o n c e n t r a t i o n r a t i o a n d r e p l a c e m e n t r a t i o t h e g r e a t e r w i l l be t h e r e d u c t i o n in s e t t l e m e n t. A l t e r n a t i v e m e t h o d s f o r s e t t l e m e n t a n a l y s i s b a s e d o n t h e r a d i a l e x p a n s i o n a n d v e r t i c a l c o m p r e s s i o n of t h e c o l u m n a r e p r o p o s e d by H u g h e s e t al. (1975) a n d P r i e b e (1976). P r i e b e d e v e l o p e d c h a r t s e n a b l i n g t h e s i m p l e e s t i m a t i o n of s e t t l e m e n t r e d u c t i o n. D r a i n a g e t h r o u g h s a n d a n d g r a v e l c o l u m n s a c c e l e r a t e s s e t t l e m e n t s. B a l a a m e t al. (197 6) p r e s e n t e d a n a l y s i s m e t h o d s. G o u g h n o u r a n d B a y u k (1979a) s u g g e s t e d t h a t c o n v e n t i o n a l s a n d - d r a i n t h e o r y is s u i t a b l e f o r t i m e - s e t t l e m e n t c o m p u t a t i o n s. A n a l y s i s of t h e r e i n f o r c i n g e f f e c t of s t o n e and sa n d c o l u m n s in s t a b i l i t y a p p l i c a t i o n s o f the t y p e s h o w n in Fig. 42 is u s u a l l y d o n e o n t h e b a s i s of a c o m p o s i t e s h e a r s t r e n g t h b a s e d on t h e u n d r a i n e d s t r e n g t h of t h e c l a y, t h e t r a n s v e r s e s h e a r s t r e n g t h of t h e columns, a n d t h e r e p l a c e m e n t ratio. A s t h e s h e a r s t r e n g t h of t h e c o l u m n s d e p e n d s p r i m a r i l y o n t h e n o r m a l s t r e s s o n t h e s h e a r p l a n e, a n d t h i s s t r e s s is n o t r e a d i l y d e t e r m i n e d o w i n g to t h e c o m p l e x i t y of t h e c o l u m n - s o f t g r o u n d i n t e r a c t i o n s, a s s u m p t i o n s a n d a p p r o x i m a t i o n s a r e r e q u i r e d. B o t h P r i e b e (1978) a n d A b o s h i e t al. (1979) h a v e p r e s e n t e d m e t h o d s f o r m a k i n g t h e s e d e t e r m i n a t i o n s. T h e c o m p o s i t e s h e a r i n g r e s i s t a n c e t a t a n y p o i n t a l o n g t h e c i r c u l a r s l i d i n g s u r f a c e, Fig. 42, is o b t a i n e d b y s u m m i n g t h e s t r e n g t h s T s a n d T c f o r t h e c o l u m n a n d c l a y, r e s p e c t i v e l y (Aboshi e t a l., 1979). t = ( l - a s )xc + a s t g c o s a (41) S t r e n g t h x g is o b t a i n e d f r o m t g = p z tan<(>g c o s a (42) w h e r e p z is t h e v e r t i c a l s t r e s s o n t h e s l i d i n g s u r f a c e, g i v e n b y p = v 'z + a y (43) 's z s in w h i c h y ' z is t h e e f f e c t i v e o v e r b u r d e n p r e s s u r e of t h e c o l u m n i t s e l f a n d ctz y s is t h e i n c r e m e n t o f s t r e s s d u e to s u r f a c e l o a d i n g. y s is g i v e n b y e q u a t i o n (37), a n d ct2 is o b t a i n e d u s i n g e l a s t i c t h e o r y s t r e s s d i s t r i b u t i o n s. In t h e m e t h o d d e v e l o p e d _ b y P r i e b e (1978) c o m p o s i t e v a l u e s of <}> a n d c a r e u s e d, a n d t h e y are d e t e r m i n e d b y tan< > = m tan<(ig + (1 - m ) tamfij, (44) c = (1 - m) c (45) w h e r e c a n d 4>c a r e t h e s t r e n g t h p a r a m e t e r s of the u n i m p r o v e d s o i l m a s s. T h e p a r a m e t e r m is the r e l a t i v e s t r e s s d i s t r i b u t i o n b e t w e e n s o f t s o i l a n d c o l u m n d e f i n e d b y G r a p h s, b a s e d o n t h e r e p l a c e m e n t r a t i o, a g and t h e c o l u m n f r i c t i o n a n g l e, < >g a r e g i v e n b y P r i e b e f o r t h e r a p i d d e t e r m i n a t i o n o f m. A l t e r n a t i v e l y, it w o u l d s e e m r e a s o n a b l e to m a k e u s e o f e q u a t i o n s (36) a n d (37) a n d t h e f a c t t h a t n 546

39 is l i k e l y to b e in t h e r a n g e o f 3 to 4 to d e t e r m i n e a s u i t a b l e v a l u e o f m. W h e n s t o n e c o l u m n s w e r e p r o p o s e d f o r s u p p o r t of a l a r g e s e w a g e t r e a t m e n t p l a n t in C a l i f o r n i a, t h e r e w a s c o n c e r n a b o u t b o t h t h e a b i l i t y of the c o l u m n s to t r a n s m i t h o r i z o n t a l s h e a r a n d the i n t e g r i t y o f t h e c o l u m n s s h o u l d t h e s u r r o u n d i n g g r o u n d l i q u e f y in t h e e v e n t of a n e a r t h q u a k e. A c c o r d i n g l y, l a r g e s c a l e s h e a r t e s t s w e r e d o n e o n s t o n e c o l u m n s to d e m o n s t r a t e t h e i r a d e q u a c y ( E n g e l h a r d t a n d G o l d i n g, ). T h e r e s u l t s d e m o n s t r a t e d m o r e t h a n a d e q u a t e s h e a r r e s i s t a n c e. It s e e m s u n l i k e l y t h a t i n s u f f i c i e n t h o r i z o n t a l s h e a r i n g r e s i s t a n c e to s e i s m i c l o a d s c o u l d b e a p r o b l e m, b e c a u s e t h e c o e f f i c i e n t of f r i c t i o n of t h e c o l u m n w i l l i n v a r i a b l y b e g r e a t e r t h a n 0.7 (<j)s > 35 ) w h i c h w o u l d i m p l y a r e s i s t a n c e to s e i s m i c a l l y i n d u c e d g r o u n d a c c e l e r a t i o n s up to 0.7 g. E x p e r i e n c e s h o w s t h a t p o c k e t s o f loose, c o h e - s i o n l e s s s o i l s (fines c o n t e n t s < 20%) w i l l be d e n s i f i e d d u r i n g t h e i n s t a l l a t i o n o f s t o n e c o l u m n s b y v i b r a t o r y m e t h o d s. S a t u r a t e d, c o m p r e s s i b l e silts, h o w e v e r, p r o b a b l y w i l l not, a n d t h e s e m a t e r i a l s, as w e l l a s soft, s e n s i t i v e c l a y s, c o n c e i v a b l y c o u l d l o s e s t r e n g t h in a s t r o n g e a r t h q u a k e. T h e q u e s t i o n t h e n a r i s e s as t o w h e t h e r s u f f i c i e n t l a t e r a l c o n f i n e m e n t w i l l r e m a i n to s u p p o r t t h e c o l u m n. E v e n if t h e s o f t g r o u n d l o s e s a l l its s t r e n g t h, it w i l l s t i l l b e h a v e as a h i g h d e n s i t y fluid. P r o v i d e d the s t o n e c o l u m n is f u l l y d r a i n i n g to t h e g r o u n d s u r f a c e t h e w a t e r p r e s s u r e w i t h i n t h e c o l u m n w i l l b e h y d r o s t a t i c. T h e d i f f e r e n c e b e t w e e n t h i s p r e s s u r e a n d t h a t o f t h e h i g h d e n s i t y "f l u i d " s u r r o u n d i n g t h e c o l u m n, a u g m e n t e d by a n y a d d i t i o n a l s t r e s s a p p l i e d at t h e g r o u n d s u r f a c e, w i l l a c t as an e f f e c t i v e c o n f i n i n g p r e s s u r e. T h e v e r t i c a l s t r e s s t h a t c a n b e c a r r i e d b y t h e c o l u m n w o u l d t h e n b e t h i s s t r e s s t i m e s t a n 2 (45 + <(. /2). S t o n e c o l u m n f o u n d a t i o n s w e r e a d o p t e d f o r the s e w a g e t r e a t m e n t p l a n t. T h e c o m p l e t e d f a c i l i t y w a s s u b j e c t e d t o a m a g n i t u d e 5.1 e a r t h q u a k e w i t h l o c a l a c c e l e r a t i o n s u p to 0.3 g. N o d i s t r e s s r e l a t e d t o t h e f o u n d a t i o n s w a s o b s e r v e d. R o o t P i l e s T h e i n s t a l l a t i o n o f s m a l l d i a m e t e r ( mm) r o o t p i l e s r e q u i r e s d r i l l i n g a n d g r o u t i n g e q u i p m e n t. C a s e d b o r i n g s a r e m a d e u s i n g r o t a r y or p e r c u s s i o n m e t h o d s. R e i n f o r c e m e n t, u s u a l l y in t h e f o r m of a s i n g l e s t e e l bar, is p l a c e d in the c e n t e r of t h e c a s i n g. T h e h o l e is t h e n f i l l e d w i t h a h i g h slump, c e m e n t rich, s m a l l a g g r e g a t e c o n c r e t e. D u r i n g w i t h d r a w a l o f t h e c a s i n g a d d i t i o n a l c o n c r e t e is p l a c e d b y p u m p i n g o r a i r p r e s s u r e. T h e p r e s s u r e g u a r a n t e e s an i n t i m a t e c o n t a c t b e t w e e n c o n c r e t e a n d s o i l, f o r c e s p e n e t r a t i o n o f t h e c o n c r e t e i n t o c r a c k s a n d fissures, and, in t h e c a s e of c o m p r e s s i b l e s o i l s, p r o d u c e s a p i l e of l a r g e r d i a m e t e r t h a n t h e o r i g i n a l c a s i n g. I n d i v i d u a l r o o t p i l e s m a y h a v e b e a r i n g c a p a c i t i e s in the r a n g e o f 8 to 50 t ons. R o o t p i l e s c a n b e i n s t a l l e d in a l l t y p e s o f soil. F o r m a n y y e a r s s i n c e t h e i r i n t r o d u c t i o n o v e r 30 y e a r s ago, t h e u s e o f r o o t p i l e s w a s m a i n l y for u n d e r p i n n i n g a p p l i c a t i o n s, a t o p i c o u t s i d e t h e s c o p e o f t h i s r e p o r t. A c l u s t e r o f r o o t piles, u s u a l l y c o n t a i n i n g s o m e i n s t a l l e d a t a b a t t e r, c a n b e used, h o w e v e r, t o f o r m a s o r t o f i n - s i t u r e i n f o r c e d e a r t h m a s s. U s e d in t h i s w a y t h e s e " r e t i c u l a t e d r o o t p i l e " s t r u c t u r e s ( r e t i c u l a t e d P a l i Radice) h a v e a p p l i c a t i o n s to s l o p e s t a b i l i zation, r e t a i n i n g s t r u c t u r e s, a n d u n d e r g r o u n d c o n s t r u c t i o n. F i g u r e 44 is an e x a m p l e. Fig. 44 R e t i c u l a t e d R o o t P i l e R e t a i n i n g S t r u c t u r e for S l o p e S t a b i l i z a t i o n (Lizzi, 1977) W h i l e it is e v i d e n t t h a t t h e i n d i v i d u a l p i l e s w i t h i n a r e t i c u l a t e d r o o t p i l e s t r u c t u r e m a y be c a l l e d u p o n to c a r r y t e n s i o n, c o m p r e s s i o n, a n d f l e x u r a l s t r e s s e s, t h e i n t e r a c t i o n s w i t h t h e i n c l u d e d s o i l a r e c o m p l e x. If the p i l e s y s t e m w i t h t h e i n c l u d e d s o i l is t a k e n as a c o h e r e n t s t r u c t u r e, t h e n t h e t o t a l s y s t e m s t a b i l i t y c a n b e a n a l y z e d f o l l o w i n g u s u a l s o i l m e c h a n i c s p r o c e d u r e s. T h e i n t e r n a l d e s i g n ; i.e., t h e s e l e c t i o n o f p i l e size, a r r a n g e m e n t, a n d s p a c i n g, is m o s t l y b a s e d o n e x p e r i e n c e a n d f o l l o w s p a t e n t e d p r o c e d u r e s. F u r t h e r i n f o r m a t i o n o n r o o t p i l e s y s t e m s for g r o u n d i m p r o v e m e n t is g i v e n b y L i z z i (1977), S c h l o s s e r a n d J u r a n (1979), L i z z i a n d C a r n e v a l e (1979), a n d F l o s s (1979). T w o r e c e n t c a s e h i s t o r i e s a r e p r e s e n t e d b y D a s h a n d J o v i n o (1980) a n d M u r r a y (1980). S o i l N a i l i n g S o i l n a i l i n g, as s h o w n s c h e m a t i c a l l y in Fig. 41, is, in m a n y r e s p e c t s, s i m i l a r to r o o t p i l e s for g r o u n d s t r e n g t h e n i n g. T h i s is p e r h a p s m o r e e v i d e n t b y c o m p a r i s o n w i t h Fig. 45, w h i c h s h o w s a r o o t p i l e s y s t e m f o r s l o p e s t a b i l i z a t i o n. S o i l n a i l i n g is u s e d f o r g r o u n d s t r e n g t h e n i n g i n - s i t u, p r i m a r i l y f o r i m p r o v e m e n t o f s l o p e s t a b i l i t y a n d s u p p o r t o f e x c a v a t i o n s. T h e " n a i l s " a r e u s u a l l y s t e e l r o d s m m in d i a m e t e r t h a t a r e g r o u t e d i n t o p r e d r i l l e d h o l e s o r d r i v e n u s i n g a p e r c u s s i o n d r i l l i n g d e v i c e. T h e i r l e n g t h m a y be o f t h e o r d e r of 50 p e r c e n t o f t h e h e i g h t of t h e e x c a v a t i o n to b e s u p p o r t e d. T h e l e n g t h r e q u i r e d in t h e c a s e of the s t a b i l i z a t i o n of an e x i s t i n g s l o p e w i l l d e p e n d o n the l o c a t i o n o f t h e c r i t i c a l s h e a r p l a n e. T h e g r o u t e d b a r s c a n r e s i s t t e n s i l e f o r c e s t h a t a r e l i m i t e d b y t h e l e s s e r o f t h e b a r y i e l d s t r e n g t h a n d t h e p u l l - o u t r e s i s t a n c e p r o v i d e d b y t h e 547

40 Fig. 45 R o o t P i l e s U s e d for S l o p e S t a b i l i z a t i o n ( Lizzi, 1977) f r i c t i o n t h a t c a n b e m o b i l i z e d a l o n g t h e g r o u t - s o i l i n t e r f a c e. S h e a r a n d b e n d i n g s t r e s s e s w i l l b e d e v e l o p e d in t h e b a r s a t m a g n i t u d e s t h a t d e p e n d o n t h e s t i f f n e s s o f t h e b a r - g r o u t c o m b i n a t i o n r e l a t i v e to t h e soil. T h e a b i l i t y of t h e s o i l to r e s i s t l a t e r a l l o a d s a c t i n g t r a n s v e r s e l y to the n a i l a x i s m u s t a l s o be c o n s i d e r e d in t h e i n t e r n a l d e s i g n. T h e i n t e r n a l d e s i g n o f s o i l n a i l i n g s y s t e m s r e q u i r e s d e t e r m i n a t i o n o f t h e size, s p a c i n g, o r i e n t a t i o n, a n d l e n g t h o f b a r s. O v e r a l l s t a b i l i t y of t h e n a i l e d s o i l m a s s c a n be a n a l y z e d in the u s u a l way. R e c e n t w o r k o n s o i l n a i l i n g h a s b e e n s u m m a r i z e d b y S c h l o s s e r a n d J u r a n (1979), a n d r e s e a r c h o n the s u b j e c t is c o n t i n u i n g. T h e e a r t h s u p p o r t s y s t e m d e s c r i b e d b y B a n g e t a l. (1980) a n d i l l u s t r a t e d in Fig. 46 h a s c h a r a c t e r i s t i c s b o t h of s o i l n a i l i n g a n d a r e i n f o r c e d e a r t h w a l l c o n s t r u c t e d i n - s i t u. T h e s y s t e m is c o m p o s e d o f a 0. 1 m - t h i c k w i r e m e s h - r e i n f o r c e d s h o t c r e t e f a c i n g, r e i n f o r c e m e n t s s p a c e d f r o m 0.9 t o 1.8 m a p a r t t h a t a r e g r o u t e d i n t o t h e soil, a n d r o w s o f r e i n f o r c i n g b a r s t h a t f o r m h o r i z o n t a l w a l e s at e a c h a n c h o r level. L e v e l s of r e i n f o r c e m e n t a r e p l a c e d i m m e d i a t e l y a f t e r e a c h s t a g e o f e x c a v a t i o n. T e n s i l e R e i n f o r c e m e n t s I n c l u s i o n s o f t e n s i l e r e i n f o r c e m e n t s in s o i l s m a y b e o f t w o b a s i c types: i d e a l l y i n e x t e n s i b l e m a t e r i a l s, s u c h as m e t a l s t r i p s a n d b a r s, a n d i d e a l l y e x t e n s i b l e m a t e r i a l s s u c h as f i bers, r o o t s a n d g e o t e x t i l e s. T h e f i r s t t y p e is c h a r a c t e r i s t i c o f s y s t e m s u s e d to c o n s t r u c t r e i n f o r c e d e a r t h s t r u c t u r e s. T h e s e c o n d h a s b e e n t e r m e d " p l y - s o i l " b y M c G o w n e t al. (1978). T h e c h a r a c t e r i s t i c s o f t h e s e t w o t y p e s o f r e i n f o r c e d s y s t e m s a r e c o m p a r e d in T a b l e XI. T h e c h o i c e in a n y c a s e is l i k e l y to b e c o n t r o l l e d b y a l l o w a b l e d e f o r m a t i o n s. R e i n f o r c e d E a r t h R e i n f o r c e d e a r t h is a c o m p o s i t e c o n s t r u c t i o n m a t e r i a l t h a t is m a d e i n t e r n a l l y s t a b l e b y t h e Fig. 46 C r o s s S e c t i o n o f R e i n f o r c e d G r o u n d S y s t e m for D e e p E x c a v a t i o n s ( Bang e t al., 1980) i n t e r a c t i o n b e t w e e n soil, w h i c h, f o r c e r t a i n g r a d a t i o n s a n d c o m p a c t i o n c o n d i t i o n s, is s t r o n g i n c o m p r e s s i o n a n d shear, a n d r e i n f o r c e m e n t s, w h i c h a r e s t r o n g in t e n s i o n. W h i l e t h e s t r e n g t h e n i n g e f f e c t s o f l i n e a r t e n s i l e r e i n f o r c i n g e l e m e n t s in s o i l s h a v e b e e n r e c o g n i z e d a n d u t i l i z e d f o r c e n t u r i e s, it h a s b e e n o n l y in t h e l a s t 15 y e a r s t h a t l a r g e - s c a l e r e i n f o r c e d e a r t h c o n s t r u c t i o n h a s b e e n u n d e r t a k e n, a n d t h e m e c h a n i s m s u n d e r l y i n g r e i n f o r c e d e a r t h b e h a v i o r h a v e b e e n e l u c i d a t e d. M u c h o f t h e c u r r e n t d e v e l o p m e n t c a n b e a t t r i b u t e d to t h e p i o n e e r i n g w o r k o f V i d a l (1966). E a r t h r e i n f o r c e d w i t h h i g h m o d u l u s l i n e a r tensile e l e m e n t s m a y be an e c o n o m i c a l c o n s t r u c t i o n m a t e r i a l for a v a r i e t y of a p p l i c a t i o n s, i n c l u d i n g r e t a i n i n g w a l l s, b r i d g e a b u t m e n t s, e m b a n k m e n t s, t h e b r i d g i n g o f c a v e r n s i n l i m e s t o n e, c o n t a i n m e n t d i k e s, c o a l a n d o r e s t o r a g e s l o t s w i t h s l o p i n g faces, a n d h o u s i n g o n s l o p i n g t e r r a i n. T h e r e m a y b e a p p l i c a t i o n in a n y s i t u a t i o n w h e r e a s t a b l e c h a n g e in e l e v a t i o n u p to 30 to 40 m is r e q u i r e d a n d s u i t a b l e s o i l b a c k f i l l is a v a i l a b l e. A t y p i c a l r e i n f o r c e d e a r t h w a l l o f t h e V i d a l type is s h o w n in Fig. 47. S u c h s t r u c t u r e s, if p r o p e r l y d e s i g n e d, b e h a v e as c o h e r e n t, s e l f - c o n t a i n e d u n i t s ( M c K i t t r i c k, 1979). R e i n f o r c e d e a r t h s t r u c t u r e s p o s s e s s f l e x i b i l i t y a n d c a n t o l e r a t e s o m e d e f o r m a t i o n w i t h o u t d i s t r e s s. A s a r e s u l t t h e y c a n b e u s e d in s i t u a t i o n s w h e r e s o m e g r o u n d m o v e m e n t s a r e a n t i c i p a t e d, a n d in c o m b i n a t i o n w i t h o t h e r f o r m s of g r o u n d i m p r o v e m e n t. A n e x a m p l e is s h o w n in Fig. 48. B e c a u s e 548

41 TABLE XI C o m p a r a t i v e B e h a v i o r o f E a r t h R e i n f o r c e m e n t T y p e o f R e i n f o r c e m e n t S t r e s s - D e f o r m a t i o n B e h a v i o r o f R e i n f o r c e m e n t R o l e a n d F u n c t i o n o f R e i n f o r c e m e n t I d e a l l y i n e x t e n s i b l e i n c l u s i o n s (metal a n d p l a s t i c s t r i p s, b a r s, g r i d s, etc.) I d e a l l y e x t e n s i b l e i n c l u s i o n s ( n a t u r a l a n d s y n t h e t i c f i b e r s, r o o t s, f a b r i c s, g e o t e x t i l e s ) I n c l u s i o n s h a v e r u p t u r e s t r a i n s l e s s t h a n t h e m a x i m u m t e n s i l e s t r a i n s in t h e soil w / o i n c l u s i o n s, u n d e r t h e s a m e s t r e s s c o n d i t i o n s, i.e., (er> r u p < e s r m a x D e p e n d i n g o n t h e u l t i m a t e s t r e n g t h o f t h e i n c l u s i o n s in r e l a t i o n to t h e i m p o s e d loads, t h e s e i n c l u s i o n s m a y o r m a y n o t r u p t u r e. I n c l u s i o n s h a v e r u p t u r e s t r a i n s l a r g e r t h a n the m a x i m u m t e n s i l e s t r a i n s in t h e soil w / o i n c l u s i o n s, i.e., (er> r u p > Es r m a x T h e s e i n c l u s i o n s c a n n o t r u p t u r e n o m a t t e r t h e i r u l t i m a t e s t r e n g t h n o r t h e i m p o s e d load. S t r e n g t h e n s s o i l ( i n c r e a s e s a p p a r e n t s h e a r r e s i s t a n c e ) a n d i n h i b i t s b o t h i n t e r n a l a n d b o u n d a r y d e f o r m a t i o n s. C a t a s t r o p h i c f a i l u r e a n d c o l l a p s e of s o i l c a n o c c u r if r e i n f o r c e m e n t b r e a k s. S o m e s t r e n g t h e n i n g... b u t m o r e i m p o r t a n t l y p r o v i d e s g r e a t e r e x t e n s i b i l i t y (ductility) a n d s m a l l e r loss o f p o s t p e a k s t r e n g t h c o m p a r e d to s o i l alone. ( a d a p t e d f r o m D.H. G r a y, l e c t u r e, U n i v e r s i t y o f C a l i f o r n i a, B e r k e l e y, F e b r u a r y 26, 1981) E a r t h r e i n f o r c e m e n t h a s b e e n e x t e n s i v e l y s t u d i e d i n r e c e n t y e a r s, a n d to p r o v i d e a c o m p r e h e n s i v e r e v i e w o f a l l a s p e c t s in t h i s r e p o r t is n o t p o s s i b l e. C o n s e q u e n t l y, a t t e n t i o n h e r e i n is d i r e c t e d p r i m a r i l y at t h e c o n c e p t a n d e s s e n t i a l f e a t u r e s o f r e i n f o r c e d e a r t h a n d t h e p r i n c i p l e s u n d e r l y i n g the d e s i g n of r e i n f o r c e d e a r t h s t r u c t u r e s. R e c e n t p u b l i c a t i o n s t h a t p r e s e n t d e t a i l e d i n f o r m a t i o n o n e a r t h r e i n f o r c e m e n t w i t h t e n s i l e e l e m e n t s i n c l u d e A S C E (1978), C o m m i t t e e o n P l a c e m e n t a n d I m p r o v e m e n t o f S o i l s (1978), N e w S o u t h W a l e s (1978), E N P C - L C P C (1979), M c K i t t r i c k (1979), a n d S c h l o s s e r a n d J u r a n (1979). Fig. 47 T y p i c a l R e i n f o r c e d E a r t h W a l l o f r i g h t o f w a y l i m i t a t i o n s a h i g h w a y a l i g n m e n t w a s r e q u i r e d a t t h e l o c a t i o n s h o w n in Fig. 48a a l o n g t h e s h o r e l i n e o f L a k e P e n d O r e i l l e in Utah, U. S. A. T h e c o n v e n t i o n a l e m b a n k m e n t s o l u t i o n w o u l d h a v e b e e n d i f f i c u l t b e c a u s e o f the l a r g e q u a n t i t i e s o f m a t e r i a l r e q u i r e d a n d t h e l o w s t r e n g t h o f the l o o s e s a n d y s ilt. I n s t e a d t h e s o l u t i o n s h o w n in Fig. 48 w a s a d o p t e d w h i c h c o n s i s t s o f a r e i n f o r c e d e a r t h s u p p o r t e d e m b a n k m e n t f o u n d e d o n v i b r o - r e p l a c e m e n t s t o n e c o l u m n s. T h r e e e l e m e n t s c o m p r i s e a r e i n f o r c e d e a r t h w a l l s y s t e m : f a c i n g, r e i n f o r c e m e n t s, a n d b a c k f i l l s oil, as s h o w n s c h e m a t i c a l l y in Fig. 49. T h e r e i n f o r c i n g s t r i p l e n g t h s a r e u s u a l l y a b o u t 0.7 to 0.8 t i m e s t h e h e i g h t o f t h e w a l l. D i f f e r e n t a r r a n g e m e n t s a n d t y p e s of f a c i n g s a n d r e i n f o r c e m e n t s h a v e b e e n d e v e l o p e d. F o r e x a m p l e, in the t y p i c a l V i d a l - t y p e o f w a l l c o n c r e t e f a c i n g p a n e l s a n d g a l v a n i z e d r i b b e d s t e e l r e i n f o r c i n g s t r i p s 5 x 40 m m o r 5 x 60 m m in c r o s s s e c t i o n a r e p r e s e n t l y u s e d. W i r e m e s h, f a bric, a n d g a l v a n i z e d s h e e t or c o r r u g a t e d f a c i n g s a r e u s e d by s o m e m a n u f a c t u r e r s, as a r e b a r grid, w i r e m e s h, p l a s t i c, f i b e r g l a s s a n d g e o t e x t i l e r e i n f o r c e m e n t s. F u k u o k a (1980) d e s c r i b e s a r e t a i n i n g s t r u c t u r e w i t h o i l b a r r e l h a l v e s u s e d for t h e facing. O f p r i m a r y c o n s i d e r a t i o n in the s e l e c t i o n of t h e r e i n f o r c e m e n t s a r e t h e i r s t r e n g t h, m o d u l u s, a n d d u r a b i l i t y. T h e f a c i n g 549

42 Rein force ment Reinforced earth wchi I Platform High pool El '.3058' ljqw pool El ' < ^ in a l riprap slope :Stone ^ v r j ( p t ectjon columns ^ < N Reinforcement thickness = t Bed roc k Fig. 49 R e i n f o r c e d E a r t h W a l l S y s t e m Fig. 48 b. R e i n f o r c e d E a r t h W a l l S u p p o r t e d b y S t o n e C o l u m n s C o m b i n a t i o n o f R e i n f o r c e m e n t S y s t e m s p a n e l s a r e r e q u i r e d to c a r r y l o c a l s t r e s s c o n c e n t r a t i o n s f r o m t h e s o i l in z o n e s s o m e d i s t a n c e f r o m t h e r e i n f o r c e m e n t s. In a d d i t i o n, t h e p a n e l s a n d t h e c o n n e c t i o n s to t h e r e i n f o r c e m e n t s m u s t r e s i s t s t r e s s e s i n d u c e d b y c o n s t r u c t i o n e q u i p m e n t a n d b a c k f i l l c o m p a c t i o n c l o s e to t h e w a l l. T h e k e y to t h e s t a b i l i t y o f a r e i n f o r c e d e a r t h s t r u c t u r e is the i n t e r a c t i o n b e t w e e n t h e s o i l a n d r e i n f o r c e m e n t s. A p r o p e r l y d e s i g n e d a n d c o n s t r u c t e d s t r u c t u r e h o l d s i t s e l f t o g e t h e r as a c o h e r e n t b o d y b e c a u s e o f t h i s i n t e r a c t i o n, w h i c h p r e v e n t s t h e s o i l f r o m s p r e a d i n g l a t e r a l l y in t h e d i r e c t i o n o f t h e r e i n f o r c e m e n t s. A n e f f e c t i v e c o n f i n e m e n t o r a p p a r e n t c o h e s i o n is d e v e l o p e d in the s o i l o w i n g to t h e t e n s i l e s t i f f n e s s o f t h e r e i n f o r c e m e n t s w h i c h r e s t r a i n t h e s oil. L i n e a r t e n s i l e r e i n f o r c e m e n t s e x e r t t h e i r g r e a t e s t s t r e n g t h e n i n g e f f e c t w h e n o r i e n t e d in t h e d i r e c t i o n of p r i n c i p a l s t r a i n e x t e n sion, as s h o w n b y r e c e n t a n a l y s e s s u c h as t h o s e b y B a s s e t t a n d L a s t (1978) a n d J e w e l l (1980). C o m p r e h e n s i v e r e v i e w s of t h e e a r t h r e i n f o r c e m e n t m e c h a n i s m a r e p r e s e n t e d b y M i t c h e l l a n d S c h l o s s e r (1979) a n d M c K i t t r i c k (1979). A s t h e r e s i s t a n c e m o b i l i z e d b e t w e e n t h e soil a n d t e n s i l e r e i n f o r c e m e n t s is p r o b a b l y t h e m o s t i m p o r t a n t a s p e c t o f r e i n f o r c e d e a r t h, q u e s t i o n s r e l a t i n g to h o w i t is d e v e l o p e d, h o w it v a r i e s a l o n g t h e r e i n f o r c e m e n t s, h o w to m e a s u r e it, a n d h o w to e x p r e s s it in d e s i g n a r e o f g r e a t i n t e r e s t. T h e m e a s u r e m e n t o f t h e a p p a r e n t f r i c t i o n c o e f f i c i e n t, f*, b e t w e e n s o i l a n d r e i n f o r c e m e n t s h a s b e e n d o n e u s i n g s e v e r a l t e s t t y p e s as s h o w n s c h e m a t i c a l l y in Fig. 50. P u l l - o u t t e s t s h a v e b e e n d o n e b o t h o n m o d e l s a n d full s c a l e w a l l s. S o m e r e i n f o r c i n g m a t e r i a l s s u c h as f a b r i c s, n e t s, a n d m e s h e s, m a y h a v e s t r e s s - s t r a i n p r o p e r t i e s t h a t d e p e n d o n t h e l a t e r a l c o n f i n i n g s t r e s s a p p l i e d to them. A n a p p a r a t u s s u i t a b l e f o r d e t e r m i n i n g t h e s e p r o p e r t i e s is d e s c r i b e d b y A n d r a w e s e t al. (1980). A l t h o u g h t h e p u l l o u t t e s t is o f t e n c o n s i d e r e d t h e m o s t a p p r o p r i a t e, t h e s t r e s s d i s t r i b u t i o n s a l o n g t h e r e i n f o r c e m e n t s d o n o t d u p l i c a t e e x a c t l y t h o s e in an a c t u a l w a l l, as m a y be s e e n f r o m Fig. 51. T h e v a l u e of f* h a s b e e n s h o w n (e.g., M c K i t t r i c k, 1979) to v a r y w i t h t y p e o f r e i n f o r c e m e n t, t y p e o f b a c k f i l l, d e n s i t y o f b a c k f i l l, a n d c o n f i n i n g p r e s s u r e. T h e i n f l u e n c e o f o v e r b u r d e n p r e s s u r e o n f* for s m o o t h a n d r i b b e d s t r i p r e i n f o r c e m e n t s is s h o w n in Fig. 52. R e i n f o r c e m e n t s w i t h ribs, d e f o r m a t i o n s, o r o t h e r w i s e r o u g h s u r f a c e s g i v e h i g h e r v a l u e s t h a n r e i n f o r c e m e n t s w i t h s m o o t h s u r f a c e s, b e c a u s e s o i l - t o - s o i l p r o p e r ti e s c o n t r o l b e h a v i o r r a t h e r t h a n s o i l - t o - 550

43 Grovel.. Soil. *. 7S/2?/s;/;/2222;/A Reinforcing moteriol T Ribbed /= 21 kn/m3 4> - 46 internol friction ^ = 27.5 soil-strip friction f * T / N D ire c t Shear Test f* = t / n PULL O UT TE S T IN SHEAR BOX ton <t> tan Height of Fill Above Strip, H -m f = C7V x area P U L L O U T T E S T O N W A L L Fig. 52 E f f e c t o f O v e r b u r d e n P r e s s u r e o n the A p p a r e n t C o e f f i c i e n t o f F r i c t i o n f* PU LL O UT TE S T BY ROTATION ( Alimi et al., 1977) F i g. 50 Case Shear Stress Tie Tension T y p e s o f T e s t f o r M e a s u r e m e n t of S o i l - R e i n f o r c e m e n t F r i c t i o n Ideal Pull-Out Test Ideal Reinforcing Reinforced Earth Retaining Wall B a c k f i l l m a t e r i a l s for p e r m a n e n t r e i n f o r c e d e a r t h s t r u c t u r e s a r e u s u a l l y l i m i t e d to g r a n u l a r soils. O n e c u r r e n t s p e c i f i c a t i o n r e q u i r e s t h a t t h e p l a s t i c i t y i n d e x b e less t h a n 6 p e r c e n t, t h e f r i c t i o n a n g l e b e g r e a t e r t h a n 34, a n d t h a t t h e r e b e l e s s t h a n 15 p e r c e n t b y w e i g h t f i n e r t h a n 15 pm. T h e s u i t a b i l i t y o f c o h e s i v e s o i l s is l i m i t e d for t h e f o l l o w i n g r e a s o n s : 1. T h e f r i c t i o n a l s t r e n g t h, a t l e a s t u n d e r the u n d r a i n e d c o n d i t i o n s r e l e v a n t to s t a b i l i t y i m m e d i a t e l y a f t e r c o n s t r u c t i o n, is low. 2. C o h e s i v e b a c k f i l l s a r e l i k e l y to b e p o o r l y d r a i n i n g a n d s u s c e p t i b l e to s t r e n g t h l o s s o n w e t t i n g. 3. S i g n i f i c a n t c o n t i n u i n g c r e e p d e f o r m a t i o n s m a y o c c u r u n d e r t h e s u s t a i n e d s t r e s s e s t h a t t h e b a c k f i l l is c a l l e d u p o n to r e s i s t. 4. C o h e s i v e s o i l s a r e u s u a l l y d i f f i c u l t to c o m p a c t. Fig. 51 Tmax - Max. Tie Tension Ft - Tie Force at Wall Face 6 - Equivalent Skin Friction Angle e (Computed from T,) <<Sn H y p o t h e t i c a l S h e a r S t r e s s D i s t r i b u t i o n s A l o n g R e i n f o r c e m e n t s ( H a u s m a n a n d Lee, 19 78) r e i n f o r c e m e n t v a l u e s. T h e v a l u e o f f* d e c r e a s e s w i t h i n c r e a s i n g o v e r b u r d e n p r e s s u r e p r i m a r i l y b e c a u s e t h e i n c r e a s e d p r e s s u r e s u p p r e s s e s d i l a - t a n c y. A s d i l a t a n c y is e s s e n t i a l l y r e s p o n s i b l e f o r t h e h i g h v a l u e o f f*, i t s s u p p r e s s i o n l e a d s to v a l u e s c l o s e to t a m p a n d tan<t> for s m o o t h a n d r i b b e d s t r i p s, r e s p e c t i v e l y, as s h o w n in Fig. 52. B o t h t h e o v e r a l l s t a b i l i t y o f a r e i n f o r c e d e a r t h s t r u c t u r e in r e l a t i o n to t h e s i t e o n w h i c h it is u s e d a n d t h e i n t e r n a l s t a b i l i t y o f the r e i n f o r c e d v o l u m e o f s o i l m u s t b e e v a l u a t e d for d e s i g n. T h e o v e r a l l s t a b i l i t y i n c l u d e s c o n s i d e r a t i o n s o f s l i d i n g, o v e r t u r n i n g, f o u n d a t i o n b e a r i n g c a p a c i t y, a n d s l o p e s t a b i l i t y, a n d c o n v e n t i o n a l p r o c e d u r e s o f a n a l y s i s c a n be u sed. E s s e n t i a l c o n s i d e r a t i o n s for i n t e r n a l s t a b i l i t y a r e t h a t t h e r e i n f o r c e m e n t s be s a f e a g a i n s t b o t h p u l l o u t a n d r u p t u r e. It is p r e f e r a b l e to d e s i g n so t h a t if a n y f a i l u r e s in t h e r e i n f o r c e m e n t o c c u r t h e y w i l l b e b y p u l l o u t r a t h e r t h a n by r u p t u r e in o r d e r to m i n i m i z e t h e r i s k o f c a t a s t r o p h i c f a i l u r e o f t h e s t r u c t u r e s h o u l d the r e i n f o r c e m e n t s f a i l b y a p r o g r e s s i v e m e c h a n i s m. T h e r e s u l t s o f b o t h m o d e l a n d f i e l d t e s t s on i n s t r u m e n t e d s t r u c t u r e s, as w e l l as a n a l y s e s b y v a r i o u s m e t h o d s, h a v e e s t a b l i s h e d t h a t t h e l o c u s o f m a x i m u m t e n s i l e f o r c e s in t h e r e i n f o r c e m e n t s d e f i n e s a c t i v e a n d r e s i s t a n t z o n e s w i t h i n the 551

44 v o l u m e o f r e i n f o r c e d e a r t h. T h e loci o f m a x i m u m t e n s i l e f o r c e s a n d t h e d i s t r i b u t i o n o f t e n s i l e f o r c e s a l o n g the r e i n f o r c e m e n t s a r e s h o w n for f o u r t y p e s o f r e i n f o r c e d e a r t h s t r u c t u r e in Fig. 53. b) R e ta in in g Wall Fig. 54 D e s i g n G e o m e t r y for a S i m p l e R e i n f o r c e d E a r t h W a l l 2b f* 1 a ' c) V a u lt d ) B rid g e Abutm ent ^ > 1.5 (49) Fig. 5 3 L o c u s o f M a x i m u m T e n s i l e F o r c e s in D i f f e r e n t R e i n f o r c e d E a r t h S t r u c t u r e s T h e i n t e r n a l d e s i g n o f a s i m p l e r e i n f o r c e d e a r t h w a l l is i l l u s t r a t i v e. T h e a c t i v e a n d r e s i s t a n t z o n e s c a n b e a p p r o x i m a t e d b y t h e g e o m e t r y in F ig. 54. M e a s u r e m e n t s j u s t i f y t h e u s e o f f* = 1.2 at t h e g r o u n d s u r f a c e, d e c r e a s i n g l i n e a r l y to tan<)> a t a d e p t h o f 6 m a n d c o n s t a n t a t tan<(i b e l o w for r i b b e d r e i n f o r c e m e n t s, a n d t h e u s e o f f* = 0.4 f o r s m o o t h r e i n f o r c e m e n t s. M e a s u r e m e n t s h a v e a l s o e s t a b l i s h e d t h a t t h e h o r i z o n t a l s t r e s s a h to b e c a r r i e d b y t h e r e s i s t a n t z o n e at a n y d e p t h c a n b e d e f i n e d by a, = a K (47) h v w h e r e a y is t h e v e r t i c a l s t r e s s, a n d K is an e a r t h p r e s s u r e c o e f f i c i e n t. K c a n be t a k e n as K q a t t h e g r o u n d s u r f a c e, d e c r e a s i n g l i n e a r l y t o K a a t a d e p t h o f 6 m a n d b e l o w, w h e r e K = 1 - sinij) (48) K a = t a n 2 (45 - Q/2) T h e e f f e c t i v e l e n g t h o f r e i n f o r c e m e n t s, le, is t h e l e n g t h to t h e r i g h t o f t h e a c t i v e z o n e in Fig. 54. A f a c t o r o f s a f e t y o f at l e a s t 1.5 a g a i n s t s t r i p p u l l o u t is u s u a l l y r e q u i r e d, a n d t h e m a x i m u m t e n s i l e s t r e s s in the r e i n f o r c e m e n t m u s t b e l e s s t h a n t h e a l l o w a b l e f o r t h e m a t e r i a l. F o r t h e s t r i p p u l l o u t c o n d i t i o n i n w h i c h b is t h e s t r i p w i d t h, a v ' = yh, y is the e f f e c t i v e u n i t w e i g h t o f t h e b a c k f i l l, h is t h e d e p t h to t h e s t r i p in q u e s t i o n, S is the h o r i z o n t a l s p a c i n g o f r e i n f o r c e m e n t s, a n d V is t h e i r v e r t i c a l s p a c i n g. T h e m a x i m u m t e n s i l e s t r e s s, f t, in t h e r e i n f o r c e m e n t c a n b e f o u n d f r o m w h e r e A s is t h e c r o s s - s e c t i o n a l a r e a of r e i n f o r c e m e n t. If m e t a l l i c r e i n f o r c e m e n t s a r e u s e d, t h e r e m u s t be a n a l l o w a n c e for c o r r o s i o n t h a t w i l l o c c u r o v e r t h e l i f e o f t h e s t r u c t u r e. T h e d u r a b i l i t y o f m e t a l l i c r e i n f o r c e m e n t s is d i s c u s s e d b y K i n g (1977) a n d M c K i t t r i c k (1979). If s y n t h e t i c m a t e r i a l s a r e used, t h e n it is n e c e s s a r y to c o n s i d e r s u c h f a c t o r s as t h e i r c r e e p p r o p e r t i e s a n d t h e i r l o n g - t e r m c h e m i c a l a n d b i o l o g i c a l s t a b i l i t y. R e i n f o r c e d e a r t h s t r u c t u r e s h a v e b e e n u s e d s u c c e s s f u l l y i n s e i s m i c a r e a s, a n d t h e r e h a v e b e e n n o r e c o r d e d f a i l u r e s as a r e s u l t o f e a r t h q u a k e s. T h e r e s u l t s o f m o d e l t e s t s a n d l i m i t e d f i e l d t e s t s w e r e u s e d b y R i c h a r d s o n a n d L e e (1975) a n d R i c h a r d s o n (1978) to p r o p o s e m e t h o d s f o r the s e i s m i c d e s i g n o f r e i n f o r c e d e a r t h w a l l s. T h e m o s t s i g n i f i c a n t c o n s e q u e n c e s o f s e i s m i c l o a d i n g s a p p e a r to b e t h a t a s o m e w h a t i n c r e a s e d w i d t h of r e i n f o r c e d z o n e is r e q u i r e d to i n s u r e o v e r a l l s t a b i l i t y o f t h e s t r u c t u r e, a n d a d d i t i o n a l r e i n f o r c e m e n t is r e q u i r e d at s h a l l o w d e p t h s to 552

45 i n s u r e i n t e r n a l s t a b i l i t y. F u r t h e r s t u d y of t h e s e i s m i c b e h a v i o r of r e i n f o r c e d e a r t h is in p r o g r e s s. G e o t e x t i l e s in E a r t h R e i n f o r c e m e n t T h e r a p i d e m e r g e n c e a n d u t i l i z a t i o n of s y n t h e t i c f a b r i c s in g e o t e c h n i c a l a p p l i c a t i o n s h a s b e e n o n e o f t h e m a j o r d e v e l o p m e n t s of t h e p a s t 10 y e a r s. A v e r y l a r g e n u m b e r o f m a t e r i a l s e n c o m p a s s i n g a w i d e r a n g e of p r o p e r t i e s h a s b e e n d e v e l o p e d f o r s p e c i a l p u r p o s e s. B e c a u s e c o n s t r u c t i o n f a b r i c s h a v e a s s u m e d s u c h an i m p o r t a n t r o l e in t h e g e o t e c h n i c a l f i e l d t h e y w e r e g i v e n t h e n a m e " g e o t e x t i l e s " b y J. P. G i r o u d a t the E N P C - L C P C I n t e r n a t i o n a l C o n f e r e n c e o n t h e u s e of F a b r i c s in G e o t e c h n i c s h e l d in P a r i s in 1977 ( E N P C - L C P C, 1977). A b o o k d e v o t e d s o l e l y to c o n s t r u c t i o n a n d g e o t e c h n i c a l e n g i n e e r i n g u s e s o f s y n t h e t i c f a b r i c s h a s r e c e n t l y a p p e a r e d ( K o e r n e r a n d W e l s h, 1980). G e o t e x t i l e s c a n s e r v e s e v e r a l f u n c t i o n s, i n c l u d i n g s e p a r a t i o n, r e i n f o r c e m e n t, d r a i n a g e, e r o s i o n c o n t r o l, forms, a n d i m p e r m e a b l e m e m b r a n e s. T h e m o s t i m p o r t a n t o f t h e s e r e l a t i v e t o g r o u n d i m p r o v e m e n t a r e d r a i n a g e a n d r e i n f o r c e m e n t. A l t h o u g h n o t d e a l t w i t h in d e t a i l in t h i s r e p o r t, m o i s t u r e c o n t e n t c o n t r o l b y p r o p e r d r a i n a g e m e a s u r e s c a n be o n e o f t h e m o s t e f f e c t i v e m e a n s f o r s o i l s t a b i l i z a t i o n. G e o t e x t i l e s c a n b e u s e d e c o n o m i c a l l y in m a n y d r a i n a g e s i t u a t i o n s as d e s c r i b e d b y K o e r n e r a n d W e l s h (1980). Fig. 55 T y p ic a l overlap in. h H T y p i c a l C r o s s S e c t i o n o f F a b r i c R e t a i n i n g W a l l ( K o e r n e r a n d W e l s h, 1980) P r e s e n t l y a v a i l a b l e g e o t e x t i l e s a c t as e x t e n s i b l e i n c l u s i o n s. T a b l e XI. O n e o f t h e i r m o s t i m p o r t a n t u s e s h a s b e e n f o r t h e c o n s t r u c t i o n of t e m p o r a r y r o a d s o v e r m a r s h e s, p e a t s o i l s, a n d c o m p r e s s i b l e c l a y s. A l a y e r of f a b r i c b e t w e e n t h e s u r f a c e of t h e s o f t g r o u n d a n d a g r a v e l b a s e s e r v e s b o t h t o s e p a r a t e t h e m a t e r i a l s a n d p r e v e n t t h e i r m i x i n g a n d t o s p r e a d v e r t i c a l v e h i c l e l o a d s o v e r t h e f o u n d a t i o n, t h u s r e d u c i n g t h e i n d u c e d s h e a r s t r e s s e s. T h e d e t a i l e d m e c h a n i s m s i n a l l c a s e s h a v e n o t b e e n f u l l y e l u c i d a t e d. A m a j o r factor, h o w e v e r, is t h a t t h e f a b r i c w h e n d e f o r m e d u n d e r t h e a p p l i e d l o a d s b e c o m e s s t r e s s e d in t e n s i o n. T h i s, in t urn, r e a c t s a l o n g t h e b o t t o m o f t h e o v e r l y i n g g r a v e l layer, i n c r e a s i n g its e f f e c t i v e c o n f i n e m e n t and, t h e r e f o r e, its s t i f f n ess. T h e u s e f u l n e s s of f a b r i c s in t h i s a p p l i c a t i o n i n c r e a s e s m a r k e d l y as s u b g r a d e s t r e n g t h d e c r e a s e s, w i t h t h e i r g r e a t e s t a p p l i c a t i o n to s o i l s o f C B R ( C a l i f o r n i a B e a r i n g Ratio) less t h a n 3. D e s i g n m e t h o d s a r e p r e s e n t e d b y K o e r n e r a n d W e l s h (1980). S i m i l a r m e c h a n i s m s a n d d e s i g n c o n s i d e r a t i o n s a p p l y f o r g e o t e x t i l e s u s e d f o r s u p p o r t o f e m b a n k m e n t s o v e r s o f t s o i l s o r to i m p r o v e t h e b e a r i n g c a p a c i t y o f s h a l l o w f o u n d a t i o n s. In t h e s e l a t t e r a p p l i c a t i o n s e m b e d m e n t l e n g t h o r a n c h o r d e s i g n to i n s u r e a g a i n s t f a b r i c p u l l o u t m a y be c r i t i c a l. G e o t e x t i l e s c a n b e u s e d in t h e c o n s t r u c t i o n of r e i n f o r c e d e a r t h w a l l s. F a b r i c w a l l s m a y b e e s p e c i a l l y w e l l s u i t e d a n d e c o n o m i c a l f o r r e l a t i v e l y l o w w a l l s in r u r a l or f o r e s t a r e a s. A t y p i c a l c r o s s s e c t i o n for a f a b r i c r e t a i n i n g wall is s h o w n in Fig. 55. W h e n e x p o s e d f a b r i c is used, p r e c a u t i o n s a g a i n s t t h e d e t e r i o r a t i n g e f f e c t s of u l t r a v i o l e t l i g h t a n d v a n d a l i s m a r e r e q u i r e d. U s e o f f a b r i c s in a s m a l l e a r t h d a m h a s a l s o b e e n m a d e, as i l l u s t r a t e d in Fig. 56. T h e f a b r i c u s e d in t h i s c a s e w a s a w o v e n p o l y e s t e r f i l l e d w i t h a l o a m soil. F i g. 56 F a b r i c E a r t h D a m (Kern, 1977) F i n a l l y, f a b r i c c o n t a i n m e n t s y s t e m s, in w h i c h s o i l is c o m p l e t e l y e n v e l o p e d b y t h e g e o t e x t i l e, c a n b e u s e f u l. In t h i s c a s e t h e t e n s i l e strength o f t h e f a b r i c r e s t r a i n s t h e e n c a p s u l a t e d soil. If i m p e r v i o u s f a b r i c is u s e d, t h e e n c l o s e d soil c a n b e p r o t e c t e d a g a i n s t d e t r i m e n t a l m o i s t u r e c o n t e n t c h a n g e s. M E S L ( M e m b r a n e E n c a p s u l a t e d S o i l Layer) c o n s t r u c t i o n h a s b e e n u s e d for r o a d a n d a i r f i e l d c o n s t r u c t i o n. E n c a p s u l a t e d d i k e a n d e m b a n k m e n t s t r u c t u r e s m a y b e s u i t a b l e for s o m e a p p l i c a t i o n s. C O M P A R I S O N A N D S E L E C T I O N O F M E T H O D S T h e e s s e n t i a l a s p e c t s o f a l a r g e n u m b e r o f soil i m p r o v e m e n t m e t h o d s h a v e b e e n p r e s e n t e d in t h e p r e c e d i n g p a g e s. T h e s e l e c t i o n of t h e m o s t s u i t a b l e o n e in a n y c a s e c a n o n l y b e m a d e a f t e r e v a l u a t i o n o f s e v e r a l f a c t o r s s p e c i f i c to the p r o b l e m a t h a n d. M o s t i m p o r t a n t a m o n g t h e s e are: 1. T h e p u r p o s e to w h i c h t h e t r e a t e d g r o u n d w i l l b e put. T h i s w i l l e s t a b l i s h t h e l e v e l o f i m p r o v e m e n t r e q u i r e d in t e r m s of p r o p e r t i e s s u c h as s t r e n g t h, s t i f f n e s s, c o m p r e s s i b i l i t y, a n d p e r m e a b i l i t y. 553

46 2. T h e a rea, d e p t h, a n d t o t a l v o l u m e o f s o i l to b e t r e a t e d. 3. S o i l t y p e a n d its i n i t i a l p r o p e r t i e s. 4. M a t e r i a l s a v a i l a b i l i t y ; e.g., s and, g r a v e l, w a t e r, a d m i x t u r e s. 5. E q u i p m e n t a n d s k i l l s a v a i l a b i l i t y. 6. E n v i r o n m e n t a l f a c t o r s w a s t e d i s p o s a l, e r o s i o n, w a t e r p o l l u t i o n, e f f e c t s o n a d j a c e n t s t r u c t u r e s a n d f a c i l i t i e s. 7. L o c a l e x p e r i e n c e a n d p r e f e r e n c e s. 8. T i m e a v a i l a b l e. 9. Cost. T h e m e t h o d s d e s c r i b e d in t h i s r e p o r t a r e s u m m a r i z e d in T a b l e X I I w h i c h c a n b e r e f e r r e d to f o r e s s e n t i a l f e a t u r e s a n d c o m p a r i s o n s. M o s t o f t h e m e t h o d s a r e b e t t e r s u i t e d to i m p r o v e m e n t o f s o m e s o i l t y p e s t h a n o t h e r s. T h i s is i l l u s t r a t e d b y Fig. 57 w h i c h r e l a t e s e a c h i m p r o v e m e n t m e t h o d to t h e r a n g e o f s o i l g r a i n s i z e s f o r w h i c h it is m o s t a p p l i c a b l e. T a b l e XIII s u m m a r i z e s c o n s i d e r a t i o n s r e l a t i n g to t h e a p p l i c a b i l i t y o f s o i l i m p r o v e m e n t f o r s u p p o r t o f s t r u c t u r e s u s i n g s h a l l o w f o u n d a t i o n s. C o s t c a n a l w a y s b e e x p e c t e d to b e a n i m p o r t a n t f a c t o r i n f l u e n c i n g t h e c h o i c e o f s o i l i m p r o v e m e n t m e t h o d i n a n y g i v e n case. C o s t c o m p a r i s o n s, o n a r e l a t i v e b a s i s, a r e g i v e n in T a b l e X I V for s e v e r a l m e t h o d s. T h e v a l u e s l i s t e d a r e a p p r o x i m a t e for g r o u n d m o d i f i c a t i o n in t h e U S A d u r i n g T h e y m a y b e s u b s t a n t i a l l y d i f f e r e n t in o t h e r p a r t s o f t h e w o r l d d e p e n d i n g o n l o c a l c o n d i t i o n s. C O N C L U S I O N U n t i l a b o u t 20 y e a r s a g o s o i l i m p r o v e m e n t m e t h o d s, w i t h t h e e x c e p t i o n o f s o i l s t a b i l i z a t i o n f o r p a v e m e n t s t r u c t u r e s, o c c u p i e d t h e a t t e n t i o n o f o n l y a f e w s p e c i a l i s t s, i n v o l v e d t h e s p o r a d i c a p p l i c a t i o n o f a r e l a t i v e l y f e w m e t h o d s, a n d w a s o f l i m i t e d c o n c e r n t o m o s t o f t h e m e m b e r s o f o u r S o c i e t y. F o r t h e r e a s o n s s t a t e d in t h e i n t r o d u c t i o n to t h i s s t a t e - o f - t h e - a r t r e p o r t, h o w e v e r, i n t e r e s t i n a n d t h e i m p o r t a n c e of s o i l i m p r o v e m e n t in g e o t e c h n i c a l c o n s t r u c t i o n h a v e e s c a l a t e d s o t h a t n o w s u c c e s s f u l, e c o n o m i c a l s o i l i m p r o v e m e n t m a y be c e n t r a l to t h e s u c c e s s o f m a n y p r o j e c t s. S e v e r a l d i f f e r e n t m e t h o d s f o r s o i l i m p r o v e m e n t h a v e b e e n r e v i e w e d in t h i s p a p e r ; e a c h h a s its a d v a n t a g e s, l i m i t a t i o n s, a n d s p e c i a l a p p l i c a t i o n s. N o n e c a n b e c o n s i d e r e d s u i t a b l e f o r the Gravel] Sand 1 Silt 1 Clay '... V ibro-com paction Blasting P articulate Grout I 1 Chem ical Grout 1 i Displacement Grout 1 1 Precompression 1 1 Heav y Tamping (dynamic consolidation)] i { Electro-osmosis f ' ' = * Reinforcem ent (tension, compression, shear) l i Thermal Treatment i : 1 A dm ixtures P a rtic le Size - mm Fig. 57 Applicable Grain Size Ranges for Different Stabilization Methods 554

47 TABLE XII SUMMARY O F S O I L I M P R O VEMENT METHODS METHOD PRINCIPLE MOST SUITABLE S O I L CONDITIONS/ T Y PES MAXIMUM E F F E CTIVE TREATMENT DEPTH SPECIAL MATERIALS REQUIRED SPECIAL EQUIPMENT REQUIRED PROPERTIES OF TREATED MATERIAL SPECIAL ADVANTAGES A ND LIMITATIONS RELATIVE COST BLASTING S h ock waves and vibrations cause liquefaction and displacement, w i t h settlement to h i g h e r density Saturated, clean sands; partly saturated sands and silts (collapsible loess) after flooding >30 m Explosives, backfill to plug drill holes, hole casings Jetting or d r i lling machine Can obtain relative d e n s i ties to 70-80%; may get variable density; timedependent strength gain Rapid, inexpensive, can treat any size areas; variable properties, no improvement near surface, dangerous L ow 3 oif) V) ir 3 M Z O OT 3 O u Cm o VIBRATORY PROBE D e n s i f ication by vibration; liquefaction induced s e t t lement under overburden S a t u r a t e d o r dry clean s and 20 m (Ineffective above 3-4 m depth) None V i b ratory p ile driver and 750 m m dia. open steel pipe C am obtain r elative d e n s i ties o f up to 80%. Ineffective in some sands Rapid, simple, good underwater; soft underlayers may damp vibrations, d i fficult to penetrate, stiff overlayers, n ot good in partly saturated soils Moderate o 6 < s: 8 a U] g H l/> Z VIBRO- COMPACTION COMPACTION PILES HEAVY T A M PING (Dynamic c o n s o l i d a tion) D e n s i f ication by vibration and c o m p action of b a c kfill material D e n s i f ication by displacement of pile volume and by vibration d uring driving R e p eated a p plicat ion of high i n t e nsity impacts at surface Cohesionless soils with less them 20% fines Loose sandy soils; partly saturated clayey soils; loess Cohesionless soils, w a ste fills, partly s a t u r a t e d soils 30 m Granular backfill, w a t e r supply >20 m Pile material (often sand o r soil plus cement mixture) 30 m (?) None Vibroflot, crane, pumps Pile driver, s p ecial sand p ile e q uipment T a mpers of up to 200 tons, high capacity crane C an obtain high relative d e n s i ties, good u niformity Can o b tain high densities, good u niformity Can obtain good improvement and r easonable u niformity Useful in saturated a nd p a rtly saturated soils, u niformity Useful in soils with fines, u n i form c o m paction, easy to check results; slow, limited improvement in u p per 1-2 m Simple, rapid, suitable for some soils w i t h fines; usable above a n d b e low water; requires control, m ust be away f rom existing structures Moderate Moderate to high Low P R E L OADING Load is a p p lied sufficiently in advance o f construction so that compression of soft soils is completed prior to development o f the site Normally consolid a t e d soft clays, silts, o r g anic deposits, c omp l e t e d sanitary landfills E a rth fill or o t h e r m a t e r i al for loading the site; sand or gravel for drainage b l a nket E a rth moving equipment; large water tanks o r vacuum drainage systems s o m e times used; settlement markers, piezometers Reduced w a t e r content and void ratio, i ncreased strength Easy, theory well developed, uniformity; requires long time (vertical drains can b e used to r e duce c o n solidation time) L ow (Moderate if vertical drains are required) g M W S0. s a. SURCHARGE FILLS F ill in excess of that required p ermanently is a p p l i e d to achieve a given amount of s e t t lement in a s h o rter time; excess fill then removed Normally c o n s o l i d ated soft clays, silts, organic deposits, c ompleted sanitary landfills E a rth fill or o t her material for loading the site; sand or gravel for drainage blanket E a rth moving e q u i p m e n t; s ettlement markers, piezometers R e d uced water content, void r atio a nd c ompressibility; increased strength F a ster than preloading without surcharge, theory well developed; e x tra material handling; can use vertical drains to reduce cons o l i dation time Moderate <J1 ai ai E L E C T R O OSMOSIS DC current causes w a t e r flow from a n ode towards cathode w h e r e it is removed Normally c o nsolid a ted silts and silty clays Anodes (usually reb ars or a l u m i n u m ), cathodes (well points o r rebars) DC p o wer supply, wiring, metering systems Reduced w a ter content and c o m p ressibi1ity, increased strength, electrochemical hardening No fill loading required, can use in c o n fined area, relatively fast; non-uniform pro- Derties between electrodes, no good in highly conductive soils High

48 556 T A B L E XII (Contd.) S U MMARY O F SOIL IMPROVEMENT METHODS M E T H O D P R I N CIPLE M O S T SUITABLE SO I L C O N D I T I O N S / T Y PES M A X IMUM EFFECTIVE T R E A T M E N T DEPTH S P E C I A L M A T ERIALS REQUIRED S P E C I A L EQUIPMENT REQUIRED PROPERTIES OF T R E A T E D MATERIAL S P E C I A L ADVANTAGES AND L I M I TATIONS RELATIVE COST PARTICULATE G R O U T I N G P e n e t r a t i o n grouting-fill soil pores w ith soil, cement, a n d / o r clay M e d i u m to coarse s and and gravel U n l i m i t e d Grout, w a t e r Mixers, tanks, pumps, h o ses Impervious, high s t r e n g t h with c e m e n t grout, eliminate l i quefaction d a nger Low cost grouts, h i g h strength; limited to c o a r s e - q r a i n e d soils, h a r d to evaluate L o west of the g r o u t systems C H E M I C A L G R O U T I N G S o l u t i o n s of two o r more c h e m icals react in soil p ores to form a gel o r a s o l i d p r e c i pitate M e d i u m silts a nd c o arser U n l i m i t e d Grout, w a t e r Mixers, tanks, pumps, hoses I mpervious, low t o high strength, eliminate l i quefaction d a nger L ow viscosity, c ontrollable g el time, g o o d w a t e r shut-off; high cost, h a r d to evaluate High to v ery high ü 2 H 3 O ût O % S B U 2 PRESSURE INJECTED LIME D I S P L A C E MENT GROUT L ime slurry i n j e c t e d to s h a l l o w depths u n der high pressure H i ghly viscous g r out acts as radial h y d r a u lic jack w hen p u m p e d in under h i g h p r e ssure E x p a n s i v e clays Soft, fineg r a i n e d soils; foundation s o ils w ith large voids o r cavities Unlimited, b ut 2-3 m usual Unlimited, b u t a few m usual Lime, water, s u r f a c t a n t Soil, cement w a t e r S l u r r y tanks, agitators, pumps, hoses B a t ching equipment, high p r e ssure pumps, h oses Lime e n c a p s u l a ted zones formed by channels r e s u l t i ng f rom cracks, root h o l e s, h y d r a u l i c fracture G r out b u lbs w i t h i n c o m p r e s s e d soil m a t r i x O n l y effective in n a r r o w range of soil c o n d itions Good for c o r r e c t ion of d i f f e r e n t ial settlements, f i lling large voids; careful c o n trol required C o m p e t i t i v e with o t h e r solutions t o expansive s oil problems L ow material, h i g h i n j e ction E L E CTRO- K I N E T I C INJECTION S t a b i l i z i n g c h e m i c a l s m o ved i n t o soil by e l e c t r o - o s m o s i s or c o l loids into p o r e s by e l e c t r o phoresis S a t u r a t e d silts, s i l t y clays (clean sands in case of c o l loid i n j e ction) U n k nown C h e m i c a l s t a b i l i z e r c o l l oidal v o i d fillers D C p o wer supply, anodes, c a t hodes Increased strength, red u c e d c o m p r e s sibility, r e d u c e d l i q u e faction potential E x i s t i n g s oil and s t r u c t u r e s n ot s ubj e c t e d to high pressures; n o good in soil w i t h high conductivity E x p e nsive JET G R O U T I N G H igh s p e e d jets at d e pth excavate, i n ject, and m ix s t a b i l i z e r w i t h soil to form c o l umns or panels Sands, silts, clays Water, s t a b i l i zing chemicals S p e c i a l jet nozzle, p u m p s, pipes a n d h o ses Solidified columns and w a lls U s e f u l in soils t h a t c a n't be permeation grouted, p r e c i s i o n in l o c ating t r e a t e d zones

49 TABLE XII (Contd.) SUMMARY O F S O I L I M P R O VEMENT METHODS, C O N TINUED M E THOD PRINCIPLE MOST SUITABLE SOIL CONDITIONS/ TYPES MAXIMUM EFFECTIVE T R E A TMENT DEPTH S P ECIAL MATERIALS REQUIRED SPECIAL EQUIPMENT REQUIRED PROPERTIES OF T R EATED MATERIAL SPECIAL ADVANTAGES AND LIMITATIONS RELATIVE COST REMOVE AND REPLACE F o u n dation soil excavated, i m p r oved by drying or admixture, and recompacted Inorganic soils 10 m (?) Admixture stabilizers Excavating, mixing, and compaction equipment, dewatering s y s t e m Increased strength and stiffness, reduced compressibility Uniform, controlled foundation soil wh e n replaced; may require large area d e w a tering High A D M I XTURES S T R U CTURAL FILLS Structural fill distributes loads to underlying soft soils Use over soft clays or organic soils, marsh deposits Sand, gravel, flyash, bottom ash, slag, expanded aggregate, c lam shell or o y s t e r shell, i n c i n erator ash Mixing and compaction equipment S oft subgrade p r o tected by structural loadb e a r i n g fill H igh strength, good load distribution to u n d e rlying soft soils L ow to high MIX-IN- PLACE P ILES A ND WALLS Lime, cement, or asphalt introduced t h r ough rotating a uger or special in-place mixer A ll soft or loose"inorganic soils >20 m Cement, lime, asphalt, or chemical stabilizer D r ill rig, rotary c utting and mixing head, additive p r o p o r t i o n ing e q u i p ment S o l i d i f i e d soil piles o r walls o f relatively high strength Uses native soil, reduced lateral s u p port requirements during excavation; d i f ficult quality control Moderate to high T H E RMAL H E A TING D r y i n g at low t e m peratures; a l t e r a tion of clays at intermediate t emp e r a tures ( C); fusion at high temperatures (>1000 C) Fine-grained soils, e s p e c i a l ly p a r t l y satur a t e d clays a nd silts, loess 15 m Fuel Fuel tanks, b u r n e r s, blowers Reduced w a ter content, p l a s ticity, w a ter sensitivity; increased strength C an obtain irreversible improvements in p r o p e r t i e s ; can introduce s t a b i lizers with hot gases H igh FREEZING Freeze soft, wet g r ound to increase its strength and s tiffness All soils Several m Refrigerant R e f r i g e r a t ion system Increased strength and stiffness; red uced p e r m e ability N o good in flowing g r ound water, temporary High V I BRO- REPLACEMENT STONE AND S AND COLUMNS Hole j e tted into soft, fine-grained s oil a nd b a c k f i lled w i t h d e n sely compacted gravel o r s a n d S oft clays and a l l uvial deposits 20 m Gravel or c r u s h e d rock backfill Vibroflot, creme or vibrocat, water Increased b e a r i n g capacity, reduced s ettlements Faster than p recompression, avoids dewatering required for rem ove and replace; l i m ited b e a r i n g capacity Moderate to high en CJl g i etu sz H sa ROOT PILES, S OIL N A I LING STRIPS, GRIDS A ND MEM BRANES Inclusions u sed to c arry tension, shear, compression Horizontal tensile strips, membranes b u r i e d in soil u n der embankments, gravel base courses and footings A ll soils? Reinforcing bars, cement g rout Cohesionless soils sane c-tf soils Can construct earth s t ructures to heights of several tens of m M etal or p l a stic strips, g eotextiles Drilling and g r outing e q u i p ment Excavating, earth h a n d ling, and compaction equipment R e i n forced zone behaves as a coherent mass S e l f - s upporting earth s t ructures, increased bearing capacity, reduced deformations In-situ r e i n forcem ent for soils that can't be g r o uted or mixedin-place with admixtures Economical, earth structures c o h e rent, can tolerate deformations; inc r e ased allowable b e a r i n g pressure M o d erate to high L ow to moderate

50 TABLE XIII A P P L I C A B I L I T Y O F F O U N D A T I O N S O I L I M P R O V E M E N T F O R D I F F E R E N T S T R U C T U R E A N D S O I L T Y P E S ( a d a p t e d f r o m W e s t, 1975) CATEGORY OF STRUCTURE STRUCTURE PERMISSIBLE SETTLEMENT LOAD INTENSITY/ USUAL BEARING PRESSURE REQUIRED, kpa (tsf) P ROBABILITY OF ADVANTAGEOUS USE OF SOIL IMPROVEMENT TECHNIQUES LOOSE COHESION- LESS SOILS SOFT ALLUVIAL DEPOSITS OLD, INORGANIC FILLS OFFICE/ APARTMENT FRAME O R LOAD- BEARING CONSTRUCTION INDUSTRIAL OTHERS High rise: More than 6 stories Medium rise: 3-6 stories Low rise: 1-3 stories Large span v/heavy machines, cranes ; process plants; power plants Framed warehouses and factories Covered storage, etor. rack systems, production areas Water and waste water treatment plants Small <25-50 mm Small <25-50 mm Small <25-50 mm Small (<25-50 mm) Differential settlement Critical High/300 + (3+) High Unlikely Low Moderate/200 (2) High Low Good Low/ (1-2) High Good High V ariable/high local concentrations to >400 (>4) High Unlikely Low Moderate Low/ (1-2) High Good High Low to moderate Low/<200 (<2) High Good High Moderate Differential settlement Important Low/<150 (<1.5) High, if required at all High High Storage tanks Moderate to high, but differential may be critical High/up to 300 (3) High, if required at all High High Open storage areas High High/up to 300 (3) High, if required at all High High Embankments and abutments Moderate to high High/up to 200 (2) High, if required at all High High T A B L E X I V C o s t C o m p a r i s o n for S e v e r a l M e t h o d s of G r o u n d M o d i f i c a t i o n s ( V alues a r e U.S. D o l l a r s f o r C o n s t r u c t i o n in t h e U. S. A. d u r i n g 1980) M e t h o d o r M a t e r i a l C o s t p e r M e t e r C o s t p e r m 2 G r o u n d S u r f a c e C o s t p e r m 3 T r e a t e d G r o u n d R e i n f o r c e d C o n c r e t e C h e m i c a l G r o u t C o m p a c t i o n G r o u t M a t e r i a l p u m p e d T r e a t e d g r o u n d E a r t h A n c h o r s D y n a m i c C o m p a c t i o n C o n c r e t e S l u r r y W a l l S l u r r y W a l l C u t o f f J e t E x c a v a t e d C u t o f f S t o n e C o l u m n s J e t G r o u t e d C o l u m n s (Data f r o m W. H. B a k e r, l e c t u r e, M a r c h 28, 1980) 558

51 s o l u t i o n of a l l p r o b l e m s in a l l soils. A s n o t e d r e c e n t l y a l s o b y S c h l o s s e r a n d J u r a n (1979), w h e n d e a l i n g w i t h t e c h n i q u e s of s o i l i m p r o v e m e n t, e x p e r i e n c e h a s a l m o s t a l w a y s p r e c e d e d t h eory. T h e r e is, t h e r e f o r e, a c o n t i n u i n g n e e d for f u r t h e r d e v e l o p m e n t of r a t i o n a l t h e o r e t i c a l a p p r o a c h e s for p r e d i c t i o n a n d e v a l u a t i o n of the d e g r e e of i m p r o v e m e n t of s t a b i l i z e d s o i l s y s t e m s b a s e d o n t h e c o n s t i t u e n t p r o p e r t i e s of t h e s o i l a n d its i n t e r a c t i o n w i t h t h e s t a b i l i z i n g m a t e r i a l s a n d p r o c e s s e s. F i v e y e a r s a g o the A S C E C o m m i t t e e o n P l a c e m e n t a n d I m p r o v e m e n t of S o i l s c o n d u c t e d a D e l p h i s u r v e y to o b t a i n o p i n i o n s f r o m e x p e r t s w o r l d w i d e o n p o s s i b l e a n d p r o b a b l e f u t u r e d e v e l o p m e n t s in s o i l i m p r o v e m e n t. T h e r e p o r t s u m m a r i z i n g t h e r e s u l t s of t h i s s u r v e y c o n c l u d e d as f o l l o w s (Bell, 1978): " A d v a n c e s in t h e a r e a s of s o i l i m p r o v e m e n t a n d p l a c e m e n t w i l l be v e r y r a p i d in t h e n e x t f i f t y y e a r s. H o w e v e r, the i n n o v a t i o n s a n d a d v a n c e s m a y p r i m a r i l y be t e c h n o l o g i c a l r a t h e r t h a n c o n c e p t u a l. M o s t a d v a n c e m e n t s w i l l be f u r t h e r d e v e l o p m e n t of m e t h o d s p r e s e n t l y a v a i l a ble. " I n g l e s (1978) p r o g n o s t i c a t e d in a s o m e w h a t s i m i lar v ein: " I m p r o v e m e n t s in m a t e r i a l s h a n d l i n g a n d d e s i g n b y m e a n s of p r o b a b i l i t y a n a l y s i s a r e s e e n to b e far t h e m o s t i m p o r t a n t a d v a n c e in t h e i m m e d i a t e f u t u r e u t i l i z a t i o n of s o i l m a t e r i a l s. M a j o r i m p r o v e m e n t in s o i l m a t e r i a l s p r o p e r t i e s is n o t to be e x p e c t e d. " In r e t r o s p e c t b o t h of t h e s e s t a t e m e n t s s e e m to t h e w r i t e r to b e s o m e w h a t s h o r t s i g h t e d. As r e c e n t l y as 15 y e a r s a g o f e w w o u l d h a v e p r e d i c t e d t h a t e a r t h r e i n f o r c e m e n t or g e o t e x t i l e s w o u l d a s s u m e m a j o r r o l e s in o u r p r a c t i c e. T e n y e a r s a g o d y n a m i c c o n s o l i d a t i o n w a s f i r s t b e i n g i n t r o d u c e d. J e t g r o u t i n g a n d m a t e r i a l s s u c h as c e m e n t b a c i l l u s w e r e j u s t b e i n g d e v e l o p e d f i v e y e a r s ago. T h e p o t e n t i a l f o r s i g n i f i c a n t a d v a n c e s in c l a y s t a b i l i z a t i o n is s t r o n g l y s u g g e s t e d b y t h e r e c e n t l y d e v e l o p e d c o m b i n e d t h e r m a l - i r o n o x i d e m e t h o d of I n g l e s a n d L i m (1980). L i k e w i s e g r o u t i n g f o r g r o u n d m o v e m e n t c o n t r o l h a s c o m e i n t o i t s o w n o n l y q u i t e r e c e n t l y. It is l i k e l y, t h e r e f o r e, t h a t i n n o v a t i o n s a n d u n a n t i c i p a t e d a d v a n c e s w i l l c o n t i n u e to be m a d e in t h e y e a r s ahead. T h e d e v e l o p m e n t of s o i l i m p r o v e m e n t m e t h o d s h a s t e n d e d to f o l l o w t w o s o m e w h a t s e p a r a t e a p p r o a c h e s. In one, e m p h a s i s h a s b e e n o n t h e i m p r o v e m e n t of the m a t e r i a l, as f o r e x a m p l e, w i t h t h e u s e of a d m i x t u r e s, t h e r m a l t r e a t m e n t, or b y d e n s i f i c a - tion. In t h e o t h e r, e m p h a s i s h a s b e e n o n t h e i m p r o v e m e n t o f t h e s y s t e m w h i c h c o n t a i n s t h e soil. E x a m p l e s of t h i s w o u l d b e r e i n f o r c e m e n t u s i n g i n c l u s i o n s. C o m b i n a t i o n s of t h e t w o m a y b e p o s s i b l e. O n e e x a m p l e w o u l d b e t h e t r e a t m e n t of a c o h e s i v e s o i l b a c k f i l l so it c o u l d be u s e d in a p e r m a n e n t r e i n f o r c e d e a r t h s t r u c t u r e. A n o t h e r m i g h t be t h e d e v e l o p m e n t of a m a t e r i a l t h a t a f t e r s e t t i n g h a s a h i g h t e n s i l e s t r e n g t h so t h a t an i n t e r l o c k e d m e s h is f o r m e d a r o u n d e n c a p s u l a t e d s e c t i o n s of s o i l a n d t h e m a s s b e h a v e s s u b s e q u e n t l y as r e i n f o r c e d earth. F i n a l l y, t w o f u r t h e r a s p e c t s o f s o i l i m p r o v e m e n t w i l l r e q u i r e c o n s i d e r a t i o n in t h e y e a r s ahead. E n e r g y c o s t s, b o t h f o r p r o d u c i n g t h e n e e d e d m a t e r i a l s a n d for c a r r y i n g o u t t h e w o r k in the f ield, w i l l b e o f i n c r e a s i n g i m p o r t a n c e. S e c o n d l y, i n c r e a s e d a t t e n t i o n s h o u l d be g i v e n to t h e l o n g t e r m f a t e of t h i n g s t h a t a r e a d d e d to t h e g r o u n d. A r e t h e r e p o t e n t i a l s for a d v e r s e e n v i r o n m e n t a l i m p a c t s? If t h e t r e a t m e n t is n o t p e r m a n e n t, w h a t p r o v i s i o n s a r e m a d e f o r r i s k s t h a t m a y d e v e l o p s u b s e q u e n t t o t h e d e s i g n life p e r i o d? A s s o i l s a n d r o c k s a r e r e s o u r c e s t h a t a r e n o t l i k e l y t o b e c o m e in s h o r t s u p p l y i n t h e y e a r s a h e a d, i n c r e a s e d c o n s t r u c t i o n on, in, a n d w i t h t h e m c a n b e a n t i c i p a t e d. T h e n e e d f o r s u i t a b l e s o i l i m p r o v e m e n t m e t h o d s w i l l c o n t i n u e to i n t e n s i f y. A C K N O W L E D G M E N T S T h e a u t h o r a p p r e c i a t e s t h e k i n d a s s i s t a n c e of m a n y c o l l e a g u e s w o r l d w i d e w h o f u r n i s h e d i n f o r m a t i o n u s e f u l f o r p r e p a r a t i o n o f t h e s t a t e - o f - t h e - a r t r e p o r t. He is p l e a s e d to a c k n o w l e d g e the s p e c i a l c o n t r i b u t i o n s m a d e b y m a n y o f the g r a d u a t e s t u d e n t s in G e o t e c h n i c a l E n g i n e e r i n g a t the U n i v e r s i t y of C a l i f o r n i a, B e r k e l e y, e s p e c i a l l y t h o s e e n r o l l e d d u r i n g 1980 in t h e c o u r s e S o i l a n d S i t e I m p r o v e m e n t. T h e i r i d e n t i f i c a t i o n, r e v i e w, a n d e v a l u a t i o n o f s i g n i f i c a n t r e c e n t r e f e r e n c e s w a s o f i n e s t i m a b l e v a l u e. T h e r e s p o n s i b i l i t y f o r t h e i n t e r p r e t a t i o n s a n d c o n c l u s i o n s p r e s e n t e d h e r e i n is, h o w e v e r, s o l e l y t h e a u t h o r 1s. 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