Missouri University of Science and Technology Scholars' Mine International Conference on Case Histories in Geotechnical Engineering (2008) - Sixth International Conference on Case Histories in Geotechnical Engineering Aug 11th - Aug 16th Seismic Response Validation of DM Treated Liquefiable Soils Raj V. Siddharthan University of Nevada, Reno, NV Ali Porbaha California State University, Sacramento, CA Follow this and additional works at: http://scholarsmine.mst.edu/icchge Part of the Geotechnical Engineering Commons Recommended Citation Siddharthan, Raj V. and Porbaha, Ali, "Seismic Response Validation of DM Treated Liquefiable Soils" (2008). International Conference on Case Histories in Geotechnical Engineering. 23. http://scholarsmine.mst.edu/icchge/6icchge/session05/23 This Article - Conference proceedings is brought to you for free and open access by Scholars' Mine. It has been accepted for inclusion in International Conference on Case Histories in Geotechnical Engineering by an authorized administrator of Scholars' Mine. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact scholarsmine@mst.edu.
SEISMIC RESPONSE VALIDATION OF DM TREATED LIQUEFIABLE SOILS Raj. V. Siddharthan University of Nevada Reno, NV 89557; USA Ali Porbaha California State University, Sacramento, CA 95819; USA ABSTRACT When structures are founded on loose saturated sandy soils, deep mixing (DM) is often an attractive remedial measure against liquefaction. The locations away from deep mixed treated area represent free-field, while strong nonlinear soil-structure interaction effects are expected around the treated area. A simplified approach that is flexible enough to accommodate important factors that affect DM treated soil sites has been recently developed. The seismic response characteristics of the DM sites have been assessed based on the residual porewater pressure response (or liquefaction) since this is a widely-used engineering response indicator. The seismic response of a DM treated field case, that is representative of the foundation under the fourteen-story Oriental Hotel building in Japan, was computed using the proposed approach. This hotel was subjected to intensive shaking during the 1995 Hyogoken-Nanbu (Kobe) Earthquake (M = 6.9) but suffered negligible damage. The proposed approach showed the effectiveness of the treated columns in reducing the porewater pressure response at locations closer to the DM treated zone. The effectiveness of treatment is significant, especially near the surface. Absence of liquefaction within the cells and at locations closer to the edge column would have played a positive role relative to the accepted performance. INTRODUCTION The remedial solutions that meet design requirements on poor quality ground are often accomplished by either improving the compressible soil found near the surface or by installing deep foundations. In many cases, when issues such as installation noise, excessive ground displacement, and bearing strata found at much deeper location etc. need to be addressed, foundation ground improvement methods are often more attractive. One such method of ground improvement is deep mixing (DM). The DM methodology has been evolving over the last three decades and extensive research has been undertaken to gain insight into different aspects of DM. Many design issues such as aspects of various construction methods and their extent of applicability (e.g., soft saturated ground), laboratory and field material characterization, and full-scale field demonstration projects have been undertaken. Many details on this technique, including its historical development, applicability, and design have been well documented by Porbaha (1998), Porbaha et al. (1998), Porbaha et al. (1999) and of O Rourke and Goh (1997), among others. Recently Siddharthan et al. (2005) and Siddharthan and Porbaha (2006) summarized available laboratory (centrifuge studies) and field evidence relative to the improvement in performance of DM treated liquefiable soils. Almost all major earthquake damage reports contain accounts of ground movements or complete failure of foundations. The most common reason for poor performance of foundations has been the loss of strength and stiffness of saturated foundation soil caused by liquefaction. It is a phenomenon that is associated with the behavior of saturated loose to medium dense cohesionless soils subjected to repeated loading. Such soils give rise to excess (or residual) porewater pressures u ex (in excess of static) and in level ground when u ex becomes equal to the initial vertical effective stress, the soil losses all its strength (i.e., liquefaction). The DM treated soils offer higher resistance relative to generation of u ex (or liquefaction). The extent of improvement has to be quantified for improved ground relative to unimproved (original) soil site to ascertain the effectiveness of the improvement. Simplified design guidelines to evaluate the extent of liquefaction and excess porewater pressure in level or gently sloping ground (unimproved soil) is readily available (Youd et al. 2001). These procedures are being routinely used by geotechnical engineers with great success to study site response. Recently, a similar design procedure has been developed to evaluate the effectiveness of DM treatment by Siddharthan et al. (2005; 2006). The applicability of their approach has been verified by centrifuge tests and a field case. Results from two series of centrifuge tests that measured porewater pressure responses in the laboratory of as many as eight DM treatment configurations tested by Babasaki et al. (1991, 1992) were used in the laboratory-based verification. This paper focuses on (1) providing details on the Paper No. 5.03 1
development of such a simplified procedure to evaluate the residual porewater pressures within and around DM soil columns, and (2) validation of the proposed approach using a well-documented field observation. The field case considered is the fourteen-story Oriental Hotel building in Japan. This hotel was subjected to intensive shaking during the 1995 Hyogoken-Nanbu (Kobe) Earthquake (M = 6.9) and extensive liquefaction and ground movement at locations near the building have been observed. This hotel site was improved by DM treatment and it survived the earthquake with little or no damage. The proposed simplified approach showed clearly the effectiveness of the treated columns in reducing the porewater pressure response at locations closer to DM treated zone. analysis of the free-field coupled with correction (or modification) factors, which are also site-specific to account for the DM treatment, seems well-suited. It should be noted that such an approach is common in other seismic soilstructure interaction problems. For example, this approach is the recommended procedure for design and analysis of underground structures such as tunnels (MCEER 1999; Hashash et al. 2001). A d b A OVERVIEW OF PROPOSED APPROACH s=b+d The DM treatment generally involves a rectangular grid (or lattice) pattern and the design dimensions such as cell width (b), thickness of treatment (d), and length or depth of treatment (L) need to be specified to achieve a desired level of improvement (Fig. 1). The figure shows the length of treatment extending to the top of a base layer with thickness H b, which in turn rests on firm ground or bedrock. The design dimensions in general are often controlled by many sitespecific issues that include design level of excitation, existing untreated soil layering and properties, equipment to be used with DM, thickness of liquefiable layers, lateral extent of treatment etc. A verified analytical procedure that is flexible enough to accommodate these variables is necessary to investigate many options before arriving at a set of optimum design dimensions (e.g., spacing, s; and thickness, d; treatment length, L etc.) for the configuration of the DM treatment. Untreated Soil Treated Soil (a) DM Treatment Plan Fill d b D s=b+d L Untreated Soil H f Treated Soil The seismic response of DM sites is quite complex and is in essence a soil-structure interaction problem. The locations away from DM treated area represent free-field, while strong soil-structure interaction effects are expected around the treated area. When liquefaction is a concern (i.e., strong enough shaking), the soil-structure interaction problem is clearly nonlinear and therefore the applicability of generalizations of soil response in terms of say, dimensionless quantities is seldom possible. This leads to the conclusion that the seismic response is essentially site-specific, which is further supported by the fact that the subsurface soil conditions (layering and soil properties etc.) in the field are rarely uniform. For realistic estimates of soil response, the varying nature of the existing subsurface field conditions needs to be accounted for as it strongly influences the soil response. It may be noted that the site response analyses, say for example simplified Seed s approach for the evaluation of liquefaction, have clearly demonstrated the importance of correctly accounting for the subsurface conditions (Youd et al. 2001). Under such circumstances, it becomes clear that an approach that incorporates a site-specific liquefaction response H b Base Layer Firm Soil or Bedrock (b) Section A-A Fig. 1. Typical configuration of deep mixing (DM). The seismic response characteristics of the DM sites are assessed based on the residual porewater pressure response (or liquefaction) since this is a widely-used engineering response indicator. Other important seismic design issues such as residual strength, permanent lateral deformation (e.g., lateral spread), and ground failure (e.g., sand boils) can be investigated based on the liquefaction analysis. The design issues listed above can be assessed based on empirical relations that have been developed specifically addressing each of these failure modes. Well-documented guidelines for such an undertaking are available in the literature and have been incorporated into many design aids such as Special Publication No. 117 developed by Division of Mines and Paper No. 5.03 2
Geology and the Southern California Earthquake Center (CDMG 1997; SCEC 1999). The steps associated with the simplified procedure of Siddharthan et al. (2005; 2006) are as follows: Step 1: Evaluate soil response of DM treated sites at various locations within and adjacent to DM treated soil and in the free-field for a variety of pre-selected test cases with different DM treatments (configurations and properties), untreated soil conditions, and excitations. The result of this investigation is the establishment of a database of residual porewater pressure response ratios (PWPRs) as a function of depth, normalized with respect to the free-field porewater pressure response at the same horizontal level. These response ratios are computed at various depths along many vertical sections (within and adjacent to DM columns). More details on this step is provided below. Step 2: Evaluate level ground seismic soil response in the free-field in terms of porewater pressure at various depths using simplified liquefaction procedures outlined by Youd et al. (2001). Unlike Step 1, this is a site-specific analysis performed for the given untreated soil mass, which is to be provided with DM treatment. This step requires many input requirements such as soil layering and properties (e.g., thicknesses, SPT values, density etc.), and excitation characteristics (e.g., acceleration strength and earthquake magnitude). Step 3: Establish residual porewater pressure ratios (PWPRs) that are appropriate for the problem under consideration based on the case-specific untreated soil conditions, DM treatment, and excitation characteristics from the database established in Step 1. Multiply the free-field responses computed in Step 2 by these equivalent factors to obtain the porewater response at various locations within and adjacent to the DM columns. As pointed out earlier, the objective of this study is to produce a simple design procedure that the practicing engineers can readily use to evaluate the effectiveness of various configurations of DM treatments. The aforementioned seismic response evaluation model is simple and realistic since it appropriately accounts for many important factors that affect the DM treated soil response. More details on the important Step 1 that relates to the database development are provided subsequently. Database of Porewater Pressure Response Ratios (PWPRs) - Step 1 The design parameters (or attributes) selected to generate the database of PWPRs are shown in Table 1. The design parameters fall under three subcategories: (1) dimensions of DM configuration and properties, (2) properties of untreated soil, and (3) characteristics of excitation. Table 1 also shows the range for these design parameters and the values subsequently selected in the response computations. The ranges listed in the table were obtained from DM soil literature and from consultation with firms that have undertaken DM treatment in the past. Total number of cases considered (see column 3 in Table 1) in the database development is 216. Table 1. Parameters used in the Database Development Design Parameter Range Selected Value(s) DM configuration and properties a) Dia. of DM columns, d 0.5-1.2 m 0.9 m b) Length of columns, L 5.5 25 m 10, 15, 25 m c) Improvement ratio, α or Separation width, b d) Max. shear modulus, G max of DM column (G dm ) 10-50% 11.1-2.7m 700 1200 MPa 15, 30, 50% 11.1, 5.1, 2.7 m 1000 MPa Properties of unsaturated soil a) Overburden fill height, 3 10 m 3 and 8 m H b) Relative density, D r 40-60% 40 and 60% Characteristics of excitation a) Max. input acceleration, a max 0.2-0.6g 0.2, 0.4, 0.6g b) Mag. of earthquake, M M = 6-8 M = 6.5, 8.0 We utilized the two-dimensional effective stress program (TARA-2M) to study the behavior of soils adjacent to the DM treated soil columns and in the free-field (Siddharthan and Norris 1990; Siddharthan and El-Gamal 1993). Past studies have recommended the use of depth (or stress-level) - dependent soil properties (shear modulus ratio, G/G max and damping, ζ) in the evaluation of soil response (EPRI 1993; Darendeli and Stokoe 2001). These recommendations were arrived at based on many laboratory tests carried out under low and high confining pressures. The soil parameters have been evaluated such that they provide best-fits to the EPRIrecommended G/G max and ζ variations. Other important model parameters are those that define the porewater pressure generation behavior. This has been extensively studied by Byrne (1991) and Ni et al. (1997). A convenient way of obtaining porewater pressure model parameters is to match a specified (target) liquefaction potential curve with the one predicted by the porewater Paper No. 5.03 3
Shear Modulus Ratio G/Gmax 1.0 0.8 0.6 0.4 0.2 0.0 EPRI Data < 52 kpa = 130-320 kpa Soil Properties Model < 52 kpa (γy=0.0004, n=0.72) = 130-320 kpa (γy=0.001, n=0.75) 0.0001 0.001 0.01 0.1 1 Shear Strain, γ (%) Cyclic Stress Ratio, τ/σ'vo 0.24 0.20 0.16 0.12 0.08 0.04 = 0.04 =(130-320 kpa) From Field Database (Youd et al. 2001) Soil Properties Model = Vertical Eff. Stress = Model Constant D r = 40 % = 0.04 < 52 kpa 0.00 1 10 100 No. of Cycles to Liquefaction or 5% Strain (a) Damping, ζ (%) 30 25 20 15 10 5 0 (a) Soil Properties Model < 52 kpa (γy=0.0004, n=0.72) = 130-320 kpa (γy=0.0007, n=0.73) EPRI Data < 52 kpa = 130-320 kpa 0.0001 0.001 0.01 0.1 1 Shear Strain, γ (%) (b) Fig. 2. Model Parameters from EPRI Recommended Material Properties for Sand: (a) G/G max and (b) ζ. pressure generation model used in the approach. The target liquefaction potential data for D r = 40% (SPT N 1 7.1) and D r = 60% (SPT N 1 16) were deduced from the widely-used field liquefaction database provided by Youd et al. (2001) in their state-of-practice report on liquefaction evaluation for level ground. The comparison between the predicted and target liquefaction potential curves for both relative densities is shown in Figs. 3a and 3b. The properties of DM soil columns are much stiffer (in excess of 10 times the soil) and were obtained from data provided by Shibuya et al. (1992) and Probaha et al. (1998). TARA-2M was used to generate a database of excess porewater pressure responses under two different excitations. The two base motions that are representative of magnitudes M = 6.5 and M = 8 were used in the study. For M = 6.5, a recording from 1983 Coalinga earthquake (M = 6.5), and for Cyclic Stress Ratio, τ/σ'vo 0.50 0.40 0.30 0.20 0.10 = 0.024 = (130-320 kpa) From Field Database (Youd et al. 2001) Soil Properties Model = Vertical Eff. Stress = Model Constant D r = 60 % = 0.024 <52 kpa 0.00 1 10 100 No. of Cycles to Liquefaction or 5% Strain (b) Fig. 3. Matching of liquefaction curves for (a) D r = 40% and (b) D r = 60%. M = 8.0, a recording from 1999 Chi Chi event were initially selected. Each of these records were spectrally matched to a target spectrum using the program RASCAL. Both of these records had a recorded maximum acceleration of about 0.6g and are designated as HPVY045 (M = 6.5) and TCU065 (M = 8) in the database maintained by the Pacific Earthquake Engineering Research (PEER) Center. The target spectra for M = 6.5 and M = 8.0 were selected based on Applied Technology Council (ATC-32) recommendation for Type D conditions. Following spectral matching, baseline correction and filtering were performed. Cut-off frequencies for the M = 6.5 record were 0.1 and 20 Hz, whereas for M = 8.0, the corresponding values were 0.15 and 20Hz. A slightly higher lower cut-off frequency was needed for M = 8.0 excitation to achieve a satisfactory baseline correction. Figure 4 shows the target ATC-32 spectra and the spectra of the selected excitations (damping 5%) for both earthquake magnitudes. The spectral matches have been very good. All motions were scaled to yield an a max of 0.2, 04, and 0.6g, and were applied at the bottom of the base layer. Paper No. 5.03 4
Normalized Spectral Acceleration 4.0 3.0 2.0 1.0 Normalized Spectral Acc. Eq. M = 8.0 Eq. M = 6.5 ATC-32 M = 6.5 (Soil D; 0.6g) ATC-32 M = 8.0 (Soil D; 0.6g) Damping = 5% 0.0 0.0 1.0 2.0 3.0 4.0 Period (Sec) Fig. 4. Target (ATC-32) and spectrally-matched response spectra for excitations with M = 6.5 and 8.0. Maximum computed porewater pressures for all excitation cases along six vertical sections located between the free-field and treated edge column and between the columns were evaluated using TARA-2M. These sections are placed near the edge column at d 1 = d, 3d and 5d; and between the DM columns at d 2 = b/4, b/2 and 3/4b. Here d and b are the thickness and clear spacing between DM columns (see Fig. 1). The computed porewater pressure responses have been normalized by dividing the responses by the corresponding computed porewater pressure at the same horizontal level in the free-field. VERIFICATION USING FIELD CASE HISTORY Porbaha et al. (1999) discussed acceptable DM treated foundation soil performance observed in the case of fourteenstory Oriental Hotel building in Japan during the 1995 Hyogoken-Nanbu (Kobe) Earthquake (M = 6.9). This building was subjected to intensive shaking during the earthquake and extensive liquefaction and ground movement at locations near the building have been observed. As shown in Fig. 5 the lattice (or grid) -type deep mixing method was applied to improve the lateral resistance of the pile foundation of this hotel. The DM treatment consists of soil-cement walls, which were founded on Holocene clay extended to 15.8 m below the ground surface through the liquefiable soil layer. The building was supported on concrete piles of 2.5 m in diameter and 33 m long. The DM walls were installed to encapsulate the piles to a depth of 15.8 m as shown in the Fig. 5. During the 1995 Hyogoken-Nanbu earthquake, the locations near the hotel experienced lateral deformations and settlement in excess of 2.3 m and 1.5 m, respectively. Such large deformations are indicative of lateral spreading in the surface fill and it was observed along many kilometers surrounding the waterfront quay facilities (Elgamal et al. 1996). This building, nevertheless, survived without damage to either the superstructure or its pile foundations, while many other buildings in the vicinity suffered severe damage. Excavation of the foundation after the earthquake indicated no sign of liquefaction or lateral flow (Suzuki et al. 1996). Input Parameters Table 2 shows the input parameters used with the proposed simplified approach to evaluate the seismic response. Many of the input values were selected from publications that provided data on the soil conditions at a well-documented instrumented down-hole array site located at the Port Island in Kobe. Madabhushi (1995) and Elgamal et al. (1996) reported on the soil layer properties that included SPT and shear wave velocity measurements at the Port Island site. Field investigations revealed that the surface layer at this reclaimed site is a fill (Masa soil) mined from nearby Rokko mountain and this layer was constructed mainly by bottom dumping from barges with no compaction, except for the upper few meters of soil above the ground water level. The surface layer consists of decomposed granite fill mixed with sand and occasional gravel. The SPT testing at the site revealed SPT values varied between 5 and 8 with representative average uncorrected value of 6.0 (Elgamal et al. 1996). Taking note of SPT impact energy level is about 15% higher in Japan than in the US, the corrected (for overburden) average SPT N 1 value for the surface fill has been estimated as, N 1 = 11.4 (1) This corresponds to an equivalent sand relative density D r of about 51%, which is within the range of relative densities considered in the database that was developed as a part of the proposed approach. The underlying clay layer on which the DM cells were founded has an average shear wave velocity of about V s = 303 m/s (Madabhushi 1995; Elgamal et al. 1996). The corresponding maximum shear modulus of the clay layer is given by, G 2 2 17.1 (303) 5 = ρvs = 1.6x10 kpa (2) 9.8 clay = The data on the stiffness of DM treated soil is not readily available. Suzuki et al. (1996) reported that the axial compressive strength of the soil-cement mix was in the order of dozens of kgf/cm 2. Paper No. 5.03 5
Fig. 5. Cement-soil mix treatment at the Oriental Hotel site, Kobe, Japan. R Q P C B A A B A Exterior DM Column L=12.2 m 3.6 m d=0.9 m 3d 5d d 5.5 m b/2 3b/4 b/4 b=5.5 m Interior DM Columns Reclaimed Fill Holocene Clay R Q P C B A A B A Fig. 6. DM configuration considered in the field case study. Assuming a conservative value of 20 kgf/cm 2 for the axial strength, an estimate of the maximum shear modulus for DM treated soil is, This value of shear modulus is consistent with the range of data on shear modulus of soil cement reported by Shibuya et al. (1992) and Porbaha et al. (1998). The average thickness (wall thickness) and the spacing within cells were estimated from Suzuki et al. (1996) as 0.9 m and 5.5 m, respectively. G dm = 2208 MPa (3) Paper No. 5.03 6
Table 2. Input Parameters Used in the Field Verification: Oriental Hotel Site. Input Parameter Properties of liquefiable surface layer Selected Value a) Unit weight, γ soil (kn/m 3 ) 19.2 b) SPT N 1 value 11.4 c) Fines content (%) 0.0 d) Thickness (m) 12.2 Properties of bottom clay layer a) Unit weight, γ clay (kn/m 3 ) 17.1 b) Max. shear modulus (kpa) 1.6x10 5 c) Fines content (%) 0.0 d) Thickness (m) 3.6 Properties of DM column a) Max. shear modulus, G dm (MPa) 2208.0 b) Thickness, d (m) 0.9 c) Length, L (m) 15.8 d) Spacing, b (m) 5.5 Characteristics of excitation a) Max. surface acceleration, a max 0.31g b) Magnitude of earthquake, M 6.9 Surface measurements of acceleration response were made at the Port Island downhole array site using a three component accelerometer. The East-West (EW) and North-South (NS) components showed maximum values of 0.28g and 0.34g, respectively (Madabhushi 1995; Elgamal et al. 1996). This means that the average maximum acceleration at the surface, which is an input to the proposed simplified approach is, ( a ) surface max = 0.31g Table 2 lists all the input values used in the prediction of soil response. Computed Porewater Pressure Ratios Maximum computed porewater pressures ratios for this field case along three vertical sections (Sections P-P, Q-Q, and R- R; see Fig. 6) located between the free-field and treated edge column are presented in Fig. 7. Only the response in the reclaimed soil is shown. For the level of excitation considered in the prediction (a max = 0.31g), the liquefaction in the free- (4) field was widespread. A closer examination of Fig. 7 reveals that the vertical section closest to the edge column (Section P- P) showed the lowest amount of porewater pressure response, while the Section R-R located the farthest showed the highest. The farthest vertical section (R-R) showed liquefaction to a depth of as much as 7 m and at other sections (P-P and Q-Q), no liquefaction was indicated. This observation indicates the effectiveness of the treated columns in reducing the porewater pressure response at locations closer to DM treated zone. The effectiveness of treatment is significant, especially near the surface. The observations relative to porewater pressure response between the treated columns can be made from Fig. 8. The vertical sections here are equally spaced at b/4, as shown in Fig. 6. In general, the following observations can be made: (1) the porewater pressure within the treated zone is smaller than those computed in the free-field, (2) the porewater pressure response is consistently lower along Section C-C, which is located closest to the edge column, (3) highest porewater pressure responses are computed near the middle of the DM columns. The reason for the third observation above can be attributed to the fact that unlike the soil elements near the DM columns, the elements away from the columns are unaffected by the presence of columns. Absence of liquefaction within the cells and at locations within up to 2.7 m from the edge column would have played a positive role relative to the accepted performance of the Oriental Hotel in the 1995 Hyogoken-Nanbu earthquake. CONCLUSIONS The paper presents a verification study undertaken to validate the applicability of a proposed simplified approach for seismic response evaluation of sites improved by deep mixing. The seismic response of a DM treated case representing the foundation under the fourteen-story Oriental Hotel building in Japan, was used as a representative field case verification. This hotel was subjected to intensive shaking during the 1995 Hyogoken-Nanbu (Kobe) Earthquake (M = 6.9) and extensive liquefaction and ground movement at locations near the building have been observed. This hotel was provided with lattice (or grid) -type deep mixing method and it survived the earthquake with little or no damage. The proposed simplified approach showed clearly the effectiveness of the treated columns in reducing the porewater pressure response at locations closer to DM treated zone. The effectiveness of treatment is significant, especially near the surface. Absence of liquefaction within the cells and at locations within up to 2.7 m from the edge column would have played a positive role relative to the accepted of the Oriental Hotel during the 1995 Hyogoken-Nanbu earthquake. The proposed simplified approach can be effectively used to analyze various DM configurations and site and excitation conditions. The soil responses are needed within and around the DM columns to Paper No. 5.03 7
ascertain the effectiveness of DM treatment and obtain an optimum design. Depth Below DM Surface, z (m) Depth Below DM Surface, z (m) Excess Porewater Pressure Ratio (u ex /s' vo ) 0 0.2 0.4 0.6 0.8 1 0 2 4 6 8 10 12 d = 0.9 m b = 5.5m Along P-P (d 1 =d) Q-Q (d 1 =3d) R-R (d 1 =5d) Surface Acc. amax = 0.31g Eq. M = 6.9 Fig. 7. Excess porewater pressure adjacent to edge DM column. Excess Porewater Pressure Ratio (u ex /s' vo ) 0 0.2 0.4 0.6 0.8 1 0 2 4 6 8 10 12 d = 0.9 m b = 5.5m Surface Acc. amax = 0.31g Eq. M = 6.9 Along A-A (d 2 =b/4) B-B (d 2 =b/2) C-C (d 2 =3b/4) Fig. 8. Excess porewater pressure within DM cell. ACKNOWLEDGEMENTS The authors would like to express their sincere appreciation to Tom Shantz of Caltrans for his help with the selection of input acceleration histories and for his valuable discussionsand suggestions relative to the formulation of the approach presented here. REFERENCES Babasaki, R., Suzuki, K., Saitoh, S., Suzuki, Y., and Kazuya, T. [1991]. Construction and Testing of Deep Mixing Foundation Improvement using the Deep Mixing method, STP-1089, ASTM, pp. 224-233. Babasaki, R., Suzuki, K., and Suzuki, Y. [1992]. Centrifuge Tests on Improved Ground for Liquefaction, Proc. 10th World Conf on Earthquake Engrg., Balkema, Rotterdam, The Netherlands, pp. 1461-1464. Byrne, P.M. [1991]. A Cyclic Shear-Volume Coupling and Pore Pressure Model for Sand, Proc., 2 nd Int. Conference on Recent advances in Geotech. Earth. Engrg. and Soil Dyn., St. Louis, Missouri, March, pp. 47-55. CDMG- [1997] Special Publication 117: Guidelines for Evaluating and Mitigation of Seismic Hazards in California, California Division of Mines and Geology. Darendeli M.B., and Stokoe, K.H. [2001]. Development of a New Family of Normalized Modulus Reduction and Material Damping Curves, Geotechnical Engineering Report GD2001 1, Geotechnical Engineering Center, Civil Engineering Department, The University of Texas at Austin. Elgamal, A.W., Zeghal, M., and Parra, E. [1996]. Liquefaction of Reclaimed Island in Kobe, Japan, J. of Geotech. Engrg.. Vol. 122(1), ASCE, pp. 39-49. EPRI [1993]. Guidelines for Determining Design Basic Ground Motions. Volume 1: Method of Guidelines for Estimating Earthquake Ground Motions in Eastern North America, Report EPRI TR-102293, November. Hashash, Y.M.A., Hook, J., Schmidt, B., and Yao, J.I.C. [2001]. Seismic Design and Analysis of Underground Structures, Tunneling and Underground Space Technology, Vol. 16, Elsevier Publication, pp. 247-293. Madabhushi, S.P.G. [1995]. Strong Motion at Port Island During the Kobe Earthquake, Cambridge University Publication CUED/D-SOILS/TR285, Cambridge, UK. Multidisciplinary Center for Earthquake Engineering Research (MCEER). [1999]. Seismic Retrofitting Manuals for Highway Systems, Volume III, Screening, Evaluation, and Retrofitting of Retaining Structures, Slopes, Tunnels, Culverts, and Pavements, Sections contributed by Power, M.S., Fishman, K., Richards, R., Makdisi, F., Musser, S., and Youd, T.L., MCEER Highway Project Task 106-G-3.2, May, Buffalo, NY. Ni, S.D., Siddharthan, R.V., and Anderson, J.G. [1997]. Characteristics of Nonlinear Response of Deep Saturated Soil Deposits, Bull. of the Seismological Soc. of America Vol. 87(2), pp. 342-355. Paper No. 5.03 8
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