EVALUATION OF RESILIENT MODULUS OF FLEXIBLE PAVEMENTS BACK - CALCULATION TECHNIQUE. A Thesis Presented to

Transcription

1 EVALUATION OF RESILIENT MODULUS OF FLEXIBLE PAVEMENTS BY BACK - CALCULATION TECHNIQUE A Thesis Presented to The Faculty of the College of Engineering and Technology Ohio University In Partial Fulfillment of the Requirements for the Degree. Master of Science in Civil Engineering by B. Viswanathan I / June 1989

2 Acknowledgement The author gratefully acknowledges the advice, support and encouragement of Dr. S. M. Sargand during the course of this thesis. He also acknowledges the help from Dr. G. A. Hazen. The author expresses his special gratitude for the help rendered by Mike Snavely of UCLS. The author expresses his thanks to Dr. M. Ahamad and Dr. J. Rectenwald to participate as members of examination Committee for this thesis. iii

3 List of figures Figure Typical dynamic force out put for Dynaflect. Moving wheel versus FWD Stress pulses. Dynaflect and geophones in operating position. Dynaflect deflection basin. Illustration of FWD. Principle of a FWD. Granular material model. Subgrade Resilient Modulus Arithmetic model. Temperature versus E for Asphalt Temperature versus Poission ratio for Asphalt. Temperature versus coefficient of Lateral pressure for Asphalt. Subgrade Material Models. FWD versus IllipaveDeflections Auglaize - Fall. Auglaize - Fall. Auglaize - Winter. Auglaize - Spring. Auglaize - Summer. Fairfi.eld - Fall. Fairfi.eld - Winter. Fairfi.eld - Spring. Fairfi.eld - Summer. Vinton - Fall. Vinton - Winter. Vinton - Spring. Vinton - Summer. Dynaflect versus IllipaveDeflections Auglaize - Fall. Auglaize - Winter. Auglaize - Spring. Fairfi.eld - Fall. Fairfi.eld - Winter. v Page

4 Fairfield - Spring. Fairfield - Summer. Vinton - Fall. Vinton - Winter. Vinton - Spring. Vinton - Summer. Auglaize - Temperature Auglaize - Rainfall Fairfield - Temperature Fairfield - Rainfall Vinton - Temperature Vinton - Rainfall Pressure versus Deflection (Auglaize). Pressure Versus Deflection (Auglaize). Pavement configuration cylindrical and rectangular half space ofan axissymmetric solid. Variation of Asphalt Modulus. Variation of Subgrade Resilient Modulus VI

5 TABLE OF CONTENTS Title page Approval page Acknowledgements List offigures List of Tables Abstract 1 ii iii v vii V111 Chapter Page IN'TRODUCTION... 1 Objective... 1 Approach... 4 Scope... 5 NDT DEVICES AND DYNAMIC DEFLECTION DATA... 7 Introduction... 7 Loading Characteristics of NDT Devices. 8 Dynaflect Falling Weight Deflectometer Representation of Deflection data BACKGROUND LITERATURE AND REVIEW Background Literature Material Properties offlexible Pavement Climatic Effects on the Resilient Behavior of Materials DATA ANALySIS Falling Weight Deflectometer Data Dynaflect Data DIIPAVE ANALySIS Description Material Models Discussion lllipave Results with FWD and DynaflecData SUMMARY CONCLUSIONS AND RESULTS... Summary Conclusions Recommendations REFERENCES Appendix!L\ iv

6 List of Tables Table to to to Comparison of nondestructive testing devices. FWD - Auglaize Fall Data. FWD - Auglaize Spring Data. FWD - Auglaize Winter Data. FWD - Auglaize Summer Data. FWD - Fairfield Fall Data. FWD - Fairfield Winter Data. FWD - Fairfield Spring Data. FWD - Fairfield Summer Data. FWD - Vinton Fall Data. FWD - Vinton Winter Data. FWD - Vinton Spring Data. FWD - Vinton Summer Data. Dyanaflect - Auglaize Data. Dynaflect - Fairfield Data. Dynaflect - Vinton Data. Input Parameters for Illipave Program. Cross section Page to to to vii

7 Abstract The resilient behavior is a significant parameter in the design, rehabilitation and serviceability of pavements. Resilient behavior is defined as the ratio of repeated deviator stress to that of recoverable strain. It has been found subgrade resilient modulus plays a vital role in the serviceability of flexible pavement and the object of this thesis to back calculate the subgrade resilient modulus of flexible pavements from data obtained from nondestructive testing using Dynaflect and Falling Weight Deflectometer (FWD) A research procedure to determine the value of resilient modulus from nondestructive data is formulated, To conduct experiments in the laboratory for arriving at the characteristics of resilient modulus is elaborate, cumbersome, time consuming and it requires advancedequipments to simulate the conditions the pavementis undergoingduring all seasons. To overcome this, nondestructive testing ofpavements is selected for obtaining the material properties for rehabilitation and reconstruction. The FWD and Dyanaflect are the nondestructive devices used in this study. The locations selected for this study are located at Auglaize, Fairfield and Vinton counties in Ohio. Nondestructive testing has been conducted on one flexible pavement at each county and the data is stored magnetic disks for analysis. Statistical analysis has been conducted for all data collected and a mean value of each sensor deflection is arrived to examine season and load variations. Using the lllipave [mite element program and lllipave models the resilient modulus of subgrade material is back-calculated based on the interpretation ofdeflection measurements obtained from nondestructive testing. In the back-calculation- technique deflection of pavements at distinct locations along the highway measured with nondestructive testing device is used as input. Soil response parameters are assumed for finite element solution. The predicted response is then compared with measured deflections and assumed values are adjusted until predicted values converge to measured deflections.the assumed parameters represent the material properties of flexible pavement when the measured and predicted deflections converge. The results provide valid presentation of structural behavior of flexible pavement and can be used effectively to evaluate nondestructive test data and determine the material properties of existing pavements for for their rehabilitation strategies. viii

8 1 CHAPTER -I INTRODUCTION 1.1 Objective One of the most important developments in the history of pavements is the use of nondestructive structural testing in selecting rehabilitation and reconstruction strategies in pavement management. The fast growing various mechanistic overlay design procedures have enhanced the scope of Non Destructive Testing (NDT). The data obtained from those tests are used for defining structural and material properties of pavements. The structural evaluation ofpavements using NDT data is a sort of inverted design process. If the pavement cross section and properties of the paving materials and subgrade soil are known, it is possible to compute the

9 pavement responses of stresses, strains and deflections under a given load at any 2 point within the pavement. In the evaluation process the response of the pavement is observed and material properties are back calculated. Of the different responses of the pavement to the load the only practical measurements are deflections. For the structural evaluation the real pavement is depicted by a mathematical model, and the measured surface deflections are used as input to back calculate the model's parameters. Most of NDT devices measure the surface deflection which is later used to evaluate the structural adequacy. Most of the overlay design procedures emerging in the eighties involve the use of deflection parameter for determining the in-situ moduli by a mathematical model or some sort ofempiricalrelationship. Based on this the material properties are obtained to represent the actual condition under which the materials are subjected and the effects ofvarious types ofdistress. It has been found that these studies are only partially successful. Additionally, the developmentofadvancedmaterial testing equipments, capable in three dimensional stress-state including cyclic loading led to new horizon of material characterization and new constitutive equations to represent the material under repetitive loading conditions. The behavior of material which are assumed as linear -elastic earlier lost theirvalidity giving way to the development ofexact constitutive relationships based on the the outcome of the experimental methods.

10 The problem faced today by pavement engineer is the inadequate 3 characterization of material properties of existing service pavements. The information is vital to assess whether the pavement is adequate to accommodate the growing traffic for future overlaying and to develop rehabilitative recommendations and maintenance strategy development based on routine structural evaluation. Here emerges the role of NDT devices which feeds an essential input in the form ofdeflections as a means of structural evaluation. To interpret this information a mechanistic pavement model is developed. In the mechanistic design procedure a structural model is used to predict pavement responses such as stresses, strains and displacements. For analyzing Ohio pavements, Illipave finite element computer program is used in this study. The Illipave structural model incorporates nonlinear, stress dependent resilient modulus material models and failure criteria for granular materials and fine grained soils. However the computational techniques of the Illipave computer program are too costly, cumbersom and complex for routine design use. (ref. 1.1, 1.2) jmilarly. the laboratory procedures are developed to simulate repetitive nature and magnitude of traffic loading to arrive at the exact material properties which are cross checked with the back calculated parameters. It is the back calculated parameters which serve as input for the design and for future evaluation.

11 4 1.2 Approach A pavement under goes deterioration with passing time and traffic The evaluation of the properties of the pavement materials with passing time and traffic and to evaluate the deterioration is by conducting laboratory tests simulating exact condition ofthe existing pavement materials or through conducting Non Destructive Testing (NDT) of pavements by obtaining the pavement deflection. Although various evaluation criteria already exist a widely accepted one has not yet been available. Primary reasons for this may be that each study was conducted under specific pavement conditions, the test loading conditions varied and various NDT devices were used in each study. In the development of a generalized acceptable evaluation criterion, it is essential to have standard Non Destructive Testing device, standard loads which best represent the actual wheel loads and the attention given to the season when the pavement is subjected to maximum distress. 1. The main study ofthis thesis is to use computer based structural evaluation systems for analyzing the NDT deflection based on the Illipave program and subsequently validating its use. 2. Development of similar computer models for Ohio pavement materials or extending the use of Illipave models for Ohio pavements. 3. Considerationand use of Dynaflectand FallingWeightDeflectometer (FWD) as NDT devices to obtain NDT data. 4. Investigatinginto the inputparametersthat influencethe deflec-

12 tion in the Illipave program Formulation of a method to streamline the uniqueness of the results. the existing overlay design. 6. Estimating in situ moduli based on Illipave anlysis. 7. Developing guide lines for implementing NDT data results in The Ohio Department of Transportation (ODOT) has been developing its highways on various types of the subgrade materials and yet there are very limited studies on the resilient behavior of subgrade. To enhance further studies the Illipave, which is a stress dependent finite element program coupled with nonlinear sub grade modeling which correlate soil properties to design parameters as modulus of resilience, modulus - stress relationship is used. 1.3 Scope The products of research presented in this report on the utility of structural evaluation methodology for pavements are based on deflection measurementfrom FWD and Dynaflectand are analyzedby the Illipavecomputerprogram and Illipave models. This report includes The use of Dynaflect and FWD for the structural evaluation followed by a brief discussion.

13 The characteristics offalling weight Deflectometer and Dynaflect 6 description and working. Current practices in the evaluation of various NDT data. Description of lllipave. The analysis with Illipave and comparison of Falling Weight Deflectometer and Dynaflect deflections with the Illipave responses. Summary, Conclusions and future recommendations based on Illi pave studies related to implementation and work.

14 7 CHAPfER 2 NDT DEVICES AND DYNAMIC DEFLECTION DATA 2.1 Introduction Deflection measurements are obtained on the top of the pavements as a response under dynamic test loadings. The forces which are produced in nondestructive testing devices are 1. Sinosoidal-steady state forces 2. Transient impulse forces. In the steady state sinusoidal forces the deflection is measured as peak to peak amplitude of the deflection signal. In the case of transient impulse forces, the maximum amplitude of the deflection signal is measured as

15 8 dynamic deflection. Although several types of NDT devices are available which produce dynamic deflection data, the Dynaflect and Falling Weight Deflectometer (FWD) which are used in the testing of pavements by the Ohio Department of Transportation are studied in detail and the description, operating characteristics are discussed in the following paragraphs. The comparison chart of various NDT devices are shown in the Table 2.1 Moreover use of a particular device is purely the choice of the user, the ease of use and the reliability and repeatability of the measurements and other characteristics considered in the selection. 2.2 Loadingchracreristics of NDT devices The deflections caused by various NDT device loadings largely result from the method of testing, magnitude and nature of applied load, time of loading and rate of loading effects. Because of the wide variations among the available NDT devices, they can be classified as 1. Static loading ':» Vehicular loading 3. Vibratory loading 4. Impulse loading All the NDT devices falls in to one of the above categories and Vibratory loading and Impulse loading are most commonly used. (ref. 2.1)

16 9 1. Static loading In the case of static loading the force is applied for several minutes at a selected location. These are like static load tests ( ASTM D and ASTM ). Also it requires large magnitude of load which cannot be interpreted as an equivalent load simulating the vehicular traffic. 2. Vehicular Loading: This relates a horizontal motion of a moving load and the testing point. A moving vehicle with reference to a fixed point in the surface initially produces zero loading, then reach a maximum and again come to zero producing similar to bell shape curve. The deflections can be measured using LVDT's. 3. Vibratory loading: These devices produce a steady state harmonic vibration of the pavement with a dynamic force generator. The response to dynamic forces is being measured with advanced electronic measuring devices. In the vibratory loading devices the location of testing is accurately fixed, the frequency function of force production remains constant with depth. They apply a static preload to the pavement which produces a reaction during vibratory phase, the response of which is measured during the steady state loading phase.

17 10 Force generation mechanisms in the vibratory testing devices: The commonly available steady state vibratory force producing mechanisms are 1. Counter rotating masses 2. Electro hydraulic systems. In the counter rotating masses the harmonic loading function is generated by the rotation of eccentric masses. The angular frequency of the loading function is equal to that of the rotating masses while its force amplitude is proportional to the square of its frequency. Without special modifications these force generating mechanism can generate and apply one force amplitude at any given frequency. The amplitude of the forces increases with frequency until the limits is reached. The typical vibrator with this type of force producing is the commercially available Dynaflect. The Dynaflect generates a peak to peak load of 1000 lbs at a driving frequency of 8Hz (fixed loading condition). Refer FIG. 2.1 In the other type electro hydraulic vibrators, the amplitude of the loading function is independent of the driving frequency. Thus any given load with in the capabilities of the vibrator can be produced at a different driving frequencies. A hydraulic pump is used to supply oil under pressure to a servo operated hydraulic actuator which creates the desired load by reaching against a large mass. The capacity of the pump, the pipe and valve systems, the reaching

18 11 mass, the pressure capacity and the rate of flow of the oil are the determinant factors of the loading system fidelity. Force Signals and accuracy checks for vibaratory devices: The force producing functions generated by vibratory devices the actual shape and amplitude are important in the understanding of the input parameters to the pavement sub-grade system and the resulting response of the system to these parameters. Bush (ref. 2.2) tested the accuracy of force for different devices by means load cells under the loading plates. Frequencies are measured from the load cells. The Dynaflect force signal at 8Hz is a smooth sinusoidal wave. Smooth forcing functions are usually produced by rotation mass force generators. 4. Impulse loading: Most impulse loading producing Non-Destructive Testing devices deliver a transient force to the pavements and measure their response. Force impulses are produced by dropping a known weight from certain fixed height on a circular plate placed in contact with pavement surface. The duration of pulse load is fixed and controlled by damping system between falling weight and contact plate.

19 12.. c e :- D Q. c o ".. Gi) JC L&J CJ U t- o LI. Static Preload Ib Tpeak.to Peak Dynamic Force 1 alooolb fa Driyin Frequency. 8 Hz Time FIG. 2.1 Typical dynamic force output for Dynaflect

20 13 Stress (KQttm 2) - -- Wt\4HM FWD AsphcJt Oem Growf -10 em -r:::::::r- -40 em Sand -loocm 54 rnsec 33 msec Js: /(; msec 33 msec msec 30msec FIG. 2.2 Moving wheel versus FWD Stress Pulses (ref. 2.3) Like the vibratory NDT Devices the pulse duration is constant with depth because of the fixed inplace nature of measurement. This is illustrated by Boh et.al (ref. 2.3). Pressure cells are placed at different depths, Bohn et.al compared the magnitude of the duration of vertical stress pulses for a moving wheel and FWD. Refer to FIG. 2.2 The commercially available impulse devices are Falling weight deflectometer and their different versions. Further detailed information is ineluded in the description of Falling Weight Deflectometer.

21 DYNAFLECT ( FIG. 2.3 ) Dynaflect is a light load NDT device. It is housed in a two wheeled trailer which contains dynamic force generator and deflection measuring systems. It can be towed by any automobile and moves on pneumatic tired wheels. The dynamic force is generated and transmitted to the pavement by lowering two 4 inch wide 16 inch outside diameter rubber covered steel wheels. Power source is obtained from the towing vehicle and the unit can be operated by the driver of the towing vehicle. As explained earlier two counter rotating eccentric masses produce steady state vibrations which are sinusoidal functions of time. It is operated at a fixed frequency of 8Hz and the magnitude of peak to peak vibratory force is 1000 lbs. Bush (ref. 2.2) who conducted a comparative study on nondestructive vibratory devices found that the measured frequency is within 3% of the indicated frequency 8Hz and the dynamic force of the dynaflect is 4% below measured force indicating frequency and amplitude of loading force are reliable. The loaded area of each steel tired wheel can be assumed as 3 Sq.inches and it

22 15 may increase in flexible pavements when the temperature is high. The force transmitted through each wheel loading is 500 lbs. In order to analyze the dynamic deflection basin the loaded area is assumed as circular of radius 1.41 inches. Five equally spaced geophones are used to measure the dynamic deflection response of the pavement. FIG. 2.3 shows the detailed arrangement of geophones. Geophones:- These are velocity transducers which gives an output in volts. The peak to peak dynamic deflection is proportional to the output voltage of geophones. All geophones before the beginning of testing are calibrated at 8Hz frequency. The complete details are available in the (ref. 2.4.) The repeatability of testing Dynaflect deflection is found to be in agreement within tolerable limits (ref. 2.4). If the measured deflection under each geophone is plotted and it forms half of the deflection basin as shown in FIG. 2.4 Testing Methodology:- (ref. 2.4) Before using Dynaflect the calibration check for each of five geophones is carried out. Geophones are placed in the calibration unit which is capable of providing repetitive vertical motion of 0.05 inch at a frequency of 8Hz. The calibrator unit is connected to the control unit. The sensor selector switch in the control unit is turned to the position of concerned geophone and

23 16 '- o t/ O.1NO.2NO.3 Loading Wheels, No.4No. 5, Geopnones (a) The Dynaflect system in operating position. Loading Wheels Geophones (b) Confiuration of load wheels and eophones. FIG. 2.3 Dynaflect and geophones in operating position (ref. 2.4)

24 17... Pavement Surface Rigid Wheels Geophones Maximum Oynoflect Deflection - w1 Surface Curvature Index, SCI- wl- w2 Base Curvature Index, BCI - w4 -ws Spreadibility, /._ IOO(w,+w 2 +w3 +w 4 +w s )/ ( 5 w1) Bosin Slope. SLOP- w t -w 5 FIG.2.4 Dynaflect deflection basin.

25 18 the respective sensitivity control is adjusted to obtain the correct deflection reading. This process is exercised for all the five geophones. Once the calibration is complete the geophones are placed back in their respective positions as shown in the FIG. 2.3 and connected to the draw bar of the Dynaflect. The drawbar's function is to raise and lower the geophones During the towing the drawbaris raised and at the desired location of testing it is lowered. (ref.2.6) The operating characteristics of testing consists of first placing geophone no.i exactly at the center between the two solid wheels which should coincide with the exact position where the pavement is to be tested. After that the Dynaflect trailer is raised to its solid steel wheels. The operating frequency is fixed to 8Hz and geophone bar is lowered to touch the surface of the pavement. The output voltage is given by in a digital read out meter directly in 1/ 1000 of an inch of vertical deflection at pavement surface and recorded by theoperator or it can be read in a H.P computer and data is stored in diskettes. After completion the geophone drawbar is raised and moved to the next location and repeated. Majidzadeh (ref.2.7, 2.8,2.9) presented a wealth of information on Dynaflect operation including trouble shootings expected and their remedies. 2.4 Falling Weight Deflectometer This belongs to impulse-load producing NDT device which induce a transient force to the pavements and measure their response. The production of impulse load is achieved by dropping a known mass from a fixed height. The mass falls on a 150 mm diameter circular plate

26 19 The production of impulse load is achieved by dropping a known mass from a fixed height. The mass falls on a 150 mm diameter circular plate connected to a rigid base plate by rubber buffers which act as springs. The design of mass configuration and spring are vital factors to produce the desired stress level, shape and time of the FWD force signal. Please refer FIG. 2.5 and FIG. 2.6 where all the details are shown clearly. The theoretical force produced is calculated by using F = "J'2mgh.k equation (1) F = Force produced in pounds-force g =Acceleration due to gravity ft/sec h = Height of the drop of the mass, feet. m =Mass offwd pounds. k = Spring constant. In FWD the load is measured by a load cell. The various versions of FWD like Danish version has been studied in detail with a moving wheel load by Bohn et al (ref. 2.3). The Swedish version of FWD employs a two mass system and gives a better smoothened shape to the force signal. The FWD deflection is in agreement with moving load is discussed by Tholen et.al.( ref. 2.10). Refer to thefig. 2.2 for a typical FWD deflection compared with a moving load. The loading signal

27 20 duration in FWD is about 25 msec lower than moving wheel load. The other capability of FWD is the application of variable loads both in low and high load ranges. The Danish version of the FWD is currently marketed in the U.S. by Dynatest as the model 8000 Dynatest Falling Weight Deflectometers. The Ohio Department of Transportation acquired model 8000 Dynatest FWD for their testing purposes. Dynatest 8000 model Falling Weight Deflectometer. Refer FIG. 2.5 and 2.6 The 8000 model Dynatest FWD is a trailer mounted NDT device can be towed by any standard passenger car or truck at regular highway speeds and it weighs about 2500 pounds. The transient pulse generating device is the trailer mounted frame capable of directing different sets of mass configurations to fall from predetermined height at right angles to the surface. By varying the Falling height a wide range peak force amplitudes as shown in equation (1). Also the mass can be varied as desired. The total assembly consists of the mass, the frame, loading plates and a buffer of shock absorbing material like rubber. The complete cycle of lifting and dropping the mass on the loading plate is based on an electro-hydraulic system. The standard features of the falling weight buffer assembly is furnished so that four different configurations of the mass can be utilized. All

28 21 four mass configurations produce a transient reproducible load pulse of approximately a half sine wave and 25 to 30 msec in duration. The drop weights are constructed so that the falling weight/buffer assembly can be changed between falling masses. The buffers are constructed so as to clearly indicate which drop weight configuration they accompany. Each of these falling weight/buffer combination is so constructed as to the capable of releasing the weight from a variable height, such that different peak loads for four specified masses are producible in the following ranges as given below. Falling Weight 110lb 220lb 440lb 660lb Peak Force bf bf bf bf For day to day testing a loading plate of 11.8 inches (or 300 mm) in diameter is used. Care should be taken to check the mass guide shaft is truly perpendicular to the road surface in the measuring mode as well as the transport.». mode. There is a load cell which can measure the load accurately. The pressure is expressed in terms of stress (psi). Seven separate deflection measurements per test can be obtained for every load level for every test. The first deflection sensing transducer or geophone measures deflection of the pavement surface through the center of the

29 22 (a) FWD in Operating Position Power source from towing vehicle Micro. HP-S'5 desk top computer FWD Trailor Manual ControlS (b) Geophones Configurotion peakl n. Force t-25msec 5 6 7, -l /3 / \.. '""". 1-12"-+-12"+ 12"-+-12"+ 12"+ 12"-1 FIG. 2.5 Illustration of FWD (ref. 2.4)

30 23 T h Loading 1 Plated dio. II.S" Geophones (No.1 is Located in a Hole 01 d Ie Center of Loading I 2/ :3 '4."' Plate ) t 4", 5 >-J... I _- I I I _ "" "." L - - Deflected Surface of Pavement Based on Peak Deflection Measured 01 each Geophone Location (a) FWD in operating position (b) Load-time history of FWD on pavement surface Peak Load r-o.025 sec FIG. 2.6 Principle of a FWD (ref. 2.4)

31 24 loading plate, which the other six transducers can be positioned along the bar which can be raised or lowered for a distance up to 7 feet. from the center of the loading plate. The deflection sensing transducer holders are spring loaded so that there is no slope between transducer and the surface being tested. An extension geophone bar is provided to measure deflection on the other side of the load plate. This is provided for the purpose of measuring load transfer characteristics in the case of rigid pavements for the joints. The unit is capable of testing in the long distance towing position by simply lowering the loading plate, mass, and seismic detector bar, subassembly to the pavement surface with controls located within the towing vehicle. There is an emergency hand pump to lift or lower the whole system. If the electronic measuring system works with a 12 volt DC power supply taken from the towing vehicle. There is Hewlettpackard model 85 computer which features a cassette tape recording/playback, CRT display and a printer for recording data from field testing and keyed-in site identification information. All operations of testing are done from the key board of the computer. OPERATIONAL PROCEDURE: testing and positioned. 1. The FWD trailer is towed on its rubber tires to the location of 2. The power supply is checked and H.P. computer is tested.

32 25 3. The mass configuration is selected using guide lines and fixed in place. 4. The site identification height, number of drops per point, coordinates are entered. When the operator enters "Run" command the whole system consists of plate, buffer, geophone bar assembly is lowered to the pavement surface. The weight is dropped 3 or 4 times as programmed from the predetermined height and after completion the whole system is raised again. 5. The whole operation just takes less than a minute. 6. Simultaneous visual inspection of deflection is displayed in HP computer terminal to arrive at a decision whether the whole process is correct. 7. The operator has the option to skip the visual display deflection is automatically shed the output on ahp 85 magnetic tape cassette together with the peak force. 2.5 REPRESENTATION OF DEFLECTION DATA: 1. Dynaflect: The peak-to-peak dynamic deflections measured by the array of five geophones in a dynaflect deflection basin (only one half is shown since the other half is a typical mirror image, FIG 2.4). The deflection basins are characterized by parameters which are functions of the deflections values of one or

33 26 more geophone readings. The theoretical deflection responses are computed at the five geophone locations by indicating their Radial distance from the center of one loading wheel. The radial distances are 10.0, 15.6, 26.0, 37.4, and 49.0 inches respectively with their first sensor at inches as shown in FIG. 2.4 The plotting of dynaflect basin in this way is very useful in comparing with FWD deflection. The usual basin parameter for structural evaluation is deflection measured at geophone no.1 also termed as Dynaflect deflection is not at at the midway between the loading wheels (at sensor no.1). Dynaflect deflection basins are plotted using the radial distance of the sensors from the center of the loaded area as the abscissa. Representation of Falling Weight Deflection Data: The radial distances of seven sensors which are available from the data are on the abscissa and the ordinates are deflection in 1/1000 ofinch. The complete review of procedures for dynamic deflections measurement by NDT methods with Dynaflect and Falling Weight Deflectometer is discussed. Both are exhaustively described. The radial distance of the deflection sensors from the load is used as abscissa and deflection measurements are used as ordinates.

34 27 Table 2.1 Minimum Device Name Principle of Operation Load (lb) Benkelmanbeam(AASHTO) Deflectionbeam NA Deflection beam (British) Deflectionbeam NA La Croix Deflectograph Mechanized Empty tru Deflection beam ck weight Dynaflect Steady state vibratory 1,000 Road rater Model400B Steady state vibratory 500 Model 2000 Steady state vibratory 1,000 Model 2008 Steady state vibratory 1,000 Falling Wt. Deflectometer KAUB 50 Impact 1,500 KAUB 150 Impact 1,500 Dynatest model 8000 Falling Wt Deflectometer Impact 1,500

35 28 Type Contact Device Name Method of Recordingdata ofprime mover Benkelmanbeam(AASHTO) Manual NA NA Deflection beam (British) Manual NA NA La Croix Deflectograph Manual, printer, None NA or automated Dynaflect Manual, printer, Tow -32 or automated vehicle Road rater Mode1400B Manual, printer, Tow 56 or automated vehicle Model 2000 Manual, printer, Tow 254 or automated vehicle Mode12008 Manual, printer, Tow 254 or automated vehicle Falling Wt. Deflectometer KAUB 50 Manual, printer, Tow 109 or automated vehicle. KAUB 150 Manual, printer, Tow 109 or automated vehicle Dynatest model 8000 Manual, printer, Tow 109 Falling Wt. Deflectometer or automated vehicle

36 29 Type of Vibratory Frequency & Load Measur ing Device name Carriage Range (hz) System Benkelmanbeam(AASHTO) NA NA None Deflectionbeam (British) NA NA None La Croix Deflectograph Truck NA None Dynaflect Trailer 8 None Road rater Model400B Trailer' 5-70 Load cell Model 2000 Trailer 5-70 Load cell Model 2008 Trailer 5-70 Load cell Falling Wt. Deflectometer KAUB 50 Trailer NA Load cell KAUB 150 Trailer NA Load cell Dynatest model 8000 Falling Wt Deflectometer Trailer NA Load cell d Earlier versions of the model 400 were mounted on vehicles.

37 30 Deflection No. of Normal Measuring Deflection Spacing of Device Name System Sensors Sensors Benkelmanbeam(AASHTO) Dial 1 NA indicator Deflection beam (British) Dial NA indicator La Croix Deflectograph Inductive 2 b NA Displacement transducers Dynaflect Velocity 5 Center &at transducers 1'intervals Road rater Mode1400B Velocity 4 Center & at transducers l' intervals Model 2000 Velocity 4 Center & at transducers l ' intervals Model 2008 Velocity 4 Center & at transducers l' intervals Falling W t. Deflectometer KAUB 50 Seismic 5 Center and deflection ft transducers

38 31 KAUB 150 Seismic 5 Center and deflection ft transducers Dynatestmodel8000 Velocity 7 Center and Falling Wt Deflectometer transducers ft b One in each wheel path. Maximum Device Name Load Actuator System Load (lb) Benkelmanbeam(AASHTO) Loaded truck axle NA Deflection beam (British) Loaded truck axle NA La Croix Deflectograph Moving truck loaded with blocks or water 9,000 Dynaflect Counterrotating 1,000 masses Road rater Model400B Hydraulic rotating 2,800 masses Model 2000 Hydraulicrotating 5,500 masses

39 32 Model 2008 Hydraulicrotating 8,000 masses Falling Wt. Deflectometer KAUB 50 Two dropping masses 12,000 KAUB 150 Two dropping masses 35,000 Dynatestmodel 8000 Falling Wt. Deflectometer Dropping masses 24,000 Type oflocal Weight on Device Name Transmission plate(lb) Benkelmanbeam(AASHTO) Truck wheels NA Deflection beam (British) Truck wheels NA La Croix Deflectograph Truck wheels NA Dynaflect Two 16-in diameter 2,100 urethane-coated steel wheels Road rater Mode1400B Two 4*7 -in pads with 2, in. center gape Model 2000 Circular plate 18-in. 3,800 diameter Model 2008 Circularplate I8-in. 5,800 diameter Falling Wt. Deflectometer KAUB 50 Sectionalizedcircular NA plate 11.8 in. dia.'

40 33 KAUB 150 Sectionalizedcircular NA plate 11.8 in. dia.f Dynatest model 8000 Falling Wt Deflectometer Circular plate 11.8 in. NA diameter 11.8" Note: 1 in. = 25.4 mm, l Ib = 4.45 N, lib = 4.5 kg, NA = not applicable C Circular plates are available. f Solid plates and plates of other dimensions are available.

41 34 CHAPTER BACKGROUND LITERATURE AND REVIEW: Based on deflections a large number of evaluation methods are in practice. This has been discussed and briefly explained like the pavement model selected, the NDT device used, the required input for analysis, the method and the output. Two to five deflection basins are considered in general and the model is linear elastic, which have two to five layers and respective moduli of elasticity are back calculated. Serivner et.al (ref. 3.1) considered the pavement on a elastic half space. He tried to match the theoretical deflection for two points 12" apart. Swift (ref 3.2) came out with a graphical technique to determine the elastic moduli of a two layered pavement by fitting a measured Dynaflect deflection basin. Cogill (ref. 3.3) developed a computer program based on a set of simultaneous equations to determine the young's moduli from surface deflection basin using coefficients obtained from layered theory computations.

42 35 Vaswani (ref. 3.4) used spreadability and maximum deflection and came out with nomographs for moduli evaluation. Majidzadeh (ref. 3.5) developed graphs to determine subgrade modulus from fifth sensor deflection of the Dynaflect and also composite moduli meant for two layers only. Moore (ref. 3.6) devised a two layer linear elastic model using point load from Dynaflect. He assumed a poisson's ration of 0.5 and fitted measured deflections to an approximate equation derived by Swift to determine the young's modulus of two layers. Paterson and Van Vuuven (ref. 3.7) came out with five layer linear elastic model, considering bottom layer of infinite depth, uniform load over a circular area using Benkleman beam deflections obtained from 8 LVDT's at various depths. In his method a iterative solution of horizontal and vertical deflections are compared with computedvalues and to determine El to E5. Wiseman (ref. 3.8) used Hogg's model with hie ratio of 10 and load is of any shape and came out with influence charts. The charts are valid for Benkleman Beam, Road Rater, and Plate bearing tests (theoretical). He compared two deflections with grapho-analytical solutions relating measured values with model parameters to determine the E for the subgrade and flexural stiffness of the upper layer.

43 36 Claessen et.al (ref. 3.9) used a three layer linear elastic model using uniform circular load and analyzed the deflections of Falling Weight deflectometer, Benkleman Beam and Deflectograph and arrived at a grapho-analytical solution similar to wiseman (ref. 3.8). Grant and Walker (ref. 3.10) model consists of three layer linear elastic, uniform load over a circular area and analyzed Benkleman Beam and curvature meter deflections. He considered the relationship between the curvature and max deflection as a function of the ratios of Young's Modulus of E2 and E3 and tried to fit the measured deflections. Koole (ref. 3.11) also devised a three layer linear elastic model using Falling Weight deflectometer. He considered the first two deflections of FWD at given distance and developed nomographs relating El, maximum deflection and the ratio between two deflections at two feet apart. Treybig (ref. 3.12) came out with nomograph using linear elastic theory for dynaflect deflections to determine the modulus of elasticity of subgrade material. Sharpe et.al (ref. 3.13) gave a graphical solution for Road Rater deflections at 0.1 and 2 feet to determine the E for the subgrade. Wiseman et.al (ref 3.14) considered Road Rater and Benkleman Beam deflections. Considering two deflections in the deflection basin, prepared a nomograph to determine the E1

44 37 and 2. In all the cases the input for the depth of each layer is provided. Thopson used Illipave program and lllipave models for Illinois flexible pavements and considered three deflections of the FWD to arrive at nomographs. (ref. 2.1) In general all these can be summarized as : 1. The use oftwo to five deflection basin values in the analysis. 2. They used linear elastic model and calculated the moduli of elasticity. 3. They are valid for a particular type of non-destructive device for a particular place and the results are extended to one or more nondestructive testing device by using some multiplication constants. The later models more or less made slight modifications on these. The severe drawbacks inherited are the exclusive use of linear elastic theory, the indiscriminant use of a wide variety of NDT loads without considering the rate of loading or comparing with actual field performance of pavements when subjected to regular vehicular loading. 3.2 MATERIAL PROPERTIES OF FLEXmLE PAVEMENT: A good performance for a flexible pavement is achieved by stability, load distribution characteristics and durability. It is essential for a design

45 38 process to acquire the exact material properties, effects introduced by loading characteristics and seasonal conditions. A number of studies which analyzed came up that assumptions made for the material properties are inadequate and it did not correspond to the actual field properties. The static field tests which were conducted to arrive at these properties didn't represent the actual loading effect the pavement is undergoing in the field. It did not account for repeated load effects that cause the pavement failure, has been hypothesized. To characterize the pavement material strength and stress-strain properties should be simulated as with service. The type of loading, state of stress, moisture content, density and temperature are some of the factors which are to be valued. Once again the results of repetitive test techniques gave an insight into the non-linear stress-strain relations and did not match the results obtained from linear theory of elasticity. The pavement deformations are divded into permanent and resilient or recoverable deformations. Distress is noticeable after a number of mixed load applications which will lead to the loss of serviceability. Due to resilient deformations the fatigue cracking occurs and the surface rutting is due to the permanent defonnations.

46 39 Various Repetitive load testing of pavement materials indicates the permanent deformation is only a small percentage of the recoverable deformation for a single load application but the permanent deformations magnifies for number of load repetitions and it amounts to a large percentage of the total deformation. The recoverable portion remains the same with number of load repetitions for a constant stress level. This is presented in (ref. 3.15, 3.16, 3.17). When summarizing, the resilient deformations of pavement structure subjected to loading are low, the permanent deformations will not the be of any concern. The stresses induced in the pavement components is within limits When the resilient deformations as a result of traffic loads are maintained low. This is shown in the studies of Allen (ref. 3.18) in the assessment of relations between states of stress and deflection under moving loads to find the performance ofpavements. The resilient modulus, defined as the repeated deviator stress (axial stress in unconfined tests divided by the recoverable strain and the resilient poisson's ratio, defined as the ratio of recoverable lateral stress to axial strain has been used to highlight the properties of granular and fine grained materials. The resilient modulus test is a repetitive load test performed in either an unconfined or triaxial state of stress. A vertical pulsating load ofcontrolled magnitude and time is applied to the sample in its z axis. The resilient modulus calculated from one set of loading condi-

47 40 tions is independent of the loading history of the material. The same specimen can be used for determining the effects on wide range of loading conditions. Again here the interpretation of test results need some mathematical modeling to represent a useful relationship between deviatoric stress versus resilient modulus. It has to be demonstrated that low deviatoric stress levels gives a high resilient modulus and high deviatoric stress gives a low resilient modulus values. To arrive at the exact value of resilient modulus the confining pressure which exist in natural conditions is around 6 psi. deviaroric stress may be able to closely match the experimental values to actual field conditions. (ref.3.30) When we look at Asphalt materials the dynamic modulus is the most common test adopted. Witczak and Yoder (ref. 3.19) defines it as the complex modulus. E is a complex number that relates stress to strain for a linear viscoelastic material subjected to a sinusoidal loading. The absolute modulus is referred as dynamic modulus. The testing procedure and equipment are well presented in (ref. 3.19) The pavement structural responses to repetitive loading is to use proper material models and the consideration of climatic and environmental effects on the resilient behavior of pavement components. Thompson (ref.3.20) has indicated the advantages of improved material and soil characterization procedure with improved structural analysis techniques in the design of flexible pavement systems. The detailed characterization of asphalt, granular and fine grained materials are presentedin the following paragraphs.

48 41 Asphaltic materials: The stress-strain relationship of asphaltic materials depends on temperature and loading duration. The asphaltic materials obey thermo-viscoelastic properties. The developmentof literature on this area is 1. Vander poel (ref. 3.21) made the initial assumption to get stiffness characteristics based on the stiffness of the bitumen and the volume concentration of the aggregate which is total volume of aggregate and bitumen. The testing procedure included both creep and dynamic tests. 2. Heukelom and Klomp (ref. 3.22) revised Vanderpoel's nomographs to arrive at better values. The problem in using all types of nomographs is they lose their validity if there is a minor variation of the assumptions based on those the nomographs are developed. 3. Shell (ref. 3.23) has come out with temperature versus modulus of elasticity of the asphalt concrete for normal highway loadings and conditions. 4. Brown (ref. 3.24) modified the shell nomograph and presented a equation to determine the modulus of asphalt 'concrete as a function of temperature vehicle speed and layer thickness in two different materials dense bitumen macamam and rolled asphalt. 5. Of all the temperature versus dynamic modulus relationships the most widely accepted and practiced is Asphalt institute equations (ref. 3.25).This relationship is used in the Illipave model. This equation is based on unconfined compression tests under sinusoidal loadings of 1,4, and 16 hz frequen-

49 42 cies at temperature of 40, 70 and 100 degree Fahrenheit. The loading time which is approximately 0.05 sec. prevailing for normal traffic loadings, asphaltic materials can be assumed to behave elastically (ref.3.24, 3..26) but the dependency on temperature cannot be ruled out. The testing carried out on asphalt cores obtained from AASHTO Road test pavement sections in Illinois under gone repetitive loading conditions to determine the dynamic modulus of asphaltic materials. The vertical stress magnitude were 30, 65 and 100 psi and where as he temperature was controlled at 40, 70 and 100 degrees fahrenheit. The change in vertical stress didn't show appreciable influence in the dynamic modulus with the variation in temperature which is ranging from 450 ksi to 1500 ksi. (ref. 3.27) This important behavior should be considered and any type of temperature correction may not reflect the actual dynamic modulus when considering a constant value for asphalt and multiplying by a coefficient to arrive at the testing temperature as most of the works are based. More over asphalt pavements when it becomes older don't necessarily reflect the original values of dynamic modulus and a suggested method is cut cores and test them and arrive at a fair relationship. The poisson's ratio of asphaltic materials has also been found to depend on temperature. It is around 0.27 at very low temperature 40 F and

50 43 increases upto 0.45 when increasing temperature. Yoder and witczak (ref. 3.19) demonstrated this in their investigations and also by several authors on the variation of poisson's ratio with temperature in the asphaltic concrete. When using lllipave model the variation of poisson's ratio show less than 5% of change in vertical deflection and a normal assumption of poisson's ratio should not deter the response of structural system of pavements when subjected NDT loads. The temperature dependent behavior of asphalt concrete plays an prominentrole to determine the critical time for pavement performance, The field studies done by chou (ref. 3.26) indicate the critical time for asphalt concrete occurs in the spring when the subgrade normally contains high moisture content and provides the least among of support and asphalt concrete is relatively cold and cannot stand large strains. Chou also suggested that when determining the pavement requirements to prevent excessive deflections in the subgrade, the stiffness in the asphalt concrete layer should be evaluated at the highest temperature expected in the field. Shell design procedure says at 95 0 F The damage to asphaltic materials to the action of environmental factors is solely due to the poor mix design. This can be avoided if proper care is taken in the rolling, compacting and designing asphaltic materials.

51 44 GRANULAR MATERIALS: The purpose of providing granular materials on a pavement is to decrease the distribution of stresses in the subgrade. They simply serve the purpose of load distributing layer when they are well compacted. When the fines passing through # 200 sieve is minimum, the moisture condition is minimum and it provides protection of the subgrade against environmental effects. On allthe tests performed on granular material and characterization of their resilient behavior, the major factors which characterize the resilient behavior of granular materials are (ref.3.28) 1. Stress level 2. Stress history 3. Frequency and duration of loading 4. Degree of saturation 5. Aggregate type and gradation 6. Density But out of all the most significant factor is the stress level. The mathematical model which closely describes the resilient modulus in terms of state on stress existing in the material is given by Er = K (0 )N