Methodology for Resilient Modulus Testing of Cohesionless Subgrades

Transcription

1 8 TRASPORTATIO RESEARCH RECORD 1406 Methodolog for Resilient Modulus Testing of Cohesionless Subgrades SoHEIL AZARIA AD MAUEL FELIBERTI Beause more emphasis is being plaed on inorporating resilient modulus testing in mehanisti pavement design, a reliable method for onduting the tests should be developed. The strengths and limitations of the resilient modulus testing proedure as applied to ohesionless subgrade soils are detailed in this paper. The overall objetives of this paper are to evaluate the aura of the resilient modulus test proedures, to modif the existing resilient modulus testing proedures as applied to granular materials, and to develop a more rigorous onstitutive model for desribing the results from resilient modulus tests. With a areful literatiire searh in the areas of dnami testing of soils as applied to transportation engineering, geotehnial engineering, and earthquake engineering, one an obtain a list of parameters that influene the results of li tests (suh as the resilient modulus tests). The ompliane of the testing devie, speimen preparation, level of deviatori stress, and the sequene and number of loading shemes are the major parameters. Through extensive testing of snth_eti speimens using state-of-the-art equipment, the aura, preision, and limitations of the proedure have been established. It was found that (a) a rigid sstem was required to minimize the ompliane effets; (b) below a deviatori stress of 2 psi, the results were questionable, and () the sequene of loading proposed b the T-274 should be extensivel modified. It was also found that the Strategi Highwa Researh Program protool suggested for granular materials ma result in exessive speimen disturbane. A newl developed proedure has been reommended herein. Given the level of emphasis in improving the resilient modulus testing proedure, it is reasonable to expet more advaned onstitutive models. representing the olleted data. A new onstitutive model was evaluated. The proposed model appears to be theoretiall more aurate and desribes the data more learl. In reent ears, resilient modulus testing has gained tremendous popularit. This inreased interest has been attributed to the new design proedure adopted in In the new design proedure, the resilient modulus of subgrade soil is onsidered as one of the most important input parameters. Sine 1986, numerous researh projets have. foused on improving the laborator proedure involved in onduting resilient modulus tests. A workshop was held at Oregon State Universit in 1989 to summarize the state of pratie in resilient modulus testing. The major onlusions of the' workshop were straightforward: 1. Using the resilient modulus as a design parameter would signifiantl improve the design proedures. S. azarian, Center for Geotehnial and Highwa Materials Researh, Universit of Texas at El Paso, El Paso, Tex M. Feliberti, California Department of Transportation, Eureka, Calif Available testing proedures were inadequate. 3. Resilient modulus testing devies needed modifiations. 4. The onstitutive models proposed were inomplete. The Strategi Highwa Researh Program (SHRP) and man state agenies (suh as those in Texas and Kentuk) have studied and suggested improved testing proedures and more advaned onstitutive models. Some of the inadequaies related to laborator testing and modeling of resilient modulus tests onduted on ohesionless subgrades are addressed in this paper. Extensive laborator tests were onduted to stud the limitations of the existing methods proposed b SHRP and using three sntheti speimens of known properties. An improved testing proedure was proposed that appears to indue the least amount of degradation and disturbane to the speimen. In addition, an improved onstitutive model was proposed for ohesionless soils. BACKGROUD Man fators affet the resilient modulus of ohesionless subgrades. Resilient modulus is equivalent to dnami modulus measured for geotehnial earthquake engineering projets. Cli triaxial tests (J) and resonant olumn tests (2) are two examples of tests tpiall used for this purpose. Dnami modulus is the most important parameter used in this field. aturall, a wealth of information is available, whih annot and should not be ignored. Based on numerous laborator tests, Hardin and Drnevih (3) proposed man parameters that affet the moduli of soils. The suggested that state of stress, void ratio, and strain amplitude are the main parameters affeting moduli measured in the laborator. Basiall, as void ratio dereases, the dnami modulus of soil inreases. One of the most important fators that affets the dnami modulus of soils is the applied onfining pressure. Hardin and Drnevih (3) onluded that a linear logarithmi relationship exists between the modulus and the applied onfining pressure. The strain level has a signifiant effet on the dnami modulus. Stokoe et al. ( 4) identified four ranges of strain amplitude. The thresholds are shown in Figure 1. The strain an be divided into four ategories: 1. Small strains-also alled elasti or low-amplitude strains, where linear behavior ours;

2 azarian and Feliberti 9 STRAI LIEAR OLIEAR PLASTIC SMALL I MEDIUM I LARGE I FAILURE ::::::::: '...J...::::::::.. :::::::::.. FAILURE - STRAI - REPETITIO STRAI RATE SOIL MODEL LIEAR I QUASI- LIEAR I PLASTIC FIGURE 1 Soil behavior and assoiated strain ranges (4). 2. Medium strains-where nonlinear elasti behavior dominates this strain range; 3. Large strains-where signifiant plasti deformation ours, but failure is not reahed; and 4. Failure strains-all greater-than-large strains. Two other threshold strains shown in the figure are the boundaries where the number of les of loads (denoted as strain repetition threshold) and strain rate of the load applied (denoted as strain rate threshold) beome important in soils. The strain rate threshold roughl oinides with the limit of the small strains, and the strain repetition is loated within medium strain level. As soon as the strain repetition threshold has passed, progressive failure will be imminent. In pavement design, the strain levels are tpiall within ranges of small strains and medium strains. Higher strains will ause almost instantaneous rutting or fatigue raking of the pavement. Several onstitutive models have been proposed for desribing the results of resilient modulus tests. For ohesionless soils, the following relationship ma be used: where k 1 and k 2 = onstants, 0 = bulk stress = 3 a + ad, a = onfining pressure, and ad = deviatori stress. This relationship is extensivel used for granular materials as reommended b. TESTIG PROCEDURES Reentl muh attention has been foused on onduting and implementing resilient modulus tests. As suh, several new testing proedures and methodologies have been developed. Seond to, SHRP is the leading organization pursuing the implementation of resilient modulus tests. SHRP has suggested some improvement to the T-274 pro- (1) edure. Based on the tpe of material to be tested, both and SHRP have proposed two separate proedures. Granular materials are tested differentl than ohesive materials. The following setions present the and SHRP proedures for testing ohesionless materials. An alternative proedure is also proposed. The resilient modulus tests were performed with a losedloop servo-valve sstem manufatured b MTS, In. The details of the equipment an be found in work b Feliberti et al. (5). An extremel rigid triaxial ell was used. Proedure The testing proedure is length beause it requires testing of the speimen under numerous stress states and loading onditions. There are 33 steps in this proedure. At eah loading step, 200 les of load are applied. The resilient modulus is alulated from the results of the 200th le. The initial six steps, whih are alled onditioning steps, would presumabl help the speimen to beome more homogeneous. In other words, during the onditioning steps, an voids in the speimen are supposedl removed and it is hoped that a good ontat between the speimen and load platens is ahieved. Data are not olleted during these steps. During this stud, the six pretesting steps resulted in unreoverable deterioration of man speimens before the atual testing. After the onditioning steps, the speimen is tested at five onfining pressures, and at eah onfining pressure, inreasing deviatori stress is applied. The deviatori stress ranges from 1 to 20 psi. During this stud, a omplete test on :me speimen (inluding preparation of the speimen) required about 4.5 hr. SHRP Proedure Contrar to 's reommendation, SHRP requires onl one onditioning step. The substantial derease in the number of pretesting steps would ertainl derease the hanes for speimen degradation or disturbane.. The atual test oa:sists of 15 loading steps. The load is applied for 0 les with the looth le being the le where the resilient modulus is alulated. The authors found this proedure eas to follow and perform. The test period for one speimen was approximatel 2.5 hr beause of fewer loading steps and fewer les of load. This proedure requires five onfining pressures with deviatori stresses from 3 to 40 psi. The authors experiened one major problem with the SHRP proedure: the speimens were disturbed due to large deviatori stresses applied at low onfining pressures. These steps result in exessive deformation of speimens, espeiall if the speimen has a low modulus. During the authors' testing program, several speimens failed before ompletion of all the loading steps. One advantage of the resilient modulus test is that it is a stage test. The speimen should not fail during testing, nor should its properties signifiantl alter between onseutive loading sequenes. As suh, the test had to be modified so that the speimen would not be subjeted to high stress levels. A new loading sequene for ohesionless soils was developed to minimize the disturbane to a speimen during testing.

3 1 TRASPORTATIO RESEARCH RECORD 1406 Proposed Proedure In the and SHRP methods, the onfining pressure is kept onstant and the deviatori stress is varied. In this proposed method, the deviatori stress is held onstant while the onfining pressure is inreased. The loading steps for the proposed proedure are shown in Table 1. The first row, where the loading sequene is 0, is the onditioning step. It is the same as for the SHRP method exept that 50 les of load are applied. The rest of the 15 loading steps are run for 0 les. A omplete test, inluding speimen preparation, takes approximatel 2 hr. Three deviatori stresses are used in this proedure. Five onfining pressures are tested at eah deviatori stress. The onfining pressures range from 3 to 20 psi. The fourth olumn speifies the number of load repetitions to appl at eah loading step, and the fifth olumn indiates whether data are olleted. The proposed method was developed to minimize the disturbane to speimens during staged testing as observed with the SHRP proedure. The stress levels are muh lower than both the and SHRP proedures. The advantages of this testing proedure over others are demonstrated later. EXPERIMETAL RESULTS Sntheti Speimens Three sntheti speimens were tested before testing atual soil speimens. The sntheti speimens were omposed of a two-omponent urethane elastomer resin ( 6). The three were named TU-700 (soft speimen), TU-900 (medium speimen), and TU-960 (hard speimen). Stokoe et al. ( 6) extensivel tested similar speimens using the stati ompression test and torsional resonant olumn test. Young's moduli obtained from the stati ompression tests for soft (TU-700), medium (TU-900), and hard (TU-960) speimens were 1,670, 6,550, and 32,300 psi, respetivel. The TABLE 1 Loading Sequene Proposed for Tpe 1 Soils Loading Deviatori Confining umber of Deformation Sequene Stress, psi Pressure, psi Repetitions Reord(Y or ) Poisson's ratios were 0.48, 0.50, and 0.47 for the soft, medium, and hard speimens, respetivel. Moduli obtained from the resonant olumn tests were also reported. Young's moduli for the soft, medium, and hard samples were 2,430,,070, and 52,000 psi, respetivel. The attributed the differene in the numbers to the loading fre-. quen. In other words, the elastomer speimens exhibited visoelasti behavior. In summar, through a rigorous series of laborator testing, Stokoe et al. ( 6) demonstrated that the elastomer speimens were exellent tools for evaluating a resilient modulus devie. Three orretion fators had to be applied to eah speimen before the aurate resilient modulus ould be found. These three orretions ompensated for (a) loading frequen, (b) testing temperature, and () mode of testing (torsional versus axial). The shear modulus of the elastomer speimens an be measured with an aura of 3 perent (6). All three speimens were approximatel 2.8 in. in diameter and 6.5 in. in height. An extensive amount of data was olleted. Basiall, eah speimen was tested following the SHRP and proedures. In addition, the proposed proedure was also evaluated. Tests were arried out seuring the speimen to the platens with and without the hdrostone grouting mix. There are several reasons for onduting suh an extensive testing program. First, an inompatibilit assoiated with the loading sequenes ould be found. Seond, the speimen is subjeted to numerous ombinations of onfining pressures and deviatori stresses. Most tests were repeated at least three times. Although not shown here, in all ases the results were repeatable and demonstrated small deviations. Tpial results from resilient modulus tests on the medium speimen (TU-900) are disussed here. The results from the other two are inluded in Feliberti et al. (5). The and SHRP results for the granular (Tpe 1) testing proedures are summarized in Figures 2( a) and 2( b), respetivel. The results from the two sets are similar. Muh satter in data is evident from the proedure due to the numerous steps involving deviatori stress levels of less than 2 psi. If the. modulus orresponding to these stress levels is ignored, the results from the SHRP and proedures are ompatible. For both ases, the modulus is unaffeted b the bulk stresses and is more or less onstant. The results from the proposed proedure are shown in Figure 2(). The results and trends are similar to those obtained from the and SHRP proedures. There is some satter in the data beause the tests were aidentall performed at deviatori stresses of slightl less than 2 psi (instead of 3 psi). The average modulus obtained from eah testing proedure is summarized in Tables 2-4 for the soft material (TU-700), medium material (TU-900), and the hard material (TU-960), respetivel. Also inluded in the tables are the standard deviation and oeffiient of variation assoiated with eah proedure. The resilient modulus values for three elastomer speimens orreted for loading frequen, temperature, and mode of vibration were determined to be 2,318 psi, 9,794 psi, and 42,083 psi, respetivel. (The sntheti speimens and their moduli were graiousl provided b the Universit of Texas at Austin.) These speimens were subjeted to similar tests,

4 azarian and Feliberti 111 TABLE 2 Summar of Results from Tests on Soft Speimen (TU-700)..._.,.... Testing Method SHRP with u. of land 2 psi without u. of land 2 psi Proposed Hdrostone Modulus Standard Deviation Coeffiient of Variation (perent) Perent Differene (perent) (a) ote: Perent Differene = Modullls from this Stud - Modullls from Torsional Tests Modullls from Torsional Tests TABLE 3 Summar of Results from Tests on Medium Speimen (TU-900) Testing Method SHRP Hdrostone Modulus 8850 Standard Deviation 256 Coeffiient Perent of Variation Differene (perent) (perent) with u. of l and 2 psi without u. of 1 and 2 psi Proposed ote: Perent Differene,;, Modullls from this Stud - Modullls from Torsional Tests Modullls from Torsional Tests (b) TABLE 4 Summar of Results from Tests on Hard Speimen (TU-960) Testing Method SHRP Hdrostone Modulus Standard Deviation 1440 Coeffiient Perent of Variation Differene (perent) (perent) with u. of land 2 psi without u. of land 2 psi Proposed IA IA IA IA ote: Perent Differene = Modullls from this Stud - Modullls from Torsional Tests Modullls from Torsional Tests () FIGURE 2 Variation in resilient modulus with bulk stress for TU-900 speimen: (a) proedure; (b) SHRP proedure; () proposed proedure. that is, torsional resonant olumn tests, reported b Stokoe et al. (6). Average moduli from different testing proedures generall ompare reasonabl well with those measured using the torsional devies. For the soft speimen, the modulus varies from a minimum of 2,4 psi to a maximum of 2,800 psi. The devie used in this stud is unable to ield onsistent results at deviatori stresses of 1 and 2 psi. If the two ases where the deviatori stresses of 1 and 2 psi were onsidered were ignored, the lower and upper bounds would hange to

5 112 2, 4 psi and 2,606 psi, respetivel. Similarl, for the medium speimens, the modulus varied between 8,850 psi and,150 psi, and for the hard speimens, between 39,860 psi and 46,270 psl. In almost all ases, the deviations in modulus from those determined from the torsional tests were within a perent range. The effets of the grouting of the speimens to the top and bottom platens were also studied. Tests were onduted on eah speimen with and without appling the hdrostone mix. The addition of the grouting agent would ensure a good ontat between the speimen and the platen. Preision mahining was required to obtain flat surfaes neessar for performing the tests without the grouting agent. In general, the variation in results among the speimens grouted and those not grouted was about perent. The variation was random. That is, in some ases, the grouted speimens ielded a higher modulus; and in other ases, the ungrouted speimens ielded a higher modulus. It seems that with the grout in plae, moduli should be equal to or greater than those of ungrouted speimens. Although extremel unlikel, it is possible that the grout had not set ompletel before the tests were performed. This would aount for some variations in the results. o reason other than random satter in data an be found for this matter. One advantage of grouting is that in some instanes, the satter in data dereases as judged b the oeffiient of variation. One again, favorable results shown here for ungrouted materials were possible after the ends of the speimens were preisel mahined. It is important that the two ends be flat and parallel. Without this preision mahining, pratiall an modulus value ould be obtained depending on the setup. The authors' onlusion is that as suggested b Pezo et al. (7), grouting the speimens is a good pratie. However, for ohesionless materials, this ma be infeasible beause the grouting agent ma flow inside the speimen. In that ase, areful preparation of the speimen would result in satisfator results. TRASPORTATIO RESEARCH RECORD 1406 of deviatori stress on speimen degradation. A more detailed testing program was onduted and an be found in work b Feliberti et al. (5). Those results, whih are not disussed here for the sake of brevit, support the onlusions drawn here. A tpial variation in modulus with bulk stress for a sand speimen using the SHRP protool is illustrated in Figure 3. The satter in the data is relativel small. Generall, the modulus inreases with the bulk stress. The data are lustered into five groups orresponding to the five different onfining pressures. Repeatabilit was heked b testing three speimens. The results were the same for the first onfining pressure. However, when the speimen was subsequentl tested at a different onfining pressure, the results obtained were errati. This indiated possible degradation of the speimen at high deviatori stresses, suggesting that the SHRP proedure might require some modifiations. Under the proposed proedure, the variation in resilient modulus with bulk stress for a sand speimen at 0 perent rd (similar to the speimen tested with the SHRP proedure) at deviatori stresses 3, 6, and 9 psi is shown in Figure 4(a). The satter in data is relativel smaller than that obtained from the SHRP method. The modulus inreases linearl with bulk stress. To demonstrate that the speimen degradation is minimal, two other speimens were tested. The first speimen was tested at deviatori stresses of 6 and 9 psi [Figure 4( b)], and the final speimen was tested at onl the deviatori stress of 9 psi (Figure 5). The modulus values at the deviatori of 9 psi for the three speimens ompare losel, as shown in Figure 5. In the authors' experiene, this degree of repeatabilit annot be ahieved with the SHRP proedure. For the first level of onfining pressures, similar results ould be ahieved. However, for the subsequent onfining pressures, the moduli would be lower, and the results would not be repeatable. After repeatabilit of results with the proposed proedure was established, two other speimens were tested at 0 perent rd These results were similar to those presented in Figure 4(a). Three tests ielded almost idential results, with moduli Sand Speimens The seond phase of the testing program onsisted of haraterizing and testing a sand ommonl found in El Paso, Texas. The properties of the sand and the development of the proposed method are desribed in this setion. The sand was first sieved with onl the fration passing through a #40 sieve and retained on a #60 sieve used for testing. This sand was extensivel used b De Lara Rio (8). The maximum and minimum unit weight for the sand were 6.9 pf and 93.2 pf, respetivel. Based on the gradatipn, the sand was lassified as A-3 b soil lassifiation and as SP in the Unified Soil Classifiation Sstem. Of the 13 speimens, 3 were tested at a relative densit (rd) of 0 perent following the SHRP testing protool, 7 were tested at a rd of 0 perent, and 3 were tested at a rd of 70 perent. The proposed proedure, not the proedure, was followed for testing in this stud. The first three speimens, with a rd of 0 perent, were tested to evaluate the proposed proedure. Eah speimen was tested at different deviatori stresses to analze the effets tti ::::ll :; "C 0 :E -;; Cl> IC 1-f FIGURE 3 Variation in resilient modulus with bulk stress for a sand speimen at a relative densit of 0 perent following SHRP proedure.

6 azarian and Feliberti 113 ;;,,; :l :; "O 0 :E ;; Cl> :l "3 "C -0 :E ';; G> IC 1 0 (a) I + 3 psi 6 psi A. 9 psi 0 I Stress Sequenes 9psi.A. 6and9psl + 3,6and9psi FIGURE 5 Comparison of variation in resilient modulus with bulk stress for three sand speimens tested at different deviatori stresses following proposed proedure. 'ij :l :; "O -0 :E 'ij ID IC (b) 1 I spsi... 9psl I with an average of about The average values for k 1 and k 2 were and 0.581, respetivel. Given the reent emphasis on improving the experimental aspets of resilient modulus tests, suh a level of orrelation ma not be adequate. As mentioned before, for a given soil, Hardin and Drnevih (3) found that two parameters signifiantl ontribute to the stiffness (modulus) of soils. These two parameters (besides void ratio) are the state of stress and the strain level. As suh, the models proposed b and SHRP diretl onsider the effets of the state of stress (bulk stress) but ignore the effets of strain amplitude. One model studied that onsiders both of these fators is in the form FIGURE 4 Variation in resilient modulus with bulk stress for a sand speimen at a relative densit of 0 perent following the proposed proedure: (a) tested at three onfining pressures; (b) tested at two onfining pressures. from the last being slightl lower. In an ase, the variation in modulus was quite small among the four speimens. Finall, three speimens were tested at a relative densit of 70 perent. Variation in modulus with bulk stress for one representative speimen at this relative densit is shown in Figure 6. The resilient modulus inreases with an inrease in bulk stress. However, some satter in the data is evident. The moduli from the three tests were within perent of eah other.,,; :l :; "O 0 :E u; ID IC 0 (2) COSTITUTIVE MODELS The onstitutive model proposed b SHRP or is presented in Equation 1. For granular materials, both SHRP and reommend a relationship between resilient modulus (MR) and bulk stress (0). For the sand material tested, using a least-squares best fit method, Equation 1 ields R-squared values from 0.78 to FIGURE 6 Variation in resilient modulus with bulk stress for a sand speimen at a relative densit of 70 perent following proposed proedure.

7 114 where k 1, k 2, and k 3 are the material onstants to be obtained from tests performed on a given soil. When the model was applied to the resilient moduli from different tests, the R squared values were generall above 0.95, exept for some isolated ases, with an average of The average values for k 1, k 2, and k 3 were , 0.668, and , respetivel. The differene between the measured modulus and alulated modulus from the /SHRP equation for the granular material (Figure 3) is shown in Figure 7(a). The figure orresponds to the modulus values obtained from three similar speimens tested at a relative densit of 0 perent. There is a signifiant differene between the atual data and the modeled data. The deviation between the two is as high as 45 perent, but it is tpiall within 30 perent. The similar plot for the same data, but for the model presented in Equation 2, is shown in Figure 7(b). The measured and alulated moduli ompare better, and the satter is usuall less than 15 perent. It should be mentioned that the tests in this stud ielded strain amplitudes in the range of - 3 to - 1 perent. There u (,) '- u Q.... ':. Gi' (,)! {a) u (,) '- u Q. - I Ill.. - (,) 0.-.,,_ ". Gi' -! (b) r--e'o FIGURE 7 Tpial variation in perent differene between measured and modeled moduli: (a) /SHRP model; (b) proposed onstitutive model. TRASPORTATIO RESEARCH RECORD 1406 fore, the above disussion is pertinent onl in this range of strains. SUMMARY AD COCLUSIOS This paper evaluates the resilient modulus testing proedure for ohesionless materials and reviews the state-of-the-art for obtaining and interpreting resilient modulus data. The initial testing proedure was proposed b and then improved b SHRP. These two approahes are evaluated. In addition, a new testing proedure for granular materials is proposed and evaluated. On the basis of tis stud, the following onlusions an be drawn: 1. The proedure for resilient modulus testing is inadequate. 2. The SHRP protool for testing granular (Tpe 1) soils indues speimen disturbane during the first level of onfining pressure. 3. The new proedure proposed here for testing granular materials appears to minimize speimen degradation and disturbane. 4. The models proposed b ma be inomplete for sands. 5. A general onstitutive model based on onsidering both state of stress and strain amplitude, whih seems more appropriate for desribing the behavior of the material tested, is introdued. ACKOWLEDGMET This work was supported b the Texas Department of Transportation. The authors greatl appreiate the support of that organization. REFERECES 1. M. L. Silver. Laborator Triaxial Testing Proedure to Determine the Cli Strength of Soils. Report UREG-31. U.S. ulear Regulator Commission, V. P. Dmevih. Reent Developments in Resonant Column Testing. Presented at Annual Meeting of the Amerian Soiet of Civil Engineering, Detroit, Mih., 1985, p B. 0. Hardin and V. P. Dmevih. Shear Modulus and Damping in Soils: Measurement and Parameters Effets. Journal of the Soil Mehanis and Foundation Division, ASCE, Vol. 98, o. SM7, 1972, pp K. H. Stokoe II, S. azarian, G. J. Rix, J. S. Salinero, J. C. Shue, and Y. J. Mok. In-Situ Testing of Hard-To-Sample Soils. Pro., Earthquake Engineering and Soil Dnamis II-Reent Advanes in Ground Motion Evaluation, ASCE, Park Cit, Utah, 1988, pp M. Feliberti, S. azarian, and T. Srinivasan. Critial Evaluation of Parameters Affeting Resilient Modulus Tests on Subgrades. Researh Report Center for Geotehnial and Highwa Materials Researh, Universit of Texas at El Paso, El Paso, Tex., K. H. Stokoe II, D. S. Kim, and R. Andres. Development of Snthetis Speimens for Calibration and Evaluation of MR

8 azarian and Feliberti Equipment. Presented at 69th Annual Meeting of the Transportation Researh Board, Washington, D.C., R. F. Pezo, G. Claros, and W. R. Hudson. An Effiient Resilient Modulus Test for Subgrades and ongranular Subbase Materials. Presented at 7lst Annual Meeting of the Transportation Researh Board, Washington, D.C., A. De Lara Rio. Evaluation of Frition Effets on the Pull-Out Capait of Horizontal Strip Anhor Plates. M.S. thesis. Department of Civil Engineering, Universit of Texas at El Paso, Publiation of this paper sponsored b Committee on Soil and Rok Properties. 115