Prediction of Density and Strength for a Laboratory-Compacted Clay

Transcription

1 53 gs tht ws still being generted in the lndfill. 2. Settlement-time curves were found to hve shpes similr to those of fine-grined soils. 3. Strin in the snitry lndfill ws between 11 nd 14 percent for the pplied stress rnge. 4. The underlying deposits of pet nd orgnic silt exhibited strins similr to those of the overlying lndfill mterils. 5. The compression rtio for the snitry nd fill mteril, some of which ws undisturbed nd some of which ws excvted nd recompcted, ws between.16 nd.2 nd verged The observed rtes of settlement correlte well with those reported for highwy constructed on snitry lndfill in Cliforni (1) Refuse Lndfills. n Geotechnicl Prctice for isposl of Solid Wste Mterils, ASCE Specilty Conference, Ann Arbor, M, 1977, pp G.F. Sowers. Foundtion Problems in Snitry Lndfills. Journl of the Snitry Engineering ivision, ASCE, Vol. 94, No. SAl, 1968, pp R.E. Sheurs. Highwy Embnkment Construction over Snitry Lndfill. eprtment of Civil nd Environmentl Engineering, New Jersey nstitute of Technology, Newrk, J.C. Chng nd J.B. Hnnon. Settlement Performnce of Two Test Highwy Enbnkments on Snitry Lndfill. n New Horizons in Construction Mterils, Envo Publishing Co., nc., Lehigh Vlley, PA, Vol. 1, 1976, pp REFERENCES 1. S.K. Ro, L.K. Moulton, nd R.K. Sels. Settlement of Publiction of this pper sponsored by Committee on Erthwork Construction. Prediction of ensity nd Strength for Lbortory-Compcted Cly. W. WETZEL AN C. W. LOVELL Predictions of compcted soil strength for highly plstic cly re developed by sttisticlly correlting the resulu of unconsolidted undrined trixil tests with the compction vribles of wter content, dry density, nd com pctive work. Work ws clculted from mesurements of the force nd displcement of kneding-compctor foot s it loded the soil. The sttisticl models for prediction of density nd strength gve results consistent with well-documented experimentl evidence. The model for density prediction dry of optimum included vribles of wter content nd compctive work rtio; for compction wet of optimum, dry density ws function of wter content only. The model for strength prediction dry of optimum included vribles of wter content, dry density, degree of sturtion, nd confining pressure. Wet of optimum, the logrithm of strength decresed linerly with initil void rtio. All of these models hd good sttisticl vlidity. By using such models, the de1igner cn predict soil strength t prticulr compction levels or, if minimum strength vlue s required, the necessry levels of compction vlues cn be estimted. These reltions were developed from lbortory compction. Similr reltions for field compction re being developed with the intention of correlting the two. Compction is commonly used to improve the strength of embnkments, lthough the plcement specifiction usully controls only certin compction vribles. This study developed predictions of strength from compction vribles tht re more commonly nd simply mesured thn strength. The s-compcted strengths of lbortory-compcted, highly plstic cly were mesured in unconsolidted-undrined trixil tests. Smples were prepred by kneding compction to densities tht fit on three impct-energy curves, on ech of which were four wter contents. Smples were then shered t four levels of confining pressure to simulte vriety of compction conditions nd embnkment depths. n ddition, the work expended to compct the soil ws estimted from mesurements of force nd displcement for the compctor foot. The results of these tests were used in sttisticl regression nlysis to develop prediction equtions for density nd s-compcted strength in terms of the compction vribles. Correltion of these results with similr ones currently being developed for field compction will llow better control of short-term sher behvior in embnkments. Such predictions re of prticulr interest s () strength becomes more extensively used s compction specifiction element nd (b) greter ttention is pid to the potentil overloding of the compcted soil by construction equipment. LTERATURE REVEW The cly fbric estblished by compction hs n importnt effect on soil behvior. Modern fbric explntions were first introduced by Brden nd Sides (1) nd then by Hodek (2) nd his "deformble ggregte" - theory (deformble ggregte is n gglomertion of cly prticles, or mcropeds). The size nd distribution of the pore spce of compcted-cly fbric hve lso been studied considerbly in recent times. Bhsin (3) defined pore-5ize distributions for severl different clys t vrious energy levels. The distributions of the pore sizes for soil t equl porosities wet nd dry of optimum were very different: The dry smple hd lrger pores thn the wet one. n ddition, s compctive effort incresed t constnt wter content dry of optimum, the quntity of lrger pores ws vstly reduced until point ws reched t which further chnges in the pore-size distribution would not occur. These results greed with those of Sridhrn nd others (4) nd Ahmed nd others (5). Grci-Bengoche (6) lso reched similr conclusions for 5-5 silt-kolin mixture. Such studies deemphsize the role of individul cly prticles in the compction process nd focus on the nture nd ction of collections of prticles into groups clled domins, pckets, mcropeds, or ggregtes. The rrngements of these ggregtes vry significntly wet nd dry of optimum. ry of optimum, the ggregtes re distinct. The void spce is principlly between ggregtes, nd considerble quntity of it is in lrger pores. As optimum wter content is pproched, the soil gets closer to its plstic limit nd the ggregtes become more deformble. Hence, in compction the ggregtes distort p.nd squeeze together, nd this reduces the number of lrge

2 54 pores. Pst the optimum wter content, the ggregtes become much less distinct, nd the pore spce is essentilly in intr-ggregte pores, much finer rnge of sizes. At constnt wter content, increses in energy lso chnge the rrngement of ggregtes. As energy increses, ggregtes become more broken or deformed, nd the quntity of lrge pores is reduced. Rutledge (1) presented some of the first comprehensive results of unconsolidted-undrined (U-U) strength testing of compcted clys. He found tht the mjor vribles were minor principl stress, dry density, wter content, nd degree of sturtion. The U-U strengths () incresed s the minor principl stress incresed, (b) incresed s the dry density incresed, nd (c) decresed s the wter content nd sturtion incresed. The U-U strength increses with the minor principl stress only until the confining pressure becomes high enough for smple to become fully sturted. This hppens when the ir in the smple voids is dissolved in the wter s result of incresed pressure (8,9). Smples of similr fbric nd initil wter content show tht strength will increse with n increse in density. n this connection, Leonrds (1) found unique reltion between void rtio t filure nd compressive strength tht ws independent of confining pressure, dringe condition, wter content, nd degree of sturtion. At different initil wter contents, different compcted fbrics result, nd ech initil condition would hve different reltion between void rtio nd strength. cruz (11) found the differences could be ccounted for by including sturtions nd void rtio e; i.e., els. These vlues t filure plotted versus log [1/21-3)f] showed liner reltion for ll compcted smples of cruz' residul cly. Some investigtors hve used sttisticl techniques to predict sher-strength behvior. Essigmnn (12) performed unconfined compression tests on lbortory-eompcted silty cly. From list of wter content, dry density, energy, strength, nd combintions thereof, significnt vribles were selected by n ll-possible-regressions nlysis. These vribles were further combined nd nlyzed in seprte complete regression runs to obtin vlid prediction models. Similr regression techniques were used successfully by Scott (13) to formulte prediction equtions for dry density nd strength. Price (14) developed prediction equtions similr to those of Scott ri Essigmnn but by somewht different sttisticl pproch. EXPERMENTAL PROCEURE AN APPARATUS The soil used in this study ws St. Croix cly, highly plstic residul soil of sndstone nd shle origin, tken from cut re bout 6.5 km (4 miles) south of St. Croix, ndin. Atterberg limits nd clssifiction vlues determined for St. Croix cly re given below: Ctegory Unified soil clssifiction AASHTO clssifiction Atterberg limits (%) WL Wp p Cly frction, < 2 µm (%) Specific grvity (G) Clssifiction or Vlue CH A-7-6(27) Kneding compction ws used to prepre smples for trixil testing. t ws felt tht this method, mong the common lbortory types, ws the most like field compction; i.e., the shering strins nd loding ptterns tht occur in compction re more similr to those in the field. Work pplied to the soil ws mesured in terms of the lod nd displcement of the foot during compction, for every tmp pplied to the soil. etils of the instrumenttion re given elsewhere <!). Strength smples were obtined by pushing thin tubes into the compcted smple. The pprtus for mesuring volume chnge ws like tht designed by Chn nd uncn (16). t mesures the quntity of wter tht flows into nd out of the trixil cell chmber s result of chnes in the smple volume. Volume chnges of. l cm (. 61 in) could be detected. Appliction of the lod ws t constnt rte of strin of.58 mm/min (.23 in/min). This rte ws chosen to pproximte the rte used in the consolidted undrined trixil testing phse of this project (17). The trixil test ws run until the smple reched fs pek compressive strength or 2 percent xil strin, whichever cme first. SCUSSON OF RESULTS Testing Progrm The results of impct compction tests on St. Croix cly re shown in Figure 1. The three compction curves re the results of three different energy levels: modified Proctor (ASTM l557), stndrd Proctor (ASTM 698), nd low-energy Proctor ( 15-blow "stndrd Proctor"). Trixil compression smples were tested t four wter-content levels for ech energy level. These wter contents were chosen t equl sturtion levels-7.5, 77.5, 85., nd 92.5 percent-s shown in Figure 1. For ech level of density nd wter content, smples were tested t confining pressures of O, 138, 276, nd 414 kp (, 2, 4, nd 6 lbf/in'). The confining pressure of 414 kp pproximtely corresponds to the verticl pressure smple would experience t n embnkment depth of 2 m (7 ft). To sve spce in subsequent smple descriptions, code ws dopted. The confining pressure ws denoted by the letter C nd number of O, 1, 2, or 3: CO for zero confining pressure, Cl = 138 kp, C2 = 276 kp, nd C3 = 414 kp. The energy level ws represented by the letters L, s, or M, for low-energy Proctor, stndrd Proctor, nd modified Proctor, respectively. A number from one to four ccompnies this letter to define the sturtion level: l = 7. percent, 2 = 77.5 percent, 3 = 85. percent, nd 4 = 92.5 percent. The smples for trixil testing were ctully formed by kneding compction with selected foot pressures. Hence, the designtion of n energy level s modified, stndrd, or low-energy Proctor mens tht the smple ws compcted t the kneding-compction pressure required to obtin smple of selected wter content nd density on one of the impct curves. Mesurement of Work in Compction t is customry to designte the compctive work s totl vlue-i.e., the work required to operte the compction device or mchine. These vlues differ from the work required to ctully compct the soil, since they include energy lost in the mchine opertion nd work done on the soil tht does not produce residul densifiction. Thus, compctive work equls force times the residul deformtion tht produces densifiction of the soil. Mesures of foot pressure nd totl deformtion under loding with time re resonbly convenient, even with utomtic compction mchines, nd were used to represent compctive work in this study. This quntity excludes the energy lost in the compctor opertion nd in the trnsfer of energy from the compctor into the soil. t does not exclude the energy expended in nonuseful fshion to produce elstic deformtion of the soil. This work mesurement my lso include nonuseful energy for smples tht re compcted wet of optimum. When smples pproch full sturtion, verticl foot displcements my result in excessive sher displcements nd heving. The rebound nd heving losses re most significnt fter number of tmps hve cted to initilly densify the lyer of soil. Schemtic lod nd displcement curves for single

3 55 Figure 1. Results of impct compction. Modified Proctor,. Stndrd Proctor 18 o Low Energy Proctor 17 ;;.@... l Note: 1 kg/m 3 "',62 lb/ ft 3 S!urullon % Wter Content, w (%) Figure 2. Typicl lod nd displcement curves from recorder output for work msu rement. l:6dt. OO.O 34 c._jf!lme(!l _jj!lme(t) tmp of the kneding compctor re shown in Figure 2. The upper curve of the plot is the foot displcement with time; the lower curve shows foot loding with time. To determine the work done on the soil, point ws interpreted s the strt of loding, nd therefore point b ws tken s the position of the foot s it contcted the soil. Compression of the soil continued to point c, where no further downwrd movement of the foot occurred. The force ppliction within the time period to d ws considered to do compctive work. Since loding beyond point d cused no displcement, no further work ws done on the soil. The work done on the soil for this tmp cn be expressed in terms of definite increments s where t =time, F = verge force, nd d = displcement. (1) The work clculted in this wy for ech tmp ws summed for ll tmps. Although this mesure of work is superior to the nominl vlues ordinrily used, it still contins errors, s indicted bove. The differences between the verge work done t two nominl energy levels, t the sme sturtion level, re given in the following tbles (1 kj/m' = 2.9 ftlbf/ft' Nominl Energy Stu rtion Level L 1,S1 L1,M1 L2,S2 L2,M2 L3,S3 L3,M3 L4,S4 L4,M4 Energy Level L,S L,M ifference Between Averge Work (kj/m3) Averge of ifferences (J/m3) For exmple, the difference between the vere work of 11 nd Sl is 142 kj/m' (2968 ftlbf/ft ). These differences re obviously not constnt for different levels of sturtion, but they re of the sme order of mgnitude. The verge of these differences is shown in prt b [e.g., the verge difference in work between L nd M smples is 1447 kj/m' (3 242 ft lbf/ft')]. The mesured work tht ws done on the soil decresed s wter content incresed long curve of constnt nominl impct energy (Figure 1). t is not known wht compctive work is done in the impct mode. However, the nominl vlue of foot pressure in kneding compction follows the sme trend s tht of the mesured work-i.e., it decreses while nominl energy of impct compction to the sme densities remins constnt. Hence, it ppers tht impct is less efficient thn kneding compction for this plstic soil. Vrious work nd energy rtios re compred below: tem Rtio of verge work by kneding compction Rtio of verge kneding foot pressure Rtio of nominl impct energy Nominl Energy Level L S M n ech cse, the low level of work (energy) is tken s unity. The first line represents the mesured vlues of work. The second line represents simply rtio of the verge compctor-foot pressures required to fit the L, S, nd M impct curves. The third line contins the nominl energy rtios for impct compction. Since ll of these rtios re bout the sme, ny of them could be used to form compctive work rtio. The reder is reminded tht these rtios show neither the mgnitude of the compctive work nor the numericl efficiencies of the compctive modes. Unconsolidted-Undrined Sher Strength Filure conditions s function of energy level nd degree of sturtion re shown in Figures 3-5. n Figure 3, it cn be seen tht, for the low-energy Proctor level, strength decreses with incresing wter content or sturtion. At lower wter contents, the pore-wter pressures re more negtive nd so the effective stresses nd sher strengths

4 56 re higher. The smples for the stndrd nd modified energy levels shown in Figures 4 nd 5, respectively, show much the sme behvior; i.e., s wter content increses, strength decreses. However, exceptions re seen in the levels Sl nd Ml, where, t low confining pressures, the filure lines for low degrees of sturtion lie below those for higher degrees. Conlin (18) found similr behvior. The smples t low wter content nd sturtion should hve more negtive pore-wter pressures, but these re effective over lesser res nd the result is lower verge effective stress. Appliction of higher confining pressures compresses the fbric nd llows the wter to cover more soil re. The result is n increse in effective stress nd thus greter sher strength of the soil, s shown by the filure lines of Sl nd Ml t greter confining pressures. f the confining pressure is high enough, decreses in volume during testing my be gret enough to cuse lmost Figure 3. qf versus Pf for low-energy Proctor level showing filure lines. -;.. s. er 4 2 L L2 L3 L4 Nou: 1liP.1'5 lf/in p 1 ("i )/2 (kp ) Figur 4. qf venus Pf for stndrd Proctor level showing filure lines N 1' ' 2 s. S 52 S3 54,; Note: 1kPe.145 lbf/in 2 6 (kp) eoo complete sturtion. Hence, ny further increse in confining pressure increses the pressures in the pore wter, but neither the effective stresses nor the sher strength of the soil is chnged. This tendency is evident t sturtion levels 2 nd 3 of the low-energy nd stndrd Proctor filure lines in Figures 3 nd 4. The trend of the filure lines for those sme sturtion levels t the modified Proctor energy level in Figure 5 is not towrd horizontl position. The soil ggregtes of the modified Proctor smples re stiffer nd stronger (2) nd require higher confining pressures to cuse significnt volume chnge. The filure lines for sturtion level 4 for ll energy levels re quite close to the horizontl over the entire rnge of confining pressures, especilly for the low-energy level. Since three smples re lmost sturted, confining pressure hs little effect on the strength. Stress-Strin Behvior Figure 6 shows stress-strin curves from tests on four low-energy Proctor smples, shered undrined without confining pressure. The dry-of-optimum smples re stiffer, nd the smple t the lowest wter content, Ll, is quite brittle. This strin behvior is lso dependent on the volume chnges tht occur in the smple. Smples of low wter content (dry of optimum), like Ll, quickly rech the mximum mount of densifiction under sher nd begin to dilte. Pek lod is reched t or shortly fter this point. Becuse the soil ggregtes become weker nd more plstic s wter content increses from dry of optimum, they yield more before the sher strength is reched. n ddition, since wetter smples deform more under the compctor foot, the residul sher stresses re greter nd more vried in direction. Greter strin is required to mobilize sher resistnce in given direction. n ddition, becuse the ggregtes re more plstic, they will squeeze into more dense configurtion before diltion occurs. Typicl results of low-energy Proctor tests t confinement level l [138 kp (2 lbf/in 2 )) re shown in Figure 7. All of the curves demonstrte more plstic behvior, regrdless of wter content. Appliction of confining pressure cuses considerble volumetric strin nd ccompnying sher stresses between ggregtes. Agin, these sher stresses require greter strins to mobilize them ll in one direction to filure. As Figure 8 clerly shows, s confining pressure increses more densifiction occurs in dry-of-optimum smples. As these volume chnges continue to densify the smple, it is ble to pick up more lod, nd thus xil strin lso increses. Lrge confining pressures my result in enough compression to cuse the smple to pproch Figure 5. qf venus Pf for modified Proctor level showing filure lines. OOO 11 m mz '"m m 4 Nol: 1 kp =.145 lbf/in 2, BOO OOO 12 14

5 57 Fi'gure 6. Typicl stress-strin curves for tests on St. Croix cly without confinement. CO-L- o CO L.2-2 "' CO-L3 1 CO-L4- Figure 8. Wter content versus volumetric strin t filure: low-energy Proctor level. Conflnr1111,.,._.. 1 (kp) eo " ll ill..!! 1 u; ".... ".. G Figure 9. Wter content versus volumetric strin t filure: stndrd Proctor level Wter Content w ('lo) Wter Content w (%) 26 c oo U i ' '. J Note: 1kP"'.146 lbf/in Axll Strin,(%) 2. Figure 1. Wter content versus volumetric strin t filure: modified Proctor level. Figure 7. Typicl stress-strin curves for tests on St. Croix cly t confinement level ll. "' 2 ;; i! 1.! 4. Cl-L- o Cl L2 1 Cl-L! Cl-L4- " o" e.. '. " " e o '. Notll: 1 kp, 145 lbf/in 2, m e e o o o e Gt G " <' ll 1:1 complete sturtion nd leve less volume chnge to occur during undrined sher. This my be the explntion for the curves of 414 kp (6 lbf/in 2 ) in Figures 8 nd 9 crossing those of lower confining pressure. Smples wet of optimum were in ll cses close to sturtion so tht confining pressures hd no significnt effect on volumetric strin. All smples t the modified Proctor level demonstrted low volumetric strin, regrdless of wter content nd confining pressure (see Figure 1). Sttisticl Correltion The regression procedures nd criteri pplied in this study re described in detil by Weitzel (15). The vribles used to generte prediction model for-ensity included wter content, compctive work, nd the squre nd squre root of both of these. Combintions of ll vribles in products nd quotients were investigted in scttergrms. Also used ws the verge work rtio, s previously defined, nd the devition of wter content from optimum. t ws found tht, lthough overll prediction models for density both wet nd dry of optimum were cceptble in most of the sttisticl criteri, the residuls showed trends tht indicted poor fit to the observed dt. This ws cused in prt by the differences in the effect of compction work wet nd dry of optimum, s described erlier. Therefore, seprte models were developed for wter content ech side of optimum. The dry-of-optimum model selected for dry density ws Pd= v'W;tw +.32 w 2 v'w; where Pd =estimted dry density (kg/m'), WR = verge work rtio, nd w = wter content (96). t is, of course, importnt tht this eqution, nd those tht follow, not be extrpolted beyond the rnge for which dt were vilble to develop them. etils on the zones of observed dt re given by Weitzel (15). The prediction model developedfor dry density wet of optimum ws Pd= /w (3) This eqution essentilly describes line of constnt sturtion such s those in Figure 1. By definition, dry density is relted to wter content nd to sturtion S by Pd = SGpwf(Gw + S) (4) (2)

6 58 Figure 11. Predicted compressive strength versus dry density t vrious constnt wter contents dry of optimum nd confining preuures of nd 138 kp. Confining Prmn o Ntt: 1kP bf/in 2 w WlerConlenl ry Oenslly,pd (k9/m 5 ) Figure 12. Predicted compressive strength versus dry density t vrious constnt wter contents dry of optimum nd confining pressures of 276 nd 414 kp u <'7 12!! cii t 8 j 4 j... Confining Prre --w J6% w l8% w2"1. Note: 1 kp,145 lbf/in 2 l Oryenslty,pd (kg/m 5 ) where Pw = density of wter nd G = specific grvity of solids. At constnt sturtion, ll of the vribles re constnt except wter content, nd density is inversely proportionl to the wter content. The sttisticl criteri for the density models re excellent, including n R 2 of.99 (15). - The vribles tested in prediction models for strength were wter content, work, dry density, degree of sturtion, void rtio e, nd confining pressure (cr3), s well s the squres nd squre roots of these. The nerly sturted wet-<>f--optimum smples incresed little in strength with confining pressure, wheres, for resons lredy discussed, the dry-of-optimum s mples were strongly ffected by confining pressure. This mde good prediction model for strength for both wet- nd dry-of-optimum conditions unobtinble, s the residul plots for these models show. Hence, seprte models for wet nd dry of optimum were developed. The model for strength prediction dry of optimum ws qc = lpd v'si /w+ 84. (1-S;/lOO)v'U; (5) where qc = estimted compressive strength (kp), Pd = dry density (kg/m'), Si= initil degree of sturtion (%),nd cr3 = confining pressure (kp). Since initil void rtio ei is relted to wter content by Siei = wg, Eqution 5 cn be written s qc = Spd/e1v'S; + 84.(1-Si/lOOjv'Q; (6) The vrible ei /Si showed liner reltion similr to cruz dt when plotted ginst log (1-3)f/2 (.!_ ). Since the vrible Pd/ei /Si becomes higher-order term tht better linerizes the dt thn the logrithm. n ddition, the effect of confining pressure hd to be ccounted for. The vrible tht ws found to be best for this ws the term (1- Si/ 1) f3. As confining pressure increses, its effect on strength decreses (this behvior ws evident in the qr-versus-pf plots in Figures 3-5). The fctor (1- Si/ l ) reduces the influence of confining pressure s sturtion increses. Predicted compressive strength versus dry density t both constnt wter content nd constnt confining pressure for dry-of-optimum conditions is shown in Figures 11 nd 12. These figures show tht, s density increses nd/or wter content decreses, so does the strength. However, s confining pressure increses, the volume chnges increse so tht initil density hs less effect on strength. The trend of the curves t zero confining pressure is very similr to the dt of Seed nd Monismith (19). The best prediction eqution for compressive strength of smples wet of optimum ws Log(qc) = 1. 7/e; (8) The sttisticl criteri for these strength equtions re excellent (R',2:.98). The equtions cn be dpted for quick nd simple use by developing them into chrts or nomogrphs (15). Such prediction equtions cn id in embnkment design. For prticulr wter content nd work level, the compcted density tht will be obtined in compction cn be predicted. The use of this predicted density, or n observed vlue, permits the soil strength to be estimted nd the stbility of the side slopes to be clculted. Conversely, one could strt with minimum fctor ginst slope instbility nd successively "bck figure" to estimte the compction vrible vlues tht would produce it. However, the limittions on the use of lbortory-compcted smples to predict field-compcted conditions should be recognized. Work is currently under wy t Purdue University to correlte the results for lbortory-compcted smples with results for smples compcted in the field. CONCLUSONS As result of unconsolidted-undrined trixil tests performed on smples of lbortory-compcted, highly plstic St. Croix cly, the following conclusions re drwn. 1. To fit kneding-compction results to compction curves of constnt Proctor (impct) energy required less nominl energy in the kneding mode s wter content incresed. This indicted tht the kneding method is more efficient thn the impct method. 2. The vlues of clculted compctive work in kneding compction showed the sme trend s the nominl kneding vlues. 3. When the mesured vlues of work were compred for different fitted Proctor energy levels t constnt sturtion, the result ws constnt rtio. These work rtios re of the sme mgnitude s the rtios of nominl impct energy. 4. The behvior of St. Croix cly in unconsolidted-undrined trixil tests is like tht well-estblished in the literture (7-9, 18). The vlues of strength, determined t mximum stressdifference or 2 percent xil strin, decresed with wter content, (7)

7 59 incresed with density, nd incresed with confining pressure until the smple reched ner-sturtion. 5. The volume chnges tht occur during sher re significnt, especilly for smples of low wter content nd density. On the dry side of optimum, volumetric strins during sher incresed with incresed confining pressure nd decresed with incresed wter content. Volumetric strins during sher for smples wet of optimum were independent of confining pressure. 6. The prediction equtions for dry density nd strength for the rnge of vribles investigted were shown s Equtions 2, 3, 5, nd 8 in the text. These reltions re in generl greement with the reported literture (!Q,!1). 7. All developed prediction equtions hd good to excellent sttisticl chrcteristics. ACKNOWLEGMENT This reserch ws finnced by the ndin Stte Highwy Commission nd the Federl Highwy Administrtion through the Joint Highwy Reserch Project, Purdue University. We pprecite the dvice of A. G. Altscheffl of Purdue University. REFERENCES l. L. Brden nd G. R. Sides. Engineering Behvior nd Structure of Compcted Cly. Journl of the Soil Mechnics nd Foundtions ivision, ASCE, Vol. 96, No. SM4, 197, pp R.J. Hodek. Mechnism for the Compction nd Response of Kolinite. Purdue Univ., West Lfyette, N, Joint Highwy Reserch Project Rept , R.N. Bhsin. Pore Size istribution of Compcted Soils After Criticl Region rying. Purdue Univ., West Lfyette, N, Joint Highwy Reserch Project Rept. 75-3, A. Sridhrn, A.G. Altscheffl, nd S. imond. Pore Size istribution Studies. Journl of the Soil Mechnics nd Foundtions ivision, ASCE, Vol. 97, No. SM5, 1971, pp S. Ahmed, C. W. Lovell, nd S. imond. Pore Size nd Strength of Compcted Cly. Journl of the Geotechnicl Engineering ivision, ASCE, Vol. 1, GT4, 1974,pp Grci-Bengoche. The Reltion Between Permebility nd Pore Size istribution of Compcted Clyey Silts. Purdue Univ., West Lfyette, N, Joint Highwy Reserch Project Rept. 78-4, P.C. Rutledge. Coopertive Trixil Sher Reserch Progrm: Progress Report on Soil Mechnics Fct-Finding Survey. U.s. Army - Engineer Wterwys Experiment Sttion, Vicksburg, MS, A. Csgrnde nd R.C. Hirschfeld First Progress Report on nvestigtion of Stress eformtion' nd Strength Chrcteristics of Compcted Clys. Hrvrd Univ., Cmbridge, MA, Soil Mechnics Series 61, A. Csgrnde nd R.C. Hirschfeld. Second Progress Report on nvestigtion of Stress eformtion nd Strength Chrcteristics of Compcted Clys. Hrvrd Univ., Cmbridge, MA, Soil Mechnics Series 65, G.A. Leonrds. Strength Chrcteristics of Compcted Clys. Trns., ASCE, Vol. 12, Pper 278, 1955, pp P.T. Cruz. Sher Strength Chrcteristics of Some Residul Compcted Clys. Proc., 2nd Pn-Americn Conference on Soil Mechnics nd Foundtion Engineering, Brzil, Vol. l, 1963, pp M.F. Essigmnn, Jr. An Exmintion of the Vribility Resulting from Soil Compction. Purdue Univ., West Lfyette, N, Joint Highwy Reserch Project Rept , J.C. Scott. Exmintion of the Vribility of the Soked Strength of Lbortory-Compcted Cly. Purdue Univ., West Lfyette, N, Joint Highwy Reserch Project Rept. 77-8, J.T. Price. Soil Compction Specifiction Procedure for esired Field Strength Respnse. Purdue Univ., West Lfyette, N, Joint Highwy Reserch Project Rept. 78-7, W. Weitzel. The Effect of Lbortory Compction on the Unconsolidted-Undrined Strength Behvior of Highly Plstic Cly. Purdue Univ., West Lfyette, N, Joint Highwy Reserch Project Rept , Aug C.K. Chn nd J.M. uncn. A New evice for Mesuring Volume Chnges nd Pressures in Trixil Tests on Soils. Mterils Reserch nd Stndrds, Vol. 7, 1967, pp J.M. Johnson, Jr. The Effect of Lbortory Compction on the Sher Behvior of Highly Plstic Cly After Sturtion nd Consolidtion. Purdue Univ., West Lfyette, N, Joint Highwy Reserch Project Rept. 79-7, M.F. Conlin. Shering Properties of Compcted Specimens of Tylor Mrl Cly s etermined in n Unconsolidted-Undrined Trixil Test. Univ. of Texs, Austin, M. S. thesis, H.B. Seed nd C.L. Monismith. Reltionship Between ensity nd Stbility of Subgrde Soils. HRB, Bull. 93, 1954, pp Publiction of this pper sponsored by Committee on Erthwork Construction.