Influence of stress ratio and moisture condition of loose deposit on dynamic parameters and ground response spectrum

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1 Jpnese Geotehnil Soiety Speil Publition The 5th Asin Regionl Conferene on Soil Mehnis n Geotehnil ngineering Influene of stress rtio n oisture onition of loose eposit on yni preters n groun response spetru Lingwei Kong i, Zhiling Sun ii, Aiguo Guo iii n Hi Tin ii i Professor, Stte Key Lbortory of Geoehnis n Geotehnil ngineering, Institute of Rok n Soil Mehnis, Chinese Aey of Sienes, Wuhn 43007, Chin. ii Ph.D. Stuent, Institute of Rok n Soil Mehnis, Chinese Aey of Sienes, Wuhn 43007, Chin. iii Assoite Professor, Institute of Rok n Soil Mehnis, Chinese Aey of Sienes, Wuhn 43007, Chin. ABSTRACT Corse-grine loose eposit, istribute wiely in erthquke-prone re in southwestern Chin, is one of the hllenging probleti geoterils. The yni sher oulus G n the ping rtio D re two in preters in seisi-hzr nlysis n one of the prinipl influening ftors ffet the yni preters is initil onitions. This pper presents stuy of the effets of initil stress rtio n oisture onition on yni sher oulus G n ping rtio D of loose eposit with lrge-sle yni trixil tests. The experientl results show tht, in the onsiere rnges of onfining pressure (σ =00kP-000kP n stress rtio (K =-3, the ry ensities of the se prepre speiens fter onsolition re well norlize with the en effetive stress σ. The xiu yni sher oulus G x is lulte using σ n the influene of ifferent onsolition stresses on initil voi rtio hs been onsiere. The test t eonstrte tht the well-known Hrin s eqution unerestites the influene of stress rtio K on G x. An iprove epiril reltion in onsiertion of the effet of stress rtio bse on Hrin s eqution is propose in the pper. It is lso onlue tht the urve of the yni sher oulus rtio G /G x versus the norlize sher strin γ n uner ir-rie onition shows ore obvious nonlinerity thn the one uner sturte onition. In ition, se stuy using the propose iprove eqution of G x n the nonliner reltionships of G /G x versus γ n is provie to illustrte the iportne of onsiering stress rtio n oisture onition in the response spetru nlysis of groun. Keywors: loose eposit, yni sher oulus, stress rtio, oisture onition, response spetru of groun INTRODUCTION Corse-grine loose eposit istribute wiely in erthquke-prone re in southwestern Chin, is one of the hllenging probleti geoterils. In My2, 2008, the Wenhun erthquke hllenge engineers to enhne their unerstning of the seisi behvior of loose eposit. The yni sher oulus G n ping rtio D re two funentl preters in yni response nlysis. For loose eposit slope, the vrious initil stti stress rtio n oisture onitions re two jor ftors ffeting the seisi response. In the pst five ees, the effets of initil stti stress rtio on sll strin sher oulus for soils hve been investigte n soe stuies suggeste tht the stress rtio hs inor influene on sher oulus(hrin n Blk 966; Sully n Cpnell 995; Hoque n Ttsuok 2004, others suggeste tht the stress rtio hs signifint influene on sher oulus(yu n Rihrt 984; Chien n Oh 2002;Sun n Yun In oisture onition, Wu et l. (984 reporte tht the sll strin sher oulus rpily inrese fro the vlue t ry onition to pek vlue orresponing to n optiu egree of sturtion, therefter slowly erese s the inrese of egree of sturtion. The pek vlue of sher oulus is lost 2 ties tht of sturte n ry onition. Siilrly, Qin n Gry (993 foun tht the existene of the pillrity n signifintly inrese the sher oulus t sll strin of sns. Vssllo et l(2007 lso foun tht the sution history of silt hs gret effet on the sher oulus t sll strin. Nowys, the effets of stress rtio n oisture onition on sher oulus t sll-strin re fr fro the lst wor. To stuy the influenes of stress rtio n oisture stte on yni sher oulus n ping rtio of loose eposits, lrge-sle yni trixil tests were rrie out n n iprove epiril reltion bse on Hrin s eqution is propose. A se stuy using the propose iprove eqution of G x n the nonliner reltions of G /G x versus γ n is provie to illustrte the iportne of onsiering stress rtio n oisture onition in the response spetru nlysis of groun

2 2 LABORATORY TSTS 2. Mterils The loose eposit teril obtine fro site of the Mino highwy lote in Minzhu, Sihun provine, is inly opose of liestone rubble n wethering prouts. Nturl ensity is.98 g/ 3 n oisture ontent is bout 3.0%. The site grtion of loose eposit is orse-grine teril onsisting of prtiles up to 600 in size. The prtile size of the in situ loose eposit is reue by the prllel grtion tehnique, with xiu prtile size of 60,the grin size istribution of sple re shown in Fig.. Fig.. Prtile size istribution of site teril n tests teril 2.2 Speien preprtion n testing proeure The tests were rrie out with lrge-sle yni trixil equipent TAJ-2000.The onfining pressure ws pplie by the ir-wter pressure syste, with xiu pressure of 5MP. The yli xil lo ws pplie by the oil hyruli syste, with xiu xil lo of 500kN. The speien size in 300 ieter n 600 in length. Two kins of sples, ir-rie n sturte, were prepre with the ontrolle ry ensity ρ =.90 g/ 3. After sturtion, the speien ws loe uner onfining pressure σ n stress rtio K (stress rtio K efine s the rtio of xil lo n onfining pressure n the ry ensity of speien before n fter onsolition ws given in Tble. Tble shows tht the ry ensity of se prepre speien fter onsolition is ifferent uner the se onfining pressure σ n vrious stress rtio K. In this se, the initil voi rtio of the se prepre sples woul be ifferent before yli stress loe. While the initil voi rtio hs signifint influene on sll strin yni sher oulus G x, it is not esy to istinguish the effets of voi rtio n stress rtio K on G x. The experientl results showe tht, in the onsiere rnges of onfining pressure n stress rtio, the ry ensities of the se prepre speien fter onsolition were well norlize with the en effetive stress σ (see Fig.2. The xiu yni sher oulus G x were lulte using σ n the influene of ifferent onsolition stresses on initil voi rtio were onsiere i.e. the ry ensity of se prepre sples fter onsolition ws unifie with the se en effetive stress σ. After onsolition, the yni xil lo in sine wve ws pplie step by step. very sple ws loe in 0 steps, eh level of lo yle 5 ties. The typil test urve ws shown in Fig.3. Tble.. Dry ensity of speiens before n fter onsolition σ (kp Initil ry ensity ρ i (g/ 3 Dry ensity fter onsolition ρ (g/ 3 K = K =2 K = ( Fig.2. Reltion of the ry ensity fter onsolition n the effetive stress Fig.3. Typil test urves: ( reltion urves of σ n yli ties; (b reltion urves of ε n yli ties (b 278

3 3 TSTS RSULTS 3. ffets of stress rtio n oisture onition on the xiu yni sher oulus G x The epiril forul for the sll strin sher oulus propose by Hrin is: x =A'p (σ /p n, where A' is the iensionless preter, p enotes the tospheri pressure, set s 00 kp, σ the en effetive prinipl stress. The reltionship between σ n ε n be expresse s hyperboli urve: = /(+bε. Fig. 4 n Fig. 5 showe tht the test t in / -ε plne n be well fitte s lines, where b is slope of the line n / x is the interept. In lg( x -lg (σ /p plne, x t ifferent K is not on the se line, s shown in Fig.6, whih illustrte tht the stress rtio K hs signifint effet on x n the Hrin s eqution y unerestite the influene of stress rtio K on x. In orer to lulte the effet of stress rtio on x, n iprove epiril reltion bse on Hrin s eqution is propose: ( n x A p ( / p ( K vrious stress rtios:(k =; (bk =2; (K =3 ( (b ( ( Fig.5. Reltion urves of / n ε uner ir-rie onition t vrious stress rtios:(k =; (bk =2; (K =3 (b The preters of the eqution ( n be obtine fro the fitting t of Fig. 6. Consiering γ =(+ν ε, G = /2(+ν, ν is yni Poisson's rtio of eposit soils, set ν =0.3, then G x =Ap (σ /p n (K, in whih A=A'/2(+ν. For two ifferent oisture onitions, preters re liste in tble 2. ( Fig.4. Reltion urves of / n ε uner sturte onition t Fig.6. Reltion urves of x /p n σ / p of loose eposits t 279

4 vrious onitions Tble.2. Preters of the epiril eqution Physil onitions A' A n Sturte onition Air-rie onition ffet of oisture onitions on G /G x To nlyze the influene of ifferent oisture onitions of eposit soils on G /G x, norlize sher strin γ n is use to norlize the G /G x -γ reltionships. Substitution of q. ( into the hyperboli forultion =/(+bε gives A p ( n / p ( K A b ( ( K / p n The norlize strin ε n is efine s follows: n n ( / p ( K -/2 Substituting q.(3 into q.(2 gives / 2 x A b ( K n (2 (3 (4 Converting the opression oulus n opression strin into sher oulus n sher strin using reltionships A=A'/2(+ν n γ n =(+ν ε n, the q.(4 n be expresse s: G G x k n where k=2abσ (K /2. As show in Fig.7, the preter k on sturtion onition is.7 n ir-rie onition is (5 Rollins' forultion with ifferene preters. The preters of ping rtio versus sher strin uner ifferent oisture onitions n be obtine fro the optil fitting urves expresse s Rollins' forultion, s show in q.(7 n q.(8. Sturte onition: D.2 7.9( 0.20 (7 (% n Air-rie onition: D(% ( 0.20 n 0.65 As shown in Fig. (8, the ping rtio of ir-rie onition loose eposit is slightly lrger thn tht of sturte onition n the effet of oisture onitions on D is not so signifint. It is worth noting tht t γ n <0-4, the test t points re generlly bove the fitting urves, the in reson of this phenoenon y be tht the frition use by the instruentl xil owel br ffete the test results. (.2 (8 Fig.8. Reltion urves of D n γ n uner ifferent oisture onitions:( sturte onition; (b ir-rie onition (b Fig.7. Norlize reltion urves of G /G x n γ n of loose eposits t vrious onitions 3.3 ffet of oisture onitions on D The test t of ping rtio D versus sher strin γ n is sttere thn tht of G/G x versus γ n. Aoring to Rollins(998, the reltion urve of D n γ of grvels n be expresse s: D 0.8 8( 0.5 (6 (% The test t of loose eposit n be esribe s the 4 APPLICATION To illustrte the influenes of stress rtio n oisture onition on seisi response nlysis of loose eposit, 60 lyere eposit oel is onsiere, s shown in Fig.9. The equivlent liner etho is use in the pplition (Zhng et l The lulting preters of eposit lyers oel re liste in Tble 3. Four situtions of the oel re onsiere: # without onsiering the ifferene of stress rtios (K =2, opting the previous wter level; 2 # onsiering the ifferene of stress rtios, opting the previous wter level; 3 # without onsiering the ifferene of stress rtios (K =2, opting the urrent 280

5 wter level; 4 # onsiering the ifferene of stress rtios, opting the urrent wter level. Fig.0 shows four response spetr of elertion for single egree of freeo struture (λ=5% t the groun surfe eterine using the input of the rok outrop otion n the generlize G /G x n D urves. The input of rok outrop otion is l Centro wve n the pek elertion is 0.34g. When onsiering the ifferene of wter levels,response spetr uner # n 3 # onitions re uniol n the # onition pek elertion is.08g, sller thn tht of.5g t the 3 # onition. When onsiering the ifferene of stress rtios, s 2 # n 4 # onitions, spetr re ultiol n the peks re.0~.5g t the 2 # onition n.5~.30g t the 4 # onition. These results illustrte tht the oisture onition n stress rtio hve signifint influenes on response spetr. Fig.9. Sketh of loose eposit lyers oel Fig.0. Spetrl elertion uner vries onitions Tble.3. Clulting preters of eposit lyers oel Lyer nuber Thikness / Dry unit weight kn/ 3 Totl unit weight kn/ 3 Stress rtio K CONCLUSIONS Bse on the lrge sle yni trixil test results, n epiril eqution onsiering the effet of stress rtio K bse on Hrin's forul hve been evelope, n the effets of oisture onitions of loose eposit on the reltions of G/G x -γ n D-γ were lulte. In ertin rnge (K =~3, the stress rtio is lrger, the G x is greter. Copring the two urves of the G /G x versus γ n, it ws foun tht the urve uner ir-rie onition ws ore nonliner thn in sturte onition. Moreover, the ping rtio uner ir-rie onition is slightly greter thn sturte onition. A se nlysis showe tht the stress rtio n oisture onition h signifint influenes on the response spetr of groun surfe, the stress rtio ffete the response spetr of elertion n the pek elertion in the sturte onition ws lrger thn tht in the ir-rie onition. Therefore, oisture onition n stress rtio nee to be onsiere when response spetr re selete for esign. ACKNOWLDGMNTS The finnil support of the Ntionl Nturl Siene Fountion of Chin(Grnt No n the Key Reserh Progr of the Chinese Aey of Sienes (Grnt No. KZZD-W-05 is knowlege. RFRNCS Chien L. K. n Oh Y. N. (2002: Influene of fines ontent n initil sher stress on yni properties of hyruli relie soil. Cnin Geotehnil Journl, 39(, Hrin, B. O. n Blk W. L. (966: Sn stiffness uner vrious trixil stresses. Journl of the Soil Mehnis n Fountions Division, ASC, 92(2, Hoque. n Ttsuok F. (2004: ffets of stress rtio on sll-strin stiffness uring trixil shering. Geotehnique, 54(7, Qin X. n Gry D. H. (993: Vois n grnuloettry: effets on sher oulus of unsturte sns. Journl of Geotehnil ngineering, ASC, 9(2, Rollins K. M., vns M. D., Diehl N. B., et l.(998: Sher Moulus n Dping Reltionships for Grvels. Journl of Geotehnil n Geoenvironentl ngineering, ASC, 24(5, Sully J. P. n Cpnell R. G. (995: vlution of in situ nisotropy fro rosshole n ownhole sher wve veloity esureents. Geotehnique, 45(2, Sun J. n Yun X. M. (2007 ffets of onsolition rtios of sns on yni sher oulus n response spetru of soil surfe. Rok n Soil Mehnis, 28(3, Vssllo R., Mnuso C, et l. (2007: ffets of net stress n sution history on the sll strin stiffness of opte lyey silt. Cnin Geotehnil Journl, 44(4, Wu S., Gry D. H. n Rihrt F.. (984: Cpillry effets on yni oulus of sns n silt. Journl of Geotehnil ngineering Division, ASC, 0(9, Yu P. n Rihrt F.. (984: Stress rtio effets on sher oulus of ry sns. Journl of Geotehnil ngineering Division, ASC, 0(3, Zhng J. F., Anrus R. D. n Jung C. H. (2005: Norlize sher oulus n teril ping rtio reltionships.journl of Geotehnil n Geoenvironentl ngineering, ASC, 3(4,