undrained behavior of sand.pdf

8/14/2019 Undrained behavior of sand.pdf

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561U NuvcllllJea'. I Hl1 6

.Iouruul of theSOIL f\IECIIANICS AND FOllNDATI00:S DIVISION

Prncl.'cdings of Ihe Americun SOCil.'ly of Civil Engilll'ers

UNDRAINED STIlENGTH CHARACTERISTICS OF COHESION LESS SOILS, By H. Balian Seed,' M. ASCE. and Kenneth L Lee,' A. M. ASC

- ' ,' IINTRODUCTION ,.:1

; I, ' .,;r In most practical cases where saturated couestontess soils are involved~ In slablllly problems, Ihe ra t e of applicallon of dl:Hur\)ing to r ces Is so slow". that any chauges In pore water pressure Induced by Ihe loads an' di ss ipated asu.e loading progresses. Thus the strength characteristics of lnt e reat a r e

Ihose developed under drained condtttona In the laboratory .In ca s es Where rapld loading occurs, however, even cohesion less soilsmay nol have time to drain during the loading process and the undrainedstrength must be determined. Such cases Involving one -directton loading mightInclude (t) the effects of btast loading on soli deposits, (2) Ihe effects In theluunedlat e epl ceut ral region of a small local ea rthquak e, for which groundaccel erations may ue very high but of very short duration, and (3) Ihe effectsIn very c lo s e proximity to me causallve fault of a strong eartnquakc.atthoug},Ihis may depend on t he r elattve position of the earlh srructure involved andIhe zone of fault displacement. Under more general ea rthquak e condlu ous,conestontess soils Illay he undrained during loading but tne sr r es s or sj r alna ppltcattons will ue cyclic In uatur e , C yclic loading effecls a re quite dlffcl'entf rom t hose In whl eh th e S\l 'ess o r strain Is Increased progress ively unlll failure occurs. Conventional sf r ength det er mlnattons are only made fur Ihis laller- unlll- .\prlli-:t9li8. To eXlendlllt: ; ; i ~ S I ~ 1 l II.I-;;-on" I l I u n l ~ \\ 1 111 1:1\ 1' '1ue SI must lie lII d \\1111 Ihe Lxceullvc S C rcl.r y, ,\SCE. This Ilap"r is pariof lhe copyrillhlcd Journul 01 Ihe Soli ,\Icehanlcs allil 1'0ulld"IIo>IIS 11I\'IslulI. I'rucccdlllilsul Ihe ,\ Il\ed e,," ~ d e l y 01 Civil 1I11l11l"crs. \'01. l3. :-: 0 . : ; u\'c," locr , I ~ I ; ~ l u I I I I -scripl wns sull,"IHc,1 for review for poasuue (lIIlIlIcall')1I UII ~ 1 1 I 1 1 lli" ,.c '"

I Prof. of Clv. ElIl(rll., IJnlv. of Cullfom ill. IIcl'kl:lcr. Calif. ,2 ,\Ssl. Pr of. of ElIl;rt:,. ('"Iv , of Calilurnla. Los ..IIIl I s. Calli.333

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~ ' I I I ' I U h I ' , 1!Jli7 (j"',lulllilJlI, .uul 1J1I. ,-dl ..'li,.II;1I load al'lllkalioll,; III thh trp. an ' Ih,' on lyl I I lH l i l i l l l l ( I I I1S ld l I ( d h('I ('iu .

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1'1l1::\'IOUS I:-\VESTIGATIO:-;S'.. '1, Sin.,(, lhe ( 'arlr d a ~ s i c a l expr-rjuu-ut s of n l ' r n o h l ~ , ' ougtnecrs have 1'1'1:01:' nlH'd that H I I ~ ~ a l l ~ 1"llrl III ,lilal" w l U : i i S i I . By filling a rubhur LJag

with llah1l'alo',1 ~ a l l l i and hell(ll'fol'lnlllj( II, Ir eynokts ueruonsu-nt ed ljualilallvl,l\, Ihal 1111


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: --.-\1X:: 336 Novcmue r , 1961 Ii su Ii UNDflAINI:;.D STlll::NGTll CIIARACTEllISTICS 331 ' 0. : t." cauutty ,If a slmpll(ied procedure (or pr edictlug, Irorn drained lest data , the;'( ;' undl'alned st r ength of saturated conestculess mat er la ls ,it

ClllTlCAI. VOID (lATlO A(';O ClllTiCAL CONFINING Pflt::5SUIlE .The )ctalh1nship between volume changes, void rauo anu confining pressure:H in drained lesls on a cohestontess matertal Is IlIuslrated In Fig , I, It a series

1/. of lIralned tests Is couduct ed , using a constant confining pressu re, on samples."1: halt CO '''''I' ' a , I , . ..11.4.. . . (0 .. . , ... S plooia ::. ." . CO , ,. 'tt . .... $ '1o AOIoO ,1 .'- ,. ,I . '1".1...,... 1! t --- :f1NING 1 1 I 1 : S ~ i 1 1 I 1 ~ : uy conducting similar series or tests at different values uf r' a s erieso correspoudtng values of critical conllnlng pressure and void i-auo, c couldhe determined. fig. I (d , from which the relationship between o,crll and rccould be estaultsneu all shown In Fig. I( /l.II (ollows (rom the definitions ol crtucal void rallo and critical confiningpressure that the r elauonsbtps shown in Figs . 1(1") and IU) are Identical in

Iorm. For example, It, (or rests couductedat a confining pressure nt 2 kg persq ern, the cdlical void ratio were found 10 be 0.1 Ihen II would necessarily011 ow thai (or tests conducted using a void rallo aller consolldalion /'c : 0.1 ,there would be no volume change alfallure only It the confining pressure wer e2 kg per sq em; that is, the criti cal confining pressure wouut be 2 kg per sqcm. Thus , (or samples prepared In the same manner, the relauonslup betweenthe crlli cal void rallo ecrU and the confining preasure under which samplesare initially consolidated o, c j s also the relationship between th e cr it lcat con

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Nuvr-ruhe r, 1 l()1 cfwinl( 1'1'I ',;sllrl' II . , . il alhlllH' vuid rut u)aft er eonsotutau uu umIe r Ih(' 1'1l1l1lnlUI(11I' 1';SUrl', I' , as shown in Frg. 2.

coxu r r roxs AT FAI l ,Um: II'> Ul\D1IAIi t::D TESTSIf It is as sunu-d Ihal IIIl' r elutroustup between crilical confining pres sure

ruut void rnt io Is 11


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November, 1061 SM 640pore water pr essu r e would drop. eventually reaching a value of about - I atm.At this stage the stress condltions woudl be those shown in Fig; 4(e). Furthe rdeviator st r ess applicallon beyond Ihls stage would cause ca vltatton of the porewater and failure would be approached wllh the effecllve contuung pressurer emalntng constant at the value o,ccll + I. Thus, 011 failure Ihe eff ect ive majorPr tnclpat st ress would be

0, / ' (o,cell + I) Ian" ( 45 t (I)Since the sample wonld In fact dilate when the po r e wate r pressure COlvitaled,Ihe app r op r late value of 0' In Ihls exp r esston would be simlla r to that det e r

10101 Sl ...... POll Wall. P'- ...... I [Ulu , ' ,51......\ I':.j \01 -(}-. [ ] -0

u. ::'bl nd au' U 6-.0 '1,,'1 0 ali-


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Nuvr-mher, 1!l61 uFit:, 5(d, II Illayhe 11011 11 ill Ihlslih'UI'e Ihal al Ihls 6 l a ~ c Ihe po,'c w.uer pressur' is st i l] ~ r p a l p r than -I '" - 0,,;.-11I. Since the re will he not in luw 11


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JH Novemher, I!lfi1 SM 6

TIH' stops involved In ullll:tlnf( Ihls approach are as follows:I. Eslahllsh Ih(' reiallonshilllwlwe('n uu- ('ffeclive cousulldat ron .presaur-e

0 . and ure voul rnrto atro r conscttdai ton "" as shown In fil:. 7(,/1. This r otartonshtp will depend on rhe Inillal void rallo oflhe samples. r j .

2. Estnnltsh, from drained 1('515, the r e lauoushlp belweeo void r at io OIlierconsullrlat lou and crillcal coofillilll: pressure as shown ill fif( o7( hI.

i': ~ . . IIL -- _ S< L , . .i

101

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II

/ /SIl ....P 8 .. I ,t. Q I I a i l l )

~ t l . 1. ,_.,lI t , . . . , . . , l I tI. ...., . ,. ' I I I p .... . COAI' I' P

tc IrH . 7 . - I l I ; H ~ I I : - : , \ T I ( ) : OF F .\ 1I.t:III-: C O ~ I J l T I O : ~ 1.\ C t I : - l ~ O l . l l L \ n : / I - U N / ) I l N t : / ) TESTS

J . for any value of the errecuve consolldallon pressure 0 . . det e rnune Ihecn r r cspoudiug value of the crutcat conllnl,i\(; pressure as shown in figs. 7 11)an\17(h). Hencc establtsh a r ~ l a l i o l l s h l p b e l w e e l l l h e crtttcat courtutng pressure3erll and the ettccuve consotluatton Ilrl'Ssure all as shown by Ihe line AD inFif(.7(d

1 . SlIpl'rilllpose on Ihe pial in flf(. 7( d. a line CD expres'sing Ihe rclallonshipOJ u'c t li t i 15)

UNDllAINEO STflENGTII CI/AHACTflJSTlCS 3'155. Dete ruuue Ihe point of lnre rs ccuon X of the Iwo re lat iuus hips shown In

Fif( . 7( r] . for cousottdat ton pressures less Ihan Ihal correspondinl: 10 point 'X, me effeclive conflnln\{ pressures at Callure will be these det e rmincd by Iheline ex . for consottdat tou pressures I:I'ealerlhan Ihal cor respondtng lu poinlX,lhe ettccnve confining pressures at Callure will be tnos o det e r nrinerl hy theline XD.

G. From a knowledge o rue eHeclive conflnlnl: pr-essures at Iai lure , a;dct er nune Ihe elleclive major principal stresses at CailureCrum the r e lat ionship

(I' . = , Ian-" -0' ) , . , (1611,/ 3/ 2usinl: an approprlate value of 0' . For samples which cavitate Ihe anf(le or I r lc lion should be one Inc ludlng some effects of dllallon but fur non-cavitatingsamples, an angle of frlcllon cor rcspondlng 10 constant volume condtt ionsshould be used .

COMPAflISON O f PrlEDICTED AND OBSERVED flESUL TSO f UNCONSOLIDATED-UNDflAINED TESTSON SATURA TED SANDS

T'est data conClrmlng, Ihe genera I Corm o Ihe r esulta Indlcaled In fig. 6 has111'1'0 pr esented by Bishop and Eldln .. .ll Penman. and Newland and Allely. ,uowever, no attempt has been made In previous studies 10 check the quanlltalive r etattonsntp bel ween lesl data Crom unconsoudatcd-undrmncn t esrs andr-esults predicled Cram values of the crillcal confining pressure det e rrulnedby drained lesls. Accordingly, series o drained and undr.uncd It;St5 were conducred 10 provtde data 10 check Ihis relationship.

The sand used Cor Ihese studl es was a Cine 10 medium, unllorm sand fromthe Sacramento Rier navtng void ratios at minimum and maximum densitiesof 1.03 and O.GI. r especttvely. Ihe results o several ser ies o druined restsperformed on Ihls sand have been reported by Lee and Seed. ' This reportalso contained a Iull d esc rtptton o Ihe sand charncrertsucs and the t esungtechniques. The undrained te5t samples were Iormed and t est ed Collowlng thesa III procedures.

The drained t est data which are perunent to Ihe pr-esent study are pr-esent I'dIn figs. 6 to 10. The retattonstup between Ihe void rallo aller consolldallonand the conClnlng pressure Car samples compacled Inllially 10 four 'tItHerenlvoid ratto condtttons Is shown In fig. 6; the relalionshlp bel ween the crllicalvoid rallo and Ihe crillcal conClnlng pressure determlned by drained tests isshown In FiK. 9; and the envelopes o Callure delermlned by tesls showing novolume change at Callure and by tesl data Cor drained 11 515 alter dilatancyetrecrs are deducted as proposed by Bishop and Rowe' are shown In Fig.10. At conllnlng pressures bel ween 5 and 30 kg per sq I'm . which coverS the

\ I.ee. K. 1... and Seed, II. n. " Drained Sirength Chuructcr lattca 01 CohcslonlessSolis," ~ o l \ ;\Iechunles and I\IIuI\\Ioou9 hlalerlals lIeseareh Luhor loq', ( n' crshy ofCIIHlorlll., Berkeley, Caill. JUlie. 1966.'ll\lshop. A, \1"" -Correspondence 00 Shear Sirellilth 01 n Salun'h,iJ :iHI In TriaxialCOilpressloo." Geotet: >"ltl".".. \'01. ;. 195;. flfI. 4 : l - ~ 5 Iluwe. p, I I ~ Illlutuncy lIelullon lor l l I l I e E'lulIllJrhln, uf all . - \ ~ s ~ l I l h l y ul Pn,C cles In Conlacl I r o c e e l I o g ~ lIoyal ~ o c l e t y Series ,\ . 1'01. 209. \leI.. I%2, (II ,[)1)0-521

7-- ---------- - - - - - - - - - - - - - - _ ~ I i i l .........,


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Novl'mht'I', 1961 S/l16 : - ; D I l A I ~ E n STIl ENGTIl CIIAIlACTEIlISTI C:i 341range 01 values 01c rit lca l confining pressure 101' this saud 101' samples varyingIrum lons e III ur -us e , Ih l' va riuus cuve lopes shown In Fig , 10 arc in r easonablyc los e ag rccruent . The te st data lor samples showlnl: no volume chalice al fallu re is so m ewhat uu ermed tate helween Ihe other Iwo curves and might there-101'1. he cons idc red 10 prov ide a reasonable value of Ihe angl e of fri cti on IIn(l"r. :..

... i, .. -. L .A...-o

1 _ _ _. - ......._1_ _ _........-

. u .. ,o n000

, 0 1

0 ',

060

0"

eonstant volume coun tuons. Fr om nu s envelope, lhe ang le of fr iclion underconstaut volume ccnu tu ons Is foullu 10 be c lose 10 :11 '.fr om th ese dat a, values of th e undrained st r engtn of lhc sanu may " ea,lily

hc p redtcr ed . Fur exampl e, Ihe predicted envelope of Iaiture lor 10lal st r es s esIor a s eries of uucousolluateu-uudratned t est s on sampl es of medium densesand Initially consotldated und er a confining pr essure of 3 kg per sq CIlI hishown in fig. II , The position of uus envelope was del e r mined a s foll ows .The Initial void ratto of thc m edium dense sand was 1 / 0 .11. from fig . 6,thc void ra u o after consotruauou under a confining IlI ' l ' SSlI l' C of :J kg per sq

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fAilI.IOP. '01 co".lollo' wolulfte cond,lton, 'h i .d b, ~ , 1 f t 9 flo 4ilotoAcrpUt t .A" 10 . . . . dolo '0' cit IlU'od

. apUU lon '0 IU ' da. Q '01 d4h .. .ond

'0

- - - - - - - - - - - - - - ,- - '

oO ou, , , fO - , .

f" lop. '0. co ,lool .alum. col\4lloon,l d.l mln,d 0, o p p a J I n ~ allhop 41k1.ont:,1"/(; . , - / I E / . . I T I / I . \ : i l l l l : ; 1I1: n nT . \ (;0.\1"/:\1:\(; I 'IlES:il'lll ' ,\ .\ 11 \"(111' 11.1 1 11, .\ FT EIi (;(l:,\SO/.lltlTIO '>" FOil" .1:\1' .\ T r / lnc 1. \ lrL\/. 111-: .\:;1 1 11 :"

(a p .nlgl . , . k)p. '0' Ino _ol ..tn ( gog. /I .0.-.. ..

t - .

, 0 l ) 0 0rl l ; . 11lI :-\\ I:1.0I El; OF " ' \11.1 1 11-: 11I:T1:IlMI\TII IIY I lIL\I .\ lln::>TS FOil(; O:\ST .\K T \ O l . l (;() .\JJlTIl I '>" l;. _-+ em may he s een 10be l r = 0.70 and from Fig. 9, the cl'lll cal connn tng pr es SUI'( , corresponding 10 this void rallo Is o,c rll ; 9.3 kg per sq em. Thus forthe constant volume angle o( friction, 0' ; 3'1", the eCCecllve major principalstress at failure In any noncavtt attng test, for which the e((ecllve milia" prino e - " . . -- - - - --t -

o . _ L .- - - ' : - - -L----- l . .- -- l-- - c ipal stress at failure will be equal 10 l l l may be determined Ir om Eq . -Io 10 1 20 10 to be : o i l ; 9.3 tall ' 45 + (3'11/2) ; 37.2 kg per s q cm. The cor rcspoudlngvalu e of Ihe deviator st ress a t failur e In noncavllatlng tests wlllbc oj,. - 0i j

3'/.2 - 9 .3 ; 21.9 kll pe s q Clll and Ihls condition will occur in alln (; , . - I l E / . \ / I I . \ S I I l I Il l : Til ' E E t\ CIII"I"Ie .\1. vou: unconsolidated-undrained tests conducted wllh an applied confining pr-essureIUTIII 1 .\11 C1unc \ . cl ) :\nt-.:It\G I'IiESSr/lE III:n :ll gre a te r Ihan o ,c"11 - I ; 6 ,3 kg per sq em , For tests conducted at confining~ 1 1 . \ F 1 1 F I l / l ~ 1 1111 .\1 .\ ' :11 TESTS p re s s u res less than this value, cavllallon will Occur befor e failure and theenve lope of failu re for total strcsaes wilithere(ore be parallel to Ihe d ratned

-, : strengu: envelope hUI ulspta ceu about I kg per s q ern 10 ui c lefl. Thus the'... '; . .


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34 Nm ( lIIh,r , 1061 SM 6co mplete ('I\vel"pl' nf Ia ilure In t e rms Ilf tuta l stressus, will be thai :;III ",'n in

II.Mnhr e i r c Ics 1 1' lolal s la'eSlies at Ia iture l r a number of uucousol idated

uudraiued Iests conducted on sa ruplcs pr epared and eousultdated as outl iuedahove are shown In fl/{. 12, for compa rison the pr-edicted envelope, shown infiR. II, is also plOIll 11 with lhe rest dara . The agr-eement between predict ed., . alld ('xllI'rinlcillal rcsulrs Is exeelleul. Slmllar agr eernent was ontatneu in

, . &. _ I1 ,. ,7 , . . _' - _ .,-_ .___ . -i I ;. ,1.l

... . .. .. " .j .j. .. -- .. - ._- " - - 0 0 --"-1

VII; , 1\ .-I-: :\\TI.I 111 ': lit FAIJ.llIE rou TllTAI. ; ; T l I 1:-; I I,Cll:-;SIlIlIJ,\TElIII?1. ;i j":::: ./; J. , . ;j ;

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n ::;"[:; 1'll ElJl CTEII t'1l11M I J l U I ~ I TEST 11:\1',\

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1, 11. . __. I . .. . 1. ..t .. II 1'\(; , C \ I I \ \ l I W (lllSEI\\ E11 I-'AII.I'III: CO:'\I'I"I'III:\S1:\ 1":\ ( '( 1:\: 11I.IIJ AT1:11-rx IlIUI :-;I:1l T ESTS

several oth er seri es ot i es ts condu cted on samples co mpacteu inilially 10 ouie rvoid ratios ,COMPARISON O f PREDICTED AND ODSERVED RESULTS OFCONSOl.IDATED-UNDRAINEO TESTS ON SATURATI::D SAND

lnvcsugaunns Similar 10 Ihal desc ribed above were conuucted 10 compa rc'Ihe strengths 01 s atura ted sampl es of sand In cou sotldat ed-undraiued leSlswilh tnose predtct ed Ir om a knowl edge nl Ihe cdll cal confining pre ssure s ,The pr-edi cted aurt measured positions 01 the total stress failure envelopes lora se r ies 01 C- U rest s Ilel'l orm ed "n Inlli ally loose sand ar e sh own In Fig. 13,

UNDHAI:-.IEO ST RENGTII CIlARACTERlSTICS H9The measured st r eugths are slightly higher Ihan Ihe pr edict ed strengths inth is case,Similar data (o r sea ies 01 C- U tests on Initially dense samples ol sand ares hown In fi g . 14. for the se samples the pr edict ed and measured str eugthsare In excellenl agreement.

Two oth er series '01 C-U leSIS were pertorrn ed on samples of the same. ..- .,_. _- ___ ..-- - _ .-_.._-..._. , , ..- _ . __ - 0 1).. _ ...._ ,...._. 0f3l "o.f:A

... II

_ _ 1- .... _--

FU . 1:l.-COMPAIlI:>OI..: OF OUS t: II\'1:0 ANO I ll t:IlICTEIl FAILCllt: E/\ \ E I.O I I:::>1/\ T I : : TESTS

t. .._ .. _ ................ _ 01 . 0 . _ 1 0 0__

.>-- ,- . .. -- .....

_......... ,.._. 8Ls .1

F U;. C O ~ I I , \ I I I S O O F onsuuv uu \ / \ l l l l t EIlI C THI "' .\11.1111 ': : : \ n < l I 11\ C (I:\ SOI.l Il,\T1:Il- lJ/\ IlIU INEIl T I - : saturated sand at intermediate densttf es. In eacn ortuese cas es Ihe measuredand predtcted positions 01 Ihe strength envelope were in close ag reernenr.Furthermore, t esrs were performed In each 01 the lour s eries 01 C -U test sat confining pressures to 140 kg per sq CIII. In all cas es Ihe measured andpr edlct ed st rength envelcpes continued as essenllally st raight Iioe extensions01 me envel opes shown In Figs . 13 and 14 and wilh good agre ement bel ween


10/14

- -.\ '. 350 Nnvemue r , l lli1 SI\I e(In'di clC'' and Ilhscrvcel st rengths t l l O U ~ O U lhe (ull rnng e '01' confining11I' ss ...:;.

CIlITIC A I. COl Fll\li G rn ESSUHE HIOM UNUnAIN ::U TESTSFig . I ShHW:; how Ihe crilical cOllfillillg pressu res (or a sand may he dcle:I'

nuu ed trnm onse rvaj ions 01 volume changes III a series or dr n iu ed t cs ts , IIIan analogous lashilln, values may atsu lie obtained (1'0111 ous ervat tons o( rneporc-wat cr pr es su r e changes In a series 01 uudralned tests . The changes inIhHc-wall'r 11I'I'ssuI'e at lallure obse rved I " Ihe undra lned tosts conduct ed onsamples having differenl denstti es and subJecled 10 dHrerenl conn ntng pressures a r e showlI In FIR. 15Ia). for te sts al any oue confiuing pressure, Ihevoid rat io (or which urcrc is no change In pore water pr essure at lalllll'e mayhe inle ,lI'l'l ed as the crlltcal void rnuo , Atr eruattvety, lor tests OIl allY Onevuirl ratio att er eonsultdation, the connuiug pressure lor which uier e Is nopore wat er IIIess'II 'e change at (allure may be considered 10 be the c rtti ca lctlnfining pres sure , Values of lh e criti cal confining pressure are 1II01'e easilydet e r minect if Ihe data III Fig. 15(II)are r eplou ed as shown III Fig. 15 h). Usingeither fil{. 15(11) 01' Fig. 15(1.1. II is Iws :;ihle ILl dl'll'rmine corublnnt tous 01cdlieal cOII(inlng Ilressure and crillcal voh1 1'01110 lor Ihe whole runge or poa sihll' elellsily cnndlt ions lor Ihls sand : Ihese results are shown In Fig . Iii.An a ltcru.u ive nu-thod or del ermlnlng values o( Ihecritlcal confining pressuro 11 001 undrained leSIS Is simply 10note Ihe e((ecllve minor ' p.-in cipal stressal lallnre In noncavltai ing rests , F'rom Ihe concepts preseiit ed earlier in lhepaper , this st r cs s should be equal 10 Ihe critical conllnlng pressure (or Ihepar t icula r dellsily coudulon of Ih e sample. Values of Ihe crilical confining11I'cssu re det er ml ned In Ihls way for all noucavitaung rest s pedor m ed on IheSac ra nu -uro HiveI' saud are shown In Fig . 17. 'l'h e r e.f s only a lillie s calier inIhe data which dettnes a curve similar 10 Ihal shown In fi g . 16.

A compa ri s uu o( Ihe rclat ioushlps between Ihe void rali o and rne c rt u ua]co nCl nlng pres sure del cr nuued or obs e rvattons or I I) volume changes in rtrniuedt cs ts ; (2) n( pore water prcssure changes In undrained tesrs ; and (3) uie eI f"c1ive min or (ldnclpal st r ess a t Iaiture In noncavilaling urul ratu ed t csts isSllllWn In 18. The retauoustnps are in close ag r eemeut ove r Ihe euti r e

r a n ~ of void ralios . The ~ r e a l e s l di s crepancy occurs In Ihe loose sand rang ewhere values of Ihe critIcal confinIng pres su re dcte rmln ed Ir om d ra iued restsare somewhat Smaller than those det ermlued from Ihe uud r ained tests. This

; -: disc r epnncy i s in accord with Ihe dlf(erence bel weenlhe ouserveu and predrct ed :' . value u( Ihe ulul raincel sll' englhs 01 loose sand samples shown In Fill:. 13.: :

. r VAI.UI:: S OF CIIITI C AI, CONFINING rnESSUm: FOn VAnIOW; It may hc seen from Ihe preceding results Ihal Ihe crili cal confining 11I'e s

Sll l ( Is a significanl chal'acled sllc delel'minlng Ihe lI,ulrained sl r ength


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, - , 6Nov('lllher, 1067 6 UNORAINED STRF:NGTII CIIARACTRISTICS 353

5..: . . . . . . . . . . . _ "-"'"'_ _',, _ ,0

o",t,.j I1 II

-- 'ii --

I'll. , 1,i,-IlI-:I X n l l \SIIII'S 111''1'\\1:1-:\ \'(1111II.\TlII \1' 1 1-:1\ ( '1I\SlIl l Il. \TlII\ ,\ : - I I C I l IT 1l' .\1. 1'11\1'1 \1\(; I'III:SS.. . II : 1 1 I : T 1 : I I ~ I I \ 1 - : 1 1 II\' I ' \ I I IUI \I-:II 'n.srs SII(I\\I\(; \1I1'1I1l1':1'1l1.SSI"Ill ': (,11,\ \1;(,: .\ T 1' \11... . 11: '-'l. _ .. 11,"\ ......... -.

i ,1L, ;

I :.. i .

' 11 ... . . . . ~ So... 1II1 I Q > ~ .. .."' . _ . . . . . .

H( . 1 . -III-:I..\'1'1I1 \SIIII' 111-: 1 \\,1 ':1-:\ v (II II1I.\TlII .\ I T F Il ClI \S ( l I I I l,\T 11I1\ ,\I,ll CIIITIt \( . ('1I\1 'I \1 \ ( ; PIII':SSl'IlI I I F T F I I ~ I I I \ F I I II\' I TFH :T n: ~ ( \ 1 l P I I I ~ C I I L \ I STIII':S,;\ 'I' 1".\ I I , I Il l: \ \ II C '\ v I T \ I' I x I;\ ' \1111,\1\1-:11 TE STS

by olher Invesllgator8.,Il->< III addttton, some further tests were performedall a limited number of other materials. The results of Ihese tnvesugauousa re summarized III Tallie I. Most oflhe values obtained from previous stuureswere delermlnect by drained tests. However values were obt ained from a lewunuralned tests for loose salls.

, . .. -. " ,-"'- - -., ...._ I....- ... .... \/ .. ~ ~ _ _ ..,. h, 'P" ,.,,, I;

""'"'-


12/14

i.c .,, 35-\

LII1 . . I . I I . I I I l f CIlITIl' II. I : - ; I ~ ( ; I'Ilt:SSllllt: FIlii 1' ,IIlIOI1SNov('nlhl' ', 1967 ~ t . 1 e SM Ii

Thus Ihe355NDnAI ':EO STIIENGTIt CItAnAC TEnlSTICS

maxlmum values 01 uio crtucat confining pressure Cor other den selal.l:\I'I.,11I .II.I TU IU Ui sands studied to date appear 10 be on lhe order of 151030 kg pel' sq em .

." ',1.10 " .1 " ..'1".. ... elllU ..1 ..,j11.11, U.. I : . l ln '." ":IIIlh .I1 ~ I . I I I ; / , . = Ik l . .I I ,Ilt-,., .""", ", " "111 , h,t i U ~ I I 1 I 1 '''' r 11':1',"... llu ll wI.r In -",,/l L 1 11"(' "11"''''0" SIGNlflCANCJ;: OF TItE INITIAL POnE wATEn pnEssunEON rue UNonAINED STnENGTII OF SANI.)1. .': 1,,, 1.1. r l... ...11,1 .. " ........ f . H . Ioi 1 ;&,Il j 0 , .. 10


13/14

-- ...Novelllhe r. 1961 SM 6356etfecllvl.' confining 11I'essu"e 011 any sample and Ihe deviator sr r eas at lailureloa' Ihal sample. On tne same figure a re shown Ihe values or ui e deviatorst ress es at lalhll'l ' ILII rest s courtuctcd wilh Ihe same etfecllve confillinc pressu res dnl"illg cllnsolioali on. bul wilh .. iffenlll values ollhe initial pore waterprr-ssure In tue samples c1urhlK Ihe consolidallon stage. The large illllul:nce01 rne (nilial pore water pr essure 011 Ihe undratned BIIellcl\. oCsalllpies Inwhich c a vr ta t iou occur's Is readily appa r enl ,Tues e results omphasf ze Ihe Imporlance, In tesuug saturat cd s auus , ot.cor r ect labor.uory r epreseutatton, not only 01 Ihe initi al effecllve stress

10 ~ ~ ~ ~ - - , - - ~ r ~ T ~60

,u, per Iq em ? .. ;:t...,.. '- ". 40

o

.

I'.3

.. 30UIl- ~ ~ p e Iqcm u I O ~ ~ P. q emcii 20oiiia 10

o o - - : - ~ - : : : ~ ~ 10 20 30InlliQIConlohdohon p, .nul t . " - kQPII aqeml c

ru ; IU. I : \F l .n: :O>CI: o r 1:\11''''1. 1'1IIII: - \ \ x n:Il I'IlESSl'IlI, 0 :\ ST IlE:" GT Il UFS ,\ : \ I l I:\ l 'l I :\ SlIl IIl . \TH. " :-'IIIl .\I :\I :l i T ESTs

couutuon on a soil etemenr, but also 01 Ihe Inilial pore water pressure In solielements which may be suhJecled 10 undrained loading condillons .

EFFECT O f OVERCONSOLIDATION ON CRITICALCON fINING PRESSURES

Due 10 Iluctuattons In gr ound waler level a granular soil may be over-consutldated at Ihe lime iI Is subjected 10 uudralned loading, wilh a r esultlng et IeI. I on the values ollhe crtucat conttnlug pressures delermlnlng Ihe undrainedslrclIglh. To tuvesugntc Ihls possihllily. a number 01 dense s amples 1 sandwere prepa r cd and tested In normally consotldated-undratned tests , Each 01Ihese samples had Ihe same Inilial volrt ratto, e j : 0.61. but uecaus e 01 Ihe

l l c n ~ i 1 l c a t l o n which ucc ur rert IllIrlnl( consctldut lou, Ihe void ratios, c' at Ihe:;Ial'l nf Ihe uuuralued test s were tess than the inllial vatue , In audlttou. other

-SM 6 UNOIl.AlNEO STIl.ENGTII CIIARACTEIl.JSTICS 351dense samples were prepared 10 Ihe same Inllial void ralio,l'j : 0 .61 andea ch ot thes e was consolldat ed under a couttntng pressure 1 40 kg per sq CIII.AI uus slage ttie conll nlng pressures on Ihe samples were reduced. each 10 adifCerenl value, and Ihe samples were allowed to rebound 10 an equttturiumcoudluon. The over - consoltuated samples were Ihen loaded 10 failure underundrained condtuous .

The st r engths oC both normally and over-consolldaled samples are plottedas a Cunction 01 the void rallo 011 Ihe end 01 consolldallon in Fig . 20. II maylie s een Ihal the data dellne a unique relallonshlp and for thls soil, Ihe uu

00. -- - - - - - - - . . . , - - ----.

'0

00t:Il '"Ifj 0ii1 0

e...o I . 0, .100I a.Q Holfn4lllJ' OA*Nld 0 .. ' - aftNl.lSQl.,

.0 i. ; ; I O ~ ~ ~ ~ ON 060 . n

VQt4 RGltO 1 5 w. Q I Jr4tfWMd ta .. . ,FIG. 20. - l : : r r I:: C T OVEIICONSOUn .\ TION 0:-: I lEI.ATI()NSIIIP BET\\lE ::N C U ~ I I'IIE:;51\,1': :>TIII::NGTII AND VOIIlIl TIO AT r l lUI l .1' NONCAVITATINGCONSOI.ID n :o-UNIIIlAIN1::11 TESTS

drained st r ength at any void rallo Is apparently Independent 01 whelher thesample Is normally or over-consolldaled.

ENVELOPE O f FAILURE IN TERMS OF EFfECTIVE STRESSESFOR UNDRAINED TE,STS AT CONSTANT VOLUMETo de l ermine Ihe undrained sf rength 1 a saturated sand in a noncavllallngt est II Is necessary 10 know Ihe angle of Irlctlon or envelope of lallure underconstant volume condilions. Several ways 01 delerminlng Ihls Ir oru drainedtest data have already been des cr tbedThe rest dala for noncavllallng undrained tests provides means ' deler

, - -


14/14

:l5U Novemhe r , 1967 SM 0mining (hc enve lope or (allure. In terms o( ettecttve st r esses, (01' constantvolume con.uuous.

T'est

undrained behavior of sand.pdf

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