Settlement characteristics of compacted clays after soaking

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1 Settlement characteristics of compacted clays after soaking Item Type text; Thesis-Reproduction (electronic) Authors El-Rousstom, Abdul Karim, Publisher The University of Arizona. Rights Copyright is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 25/06/ :20:18 Link to Item

2 SETTLEMENT CHARACTERISTICS OF COMPACTED CLAYS AFTER SOAKING Abdul Karim E1-Rousstom A T hesis Subm itted to th e F acu lty o f th e DEPARTMENT OF CIVIL ENGINEERING In P a r t i a l F u lfillm e n t o f th e Requirem ents For th e Degree o f MASTER OF SCIENCE In th e G raduate C ollege THE UNIVERSITY OF ARIZONA

3 STATEMENT BY AUTHOR This th e s is has been subm itted in p a r t i a l f u lf illm e n t o f r e quirem ents fo r an advanced degree a t The U n iv e rsity o f A rizona and is d e p o sited in th e U n iv e rsity L ib rary to be made a v a ila b le to borrow ers under ru le s o f th e L ib rary. B rie f q u o ta tio n s from th is th e s is are allow able w ithout sp e c ia l p erm issio n, provided th a t a ccura te acknowledgment o f source is made. R equests fo r perm issio n fo r extended q u o ta tio n from o r rep ro d u ctio n o f th is m anuscript in whole o r in p a rt may be g ran ted by th e head o f th e m ajor departm ent o r th e Dean o f th e G raduate C ollege when in h is ju d g ment th e proposed use o f th e m a te ria l is in th e in te r e s t s o f s c h o la r s h ip. In a l l o th e r in s ta n c e s, however, p erm ission must be o b tain ed from th e au th o r. SIGNED: APPROVAL BY THESIS DIRECTOR This th e s is has been approved on th e d a te shown below: /H. A. W ittan of. o f C iv il E ngineering

4 ACKNOWLEDGMENT The auth o r ex p resses h is a p p re c ia tio n to Dr. H. A. S u lta n, h is th e s is d ir e c to r, fo r th e c o n sid e ra b le tim e he sp en t in making very- c o n stru c tiv e c r itic is m in th e course o f d ire c tin g th is stu d y. This c o n trib u tio n was in v a lu a b le. A lso, th is work would n o t have been p o s sib le w ith o u t th e lo v e, encouragem ent, p a tie n c e and support from th e a u th o rs p a re n ts and grandp a re n ts. This I qannot ever ad eq u ately acknowledge.

5 TABLE OF CONTENTS LIST OF ILLUSTRATIONS v i LIST OF TABLES v i i ABSTRACT v i i i Page CHAPTER 1 - INTRODUCTION Scope CHAPTER 2 - EQUIPMENT AND MATERIAL Equipment M echanical Compactor (K neading Compactor - T e st Model No. C a lif. 90l-B» Ju ly 1963) S ta tic Compactor ( S o ilte s t Model AP-350 Vers o *Tes te r ) L everm atic C o n so lid atin g A pparatus M ate ria ls CHAPTER 3 - TEST PROCEDURES Param eters Sample P re p a ra tio n Compaction T est Procedures Kneading Compaction Procedure S ta tic Compaction Procedure C o n so lid atio n T est CHAPTER 4 - DATA ANALYSIS. 15 C o n so lid atio n v s. Square Root o f Time Curves Void R atio v s. P ressu re Curves C o e ffic ie n t o f C o n so lid atio n v s. P ressu re Curves.. 18 iv

6 V TABLE OF CONTENTS C ontinued Page CHAPTER 5 - DISCUSSION OF THE RESULTS E ffe c t o f Method o f Compaction on Magnitude o f S ettlem en t Comparison by S uperim posing Void R a tio s a t Low S tre s s Levels Comparison by Superim posing th e S a tu ra te d I n i t i a l Void R atios Comparison by Superim posing th e I n i t i a l Void R atio as Compacted E ffe c t o f Method o f Compaction on th e Rate o f S ettlem en t E ffe c t o f the W ater C ontent a t Compaction E ffe c t o f Method o f Compaction on the Compression Index E ffe c t o f M oisture C ontent a t Compaction on th e Compression Index E ffe c t o f Method o f Compaction on P re c o n so lid a tio n P ressu re CHAPTER 6 - CONCLUSIONS LIST OF ABBREVIATIONS REFERENCES

7 LIST OF ILLUSTRATIONS Figure Page 1. Kneading Compactor. A p p aratu s S ta tic Compactor A pparatus C onsolidom eter A pparatus P a r tic le - S iz e D is trib u tio n D eform ation v s. Square Root Time C o n so lid atio n T est R esu lts - W/C = 30.2% C o n so lid atio n T est R esu lts - (W/C).. = 24.4%, (W/C)s = 24.9% C o n so lid atio n T est R esu lts - (W/C)^ = 27.7%, (W/C) g 27. 9s C o n so lid atio n T est R esu lts - (W/C)K = 29.1%, (W/C)s % C o n so lid atio n T est R esu lts - (W/C)K = 30.4%, (W /C )g * ^ ' * C o n so lid atio n T est R esu lts - (W/C)^ = 32.2%, (ttf/c) g S e e e. e «. 0» 0 e.» e o e o C o n so lid atio n T est R esu lts - (W/C)^ = 33.7%, (W/C)g O O. O «e» O 6 6 « Compaction Curve Cc v s. yd f o r Samples Dry o f Optimum Cc v s. yd f o r Samples Wet o f Optimum W ater C ontent v s. Compression Index vi

8 LIST OF TABLES Table Page 1. C o n so lid atio n T est - Summary Sheet Comparison o f th e Magnitude o f C o n so lid atio n by Superim posing Low S tre s s Levels Comparison o f th e Magnitude o f C o n so lid atio n by Superim posing th e I n i t i a l S a tu ra te d Void R atios Comparison o f th e Magnitude o f C o n so lid atio n by Superim posing th e I n i t i a l Void R atio as Compacted Comparison o f th e P re c o n so lid a tio n S tre s s e s vii

9 ABSTRACT The e f f e c t o f two d if f e r e n t methods o f compaction on th e r a te and m agnitude o f s e ttle m e n t was in v e s tig a te d. These methods are th e kneading and th e s t a t i c com paction. S everal approaches are used fo r comparing se ttle m e n t m agnitudes due to th e method o f com paction. The e f f e c t o f th e i n i t i a l void r a t i o and th e molding w ater co n ten t on th e sw e llin g c h a r a c te r is tic s and consequently on th e m agnitude o f s e ttle m e n t a re s tu d ie d. Comparisons o f s e ttle m e n t b eh av io r o f samples compacted to th e same dry d e n sity by th e same method o f com paction b u t w ith d if f e r e n t w ater co n ten ts are made. The e f f e c t o f th e method o f com paction on th e r e s u ltin g sw e llin g p o te n tia l, com pression in d ex, r a te o f s e ttle m e n t and th e p re c o n so lid a tio n s tr e s s e s is o u tlin e d. viii

10 CHAPTER 1 INTRODUCTION Compaction i s a p ro cess which re a rra n g e s th e s o i l p a r tic le s in to a c lo s e r s t a t e o f c o n ta c t and thus makes th e s o i l more dense. This can be accom plished by tam ping, r o l l i n g, o r v ib ra tin g th e s o i l. This p ro cess w ill lead to an in c re a s e in d e n s ity, d ecrease th e p e rm e a b ility, and to a re d u c tio n in th e amount o f th e probable s e ttle m e n t. There a re fo u r w ell known methods o f com paction; namely, kneading, im pact, v ib r a t in g, and s t a t i c com paction. These d if f e r e n t com paction methods induce d if f e r e n t amounts o f sh ear s t r a i n r e s u ltin g in d if f e r e n t s tr u c tu r a l arrangem ents o f th e p a r tic le s and consequently d if f e r e n t p r o p e r tie s. In 1933, P ro c to r developed a la b o ra to ry t e s t fo r d eterm ining th e optimum w ater c o n te n t, o r th e amount o f w ater a t which a c e r ta in amount o f r o llin g o r tam ping w ill give th e h ig h e st amount o f com paction. Seed (1) and h is a s s o c ia te s found th a t th e molding w ater co n ten t and th e method o f com paction w ill a f f e c t th e s tr u c tu r e and consequently th e engin eerin g p ro p e rtie s o f compacted clay ey s o i l s. A g re a t d eal o f work and re se a rc h has been done in th e f i e l d o f com paction and i t s e f f e c ts on en g in eerin g p ro p e rtie s o f compacted s o i l s. Major c o n trib u tio n s are a ttr ib u te d to th e works o f Lambe ( 2,3 ), M itch ell (4 ), B olt (5 ), Low (6) and many o th e r s. 1

11 2 Any kind o f a s tr u c tu r e th a t i s to be b u i l t on a com pressible s o i l w ill cause th a t s o i l to s e t t l e.- The magnitude and r a te o f th is c o n so lid a tio n can be ev alu ated through a se ttle m e n t a n a ly s is. C onsolid atio n is a tim e-dependent pro cess during which a s a tu r a te d s o i l w ill d ecrease in volume under an a p p lie d lo ad. In s a tu r a te d s o ils c o n s o lid a tio n occurs due to flow o f w ater from th e s o i l under a hydrodynamic g ra d ie n t, th u s b rin g in g th e s o il g ra in s c lo s e r and causing a re d u c tio n in volume. The r a te o f th e outward flow o f w ater is dependent on th e p e rm e a b ility o f th e s o i l. In th e la b o ra to ry, th e ap p aratu s used fo r c o n so lid a tio n b e h av io r s tu d ie s is c a lle d th e co n so lid o m eter. C onsolida- m eters d i f f e r from each o th e r by t h e i r c a p a c ity and t h e i r mechanisms o f p re ssu re a p p lic a tio n. U sually loads are ap p lied in a g e o m etric ally in c re a sin g load p a tte r n, e. g., 1 /8, 1 /4, 1 /2, 1, 2, 4,... tons p e r square fo o t. Each load i s ap p lied u n t i l com plete deform ation i s accom plished. In cohesive s o ils each increm ent o f load is u s u a lly m ain tain ed f o r 24 hours o r more, w hile in co h esio n less s o ils, com plete d is s ip a tio n o f w ater p re ssu re occurs w ith in a few m inutes due to t h e i r h igh p e rm e a b ility. G en erally, specimens a re confined l a t e r a l l y in rin g s and th e r e f o r e, d u ring th e a p p lic a tio n o f an increm ent o f lo a d, d is p la c e ment read in g s are tak en a t d if f e r e n t tim e s, and a t th e end o f every in crem en t, th e void r a t i o is determ ined. The t e s t r e s u lts are u s u a lly p re se n te d in th e form o f d e fle c tio n v ersu s tim e and void r a t i o versus load c u rv e s. In 1954, Seed (7) and co-w orkers p u b lish ed a p ap er in which they d iscu ssed th e e f f e c t o f th e methods o f com paction on th e s t a b i l i t y and

12 sw ellin g c h a r a c te r is tic s o f s o i l. In an o th er pap er (1960) Seed, M itc h e ll, and Chan (1) d iscu ssed th e fundam ental fa c to rs a ffe c tin g th e s tre n g th o f compacted cohesive s o ils which in d ic a te d c le a r ly the in flu e n c e o f th e m olding w ater co n ten t and method o f com paction on s o i l - s tr u c tu r e. For samples p rep ared wet o f th e optimum m o istu re c o n te n t, and compacted by d if f e r e n t methods o f com paction, th e la r g e s t sh ear s t r a i n was induced by th e kneading com paction; th e s t a t i c compaction gave a l i t t l e sh e a r s t r a i n and th e im pact com paction f e l l in betw een, a ls e, a t high s t r a i n le v e ls, v a ria tio n s in th e method o f compaction d id not cause changes in th e sh ear s tre n g th. However, f o r sam ples p rep ared dry o f optimum, th e change in th e method o f com paction d id n o t produce any n o tic a b le change in co n siste n cy and sh e a r s tre n g th. In 1958, T. W. Lambe (2,3 ) p u b lish e d two p a p ers; one on th e s tr u c tu r e o f compacted clay s and th e o th e r on th e en g in eerin g b eh av io r o f compacted c la y s. In th e se papers he d iscu ssed th e r o le o f th e s o i l - w ater system on th e m echanical b e h av io r o f compacted c la y s. I t was a lso in d ic a te d th a t d if f e r e n t kinds o f s tr u c tu r e e x is t in compacted s o i l s, dry o f optimum i t is flo c c u la te d (random fa b ric ) and wet o f optimum i t is d isp e rse d (more o r ie n te d ). The o b je c tiv e o f t h i s th e s is is to study th e se ttle m e n t c h a r a c te r is tic s o f c lay s compacted by d if f e r e n t methods o f com paction. For th e purpose o f th is th e s i s, i t was decided to use only two kinds o f com paction: kneading com paction and s t a t i c com paction. The main

13 c h a r a c te r is tic s to be s tu d ie d are th e m agnitude and th e r a te o f s e t t l e ment. Comparison is made between two id e n tic a l samples having th e same w ater co n ten t and th e same dry d e n s ity, however, one o f th e se samples i s compacted in th e kneading com pactor and th e o th e r in th e s t a t i c com pactor. This t e s t i s done fo r s ix d if f e r e n t w ater c o n te n ts, w ith one o f them bein g in th e neighborhood o f th e optimum w a ter c o n te n t. Three samples a re on th e dry s id e o f th e com paction curve and th e o th e r rem aining th re e a re on th e wet s id e. Comparison o f th e e-logp curve fo r th e kneading compacted sample is made w ith e-logp curve o f th e s t a t i c sam ple, knowing th a t b o th sam ples i n i t i a l l y have th e same w ater co n ten t and dry d e n sity. This com parison p ro v id es d a ta re g a rd in g th e r e l a t i v e m agnitudes o f se ttle m e n t ex p erienced by each sam ple. A nother com parison is made betw een C^-logP curves fo r th e kneading com paction and th e s t a t i c com paction fo r th e id e n tic a l sam ples. These com parisons p ro v id e d a ta reg ard in g which sample has a h ig h e r r a te o f s e ttle m e n t.

14 CHAPTER 2 EQUIPMENT AND MATERIAL Equipment M echanical Compactor (Kneading Compactor - T e s t Method No. C a l i f. 901_B> j u ly 1963)! ~ : " This m echanical com pactor is a machine used fo r applying dynamic loads up to 2,000 lb s. Compaction in th e kneading com pactor as shown in F igure 1 is accom plished by applying a k n e a d in g -lik e p re ssu re to th e sample by means o f a tam per fo o t. The o i l and th e a i r p re ssu re w ill r e g u la te th e movement and th e load o f th e tam ping fo o t. The tamping fo o t has a cycle o f 2 seconds to r i s e and f a l l. I t a p p lie s th e a d ju ste d p re ssu re shown on th e d ia l over an a re a o f 3.2 square in c h e s, w hile th e r e s t o f th e sample is fre e to move. The load on th e tam per fo o t is c o n tro lle d by th e amount o f a i r p re ssu re a p p lie d in th e o il r e s e r v o ir. S ta tic Compactor ( S o ilte s t Model AP-350 V erso -T ester) This com pactor (F igure 2) is h y d ra u lic a lly o p erated and a p p lie s a load up to 30,000 lb s. in com pression. I t a lso can be used fo r te n sio n t e s t s. This machine is c o n tro lle d by a main power sw itch and a r e s e t sw itch. The d ir e c tio n c o n tro l can make th e machine go th re e ways: lo a d, n e u tr a l, and r e le a s e lo ad. and a loading r a te v a lv e. This m achine a lso has a load c o n tro l v alv e These v alv es a d ju s t th e r a te o f th e crosshead movement from 0 to 5 inches p e r m inute. Each v e r s o - te s te r is c a lib r a te d

15 6 Figure 1. Kneading Compactor Apparatus

16 7 Figure 2. Static Compactor Apparatus

17 w ith in 1 p e rc en t o f accuracy according to AASHO and ASTM s p e c if ic a tio n s. The proving rin g used to c a lib r a te th is machine i s made by th e U. S, Bureau o f S tandards C e r tif ie d Proving R ings. Leverm atic C o n so lid atin g A pparatus As shown in F igure 3, th is is a device used to c o n so lid a te a sample o f s o i l 2-1 /2 inches in d iam eter and up to 2 inches in h e ig h t. This is done by increm ents o f load in c re a s in g from 1/8 to 20 t o n s / s q.f t. This load is c a r rie d on a 20:1 le v e r system. The sample can be te s te d s a tu r a te d, o r a t i t s n a tu ra l m o isture c o n te n t. Upon load a p p lic a tio n, th e load is c a r rie d by th e w ater in th e p o re s. This w ater p re s su re is u s u a lly r e fe rre d to as th e h y d ro s ta tic excess p r e s s u r e. With tim e, th e w ater i s d rain ed from th e pores and th e load is tra n s m itte d to th e s o il g r a in s. This w ill lead to a d ecrease in th e volume o f th e sample which is c o n so lid a tio n. M a te ria ls The m a te ria l used in th e se experim ents is a commercial K a o lin ite - c lay (H ydrite 10, so ld by th e G eorgia K aolin Company). This is a w h ite, b r ig h t m a te ria l w ith a p a r t i c l e d iam eter o f 0.55 m icro n s. I t s p a r t i c l e s iz e d is tr ib u tio n is shown in Figure 4. I t is a lso found th a t th is m a te ria l has a high a f f i n i t y f o r o i l and w a ter. H y d rite 10 has a s p e c if ic g ra v ity o f 2.6 3, a liq u id lim it o f 62 p e rc e n t, a p l a s t i c lim it o f 35 p e rc e n t, and p l a s t i c i t y index o f 27 p e rc e n t. I t s n a tu ra l w ater co n ten t i s 0.46 p e rc e n t.

18 Figure 3. Consolidometer Apparatus

19 Percent finer by Weight Equivalent spherical diameter in microns. Figure 4 Particle - Size Distribution o

20 CHAPTER 3 TEST PROCEDURES Param eters There are two f a c to rs th a t e f f e c t 't h e com paction t e s t, dry d e n sity (yd) and w ater co n ten t (W/C). These two fa c to rs formed th e b a s is fo r s e le c tin g samples to be used in each t e s t. Five param eters a re u s u a lly in v olved in c o n so lid a tio n s tu d ie s. These param eters a re : C^ ( c o e f f ic ie n t o f c o n s o lid a tio n ), e (void r a t i o ), p (p ressu re a p p lie d ), C (com pression in d e x ), and p (g r e a te s t p re ssu re c P th e s o il was ever su b je c te d t o ). A ll o f th e se fa c to rs were determ ined as d e sc rib e d in T. W. Lambe's book (S o il T e stin g fo r E ngineers) (8 ). Sample P re p a ra tio n A c e r ta in amount o f k a o lin ite (h y d rite 10) w ith a 0.46 p e rc en t n a tu ra l w ater co n ten t is weighed on a 0.1 gram a ccura te b a la n c e. The amount o f d i s t i l l e d w ater to be added to th is sample to, accom plish a p a r tic u la r w ater co n ten t is computed and i s added to th e sample in in crem en ts. A fte r th e a d d itio n o f each in crem en t, th e sample is thoroughly mixed With th e w ater by rubbing between th e h ands. This o p e ra tio n ta k es approxim ately an hour o f m ixing fo r 2 kilogram s o f k a o lin ite. A fte r th e sample i s m ixed, th e m ixture is p laced in a p l a s t i c bag which is t i g h t l y s e a le d. This b ag, in tu r n, i s p laced in 11

21 12 an o th er bag, and ag ain s e a le d. p l a s t i c bag and se a le d t i g h t l y. A gain, th e sample is p laced in a th ir d A fte r t h i s, th e m ixture i s p laced in a humid room under a p l a s t i c cover where i t rem ains fo r 24 hours fo r tem pering. by w eight. A fte r th is tim e th e sample i s d iv id ed in to two equal p a rts One p a r t is compacted in th e kneading com pactor and th e o th e r is compacted in th e s t a t i c com pactor. Having th e same w eight and volume, b oth samples w ill th e re fo re have s im ila r dry d e n s itie s. Compaction T est Procedures Kneading Compaction P ro ced u re A fte r p la c in g th e 4 -inch d iam eter mold in th e mold h o ld e r, leav in g a c leara n c e o f 1/8 inch between th e b ase p la te o f th e mold h o ld e r and th e mold, a ru b b er d is c 3-15/16 inches in d iam eter and 1/8 inch in th ic k n e ss i s p laced on th e bottom o f th e mold. A pproxim ately 1,000 grams o f th e k a o U n ite -w a te r m ixture is p laced in th e fe e d e r which i s d iv id ed in to 16 p a r ts. The f i r s t p a r t i s th re e inches long and th e o th e rs are eq u ally d iv id e d. A fte r pushing th e f i r s t th re e inches in w ith th e p re ssu re in d ic a to r on th e low p re s su re 240 p s i, th e motor is s ta r te d to move th e tam ping f o o t, w hile th e mold and th e mold h o ld e r are r o ta tin g. The r e s t o f th e p repared m ixture is pushed in to th e mold in 16 increm en ts. A fte r a l l th e p rep ared m ixture i s in th e mold, 10 a d d itio n a l blows to le v e l th e sample are allow ed, th en th e tam ping fo o t -is r a is e d. A ru b b er d isc, i s th en p laced on to p o f th e sample and th e p re s su re le v e l i s in c re ase d to 350 p s i. The tam ping fo o t is lowered again and th e tim e r is s e t on 3-1 /2 m in u tes, which is e q u iv a le n t to 105 tam ps. A fte r th is tamping

22 13 tak es p la c e, th e m otor is stopped and th e specimen is trimmed in th e mold flu s h w ith th e upper s u rfa c e, and then weighed. An e q u iv alen t w eight o f m ixture is used fo r th e specimen in th e s t a t i c com pactor. Three 2-1/2 inch rin g s are pushed a t a very slow r a t e, in to th a t sample w hile i t is in th e mold, under a s t a t i c p re s s u re. The m iddle rin g is trimmed a t both s id e s, and s to re d in two p l a s t i c bags to be used fo r th e c o n so lid a tio n t e s t. P o rtio n s o f th e compacted sample were a ls o used to determ ine th e m olding w ater c o n te n t. S ta tic Compaction Procedure An equal w eight to th a t o f th e trimmed kneading-com pacted sample was p la ced in two la y e rs in a 4 -in ch d iam eter mold. Each la y e r is tamped w ith a s te e l rod 20 tim e s. Then th e sample is p laced in th e s t a t i c com pactor and com pressed u n t i l i t reaches th e same h e ig h t as th e trimmed kneading-com pacted sam ple. The s ta tic a lly -c o m p a c te d sample has th e same w eig h t, volume, w ater co n ten t and. consequently th e same dry d e n sity as th e kneading sam ple. The maximum s t a t i c p re s su re reached by th e com pressor was about 6,500 p s i. This load is k ep t c o n sta n t on th e sample fo r two m in u tes. Then th re e 2-1 /2 inch rin g s were pushed in th e mold to r e tr ie v e a c o n so lid a tio n specim en as d iscu ssed p re v io u sly fo r th e kneading-com pacted sam ple. From th e se two com paction t e s t s, we got two id e n tic a l samples having approxim ately th e same w ater co n ten t and dry d e n sity which were compacted by two d if f e r e n t m ethods. Compaction t e s t r e s u lts are shown on F igure 13 (see page 32) fo r samples compacted u sin g both the kneading iand s t a t i c com pactors.

23 Consolidation Test The two samples a re weighed to 0.1 grams and t h e i r h e ig h ts are measured using a one-inch gauge w ith a d ia l acc u ra te to th e n e a re s t in ch. The two specim ens are then p laced in two consolidom eters and s a tu r a te d w ith w ater fo r 24 h o u rs. P ressu re le v e ls o f 1 /4, 1 /2, 1, 2, 4, 8, and 16 t s f are a p p lie d co n se c u tiv ely each day on th e loading c y c le. On th e rebound c y c le, s tr e s s le v e ls o f 1/2 and 0 t s f are used. Readings fo r sw ell and s e ttle m e n t are taken a t th e fo llo w in g tim es a t each s tr e s s le v e l: 0, 1 /4, 1, 2-1 /4, 4, 6-1 /4, 9, 12-1 /4, 16, /4, 25, 85, 145, 265, 445, and 1,440 m inutes. At th e end o f th e unloading cycle th e samples are removed from th e co n so lid o m eters. These are then weighed and p u t in an oven o f 110 F to d ry. T h e ir f in a l w ater co n ten t a f t e r c o n so lid a tio n is determ ined. A fte r th is t e s t is com pleted, an o th er t e s t is done e x a c tly th e same way on samples o f d if f e r e n t w ater c o n ten ts and dry d e n s itie s.

24 CHAPTER 4 DATA ANALYSIS C o n so lid atio n vs. Square Root of,tim e Curves E ighty fo u r curves were p lo tte d fo r d ia l gauge read in g s versus th e square ro o t o f tim e fo r every load increm ent f o r both th e kneading and th e s t a t i c sam ples. From th e se graphs and follow ing th e procedure o u tlin e d in (Ref. 8) th e 100 p e rc en t prim ary c o n so lid a tio n, t^ ^ (tim e a t which 50 p e rc e n t o f th e c o n so lid a tio n took p la ce) and tg^ (tim e a t which 90 p e rc e n t o f c o n so lid a tio n took p la ce) are found. These r e s u lts are used to fin d th e void r a t i o (e) and th e c o e f f ic ie n t o f c o n so lid a tio n (c ). A sample o f th is graph is shown in F igure 5. The slo p e o f th e d o tte d lin e s is 1.15 th e slo p e o f th e s o lid continuous lin e, which w ill in te r s e c t th e curve a t th e p o in t corresponding to 90 p e rc e n t c o n so lid a tio n. Know the d e fle c tio n read in g a t 90 p e rc en t c o n so lid a tio n (d g g ), th e read in g a t which f u l l prim ary c o n so lid a tio n tak es p la c e ( ^ qq) can be e v alu a te d. The read in g a t which 50 p e rc e n t c o n so lid a tio n tak es p la c e may be computed as h a lf way between ds and d ^ g. The tim e corresponding to d50 can be read from th e curve ( t^ g ). Void R atio v s. P ressu re Curves From each lo ad in g increm ent th e v alu es o f d^gg (prim ary com pression), tg g, and tgg are ta b u la te d as shown in Table 1. The f in a l void r a t i o, (e) a t which e q u ilib riu m is reached is then computed as o u t lin e d in Table 1. A graph showing th e void v ersus th e c o n so lid a tio n 15

25 16 Pressure Increment from l/z4 to ^2 tsf Sample No 3 0 % K Elapsed YT in Win Compression Date Time Time (t ) in Mm. Dec : Dial in inches I Dec VT~ fitting Consolidation in Inches ( d_ = d50= 0, min. 586 sec. 135 sec. = Y T i n M min Figure 5 Deformation vs. Square Root Time 4 0

26 Table 1. Applied Pressure in Tons/sq.ft. Consolidation Test - Summary Sheet Final Dial Reading in in ches Dial Change in in c h es I Cum. Dial Change in in ches 2H from Dial Chongs in, 1 in ches Void Height 2H_2H0 in ches Void Ratio 2H-2Ho " 2H0 oe 1 Fitting Time I Coefficient of Consolidation (c j in seconds in lo"4 sq. cm/second H I H tgo 1 *50 O o.,4.a&l. L , ( I I I / o' 0,

27 18 t e s t p re ssu re i s p lo tte d fo r each o f th e 12 t e s t s. A sample o f th e se curves is shown in F igure 6. By th e use o f th e Casagrande method, p o in t 0 is th e p o in t w ith th e maximum c u rv a tu re. At p o in t 0, lin e OB is drawn tan g en t to th e curve and lin e OG is drawn h o r iz o n ta lly. The angle between th e se two lin e s is b is e c te d by lin e OD. The upward e x ten sio n o f th e la b o ra to ry v irg in curve in te r s e c ts th e b is e c to r a t p o in t A. From p o in t A a v e r tic a l lin e i s drawn downward in d ic a tin g th e Pp v a lu e, which is th e maximum p a s t p re ssu re th a t th e clay has been su b je c te d to. For each o f th e se 12 curves th e com pression index is found from th e fo llo w in g eq u atio n : C = e l " e2 c log p 2 - log Pi The p o in ts (e^, log p^) and ( e g,lo g p^j are two p o in ts on th e s tr a ig h t lower p o rtio n o f th e la b o ra to ry v ir g in curve. C o e ffic ie n t o f C o n so lid atio n v s. P ressu re Curves (Cyjgo ( c o e f f ic ie n t o f c o n so lid a tio n a t th e tim e when 50 p e rc en t o f th e c o n so lid a tio n tak es p la ce) and (Cv)gQ ( c o e f f ic ie n t o f conso lid atio n a t th e tim e when 90 p e rc e n t o f c o n so lid a tio n ta k es p la c e ) a re computed as o u tlin e d in Table 1. A p lo t o f th e se param eters v ersu s th e t e s t p re s su re i s shown o n -th e lower p a r t o f F igure 6. This p lo t show s th e c o n siste n cy o f th e Cv v alu es computed from u sin g e ith e r f ^ 0 o r t gg.

28 (Cv) in sq.cm/sec xio'4 Void Ratio (e) O Pressure in Tons /sq ft. Figure 6. Consolidation Test Results W/C = 30.2%

29 CHAPTER 5 DISCUSSION OF THE RESULTS E ffe c t o f Method o f Compaction on Magnitude o f S ettlem en t Comparison by Superim posing Void R atio s a t Low S tre s s Levels The c o n so lid a tio n (e-lo g P ) curves fo r th e kneading and s t a t i c sam ples having th e same d e n sity and w ater co n ten t were compared by superim posing th e void r a tio s a t low s tr e s s le v e ls as shown in F igures 7 through 12. Since- th e amount o f s e ttle m e n t is p ro p o rtio n a l to th e change in th e void r a t i o, th e r e f o r e, th e curve th a t has a s te e p e r slo p e i s re p re s e n ta tiv e o f h ig h e r s e ttle m e n t. The p ercen tag e d iffe re n c e in th e amount o f se ttle m e n t can be c a lc u la te d by th e use o f th e follo w in g form ula: p. o [5.A] where p = p ercen tage d iffe re n c e in m agnitude o f se ttle m e n t Ae = average change in th e void r a t i o between th e average 6 6 s t a t i c and kneading samples a t a l l s tr e s s le v e ls eq ss i n i t i a l void r a t i o o f s t a t i c sam ple. The r e s u lts a re shown in Table 2. - "* 20

30 21 ro fm Kneading Static <u o 4 o a: 4- O x d E q cr </> c m O By t n Kneading BY Kneading BYtonStatic Pressure in Tons/sq.ft. Figure 7. Consolidation Test Results (W/C)^ = 24 4 %, (W/C) =24.9% S

31 22 CO Kneading C\J Static o h By ta n Kneading ^ By t. Kneading DO By Static Pressure in Tons / sq.ft. Figure 8 Consolidation Test Results (W/C)K = 2 7.7%, (W/C) = % S

32 23 K) (\j Kneading Static <u o o tr fo ^ d g S X o <u E o O' O V) (M c i r O By tg0 Kneading A By t5q Kneading r? Z l By f90 Sfafic > O Pressure in Tons /sq. ft Figure 9. Consolidation Test Results (W/C)K = %, (W/C) = 28.9% S

33 24 CXJ Kneading Static a o m ro CM O By t -Kneading O- O A By t Kneading 50 # By tgq Static Pressure in Tons/ sq.ft Figure 10. Consolidation Test Results (W/C)K = 30.4 %, (W/C) = 30.2% S

34 25 Kneading Static T3 00 O By tg o Kneading A By t Kneading cr o u Pressure in Tons/sq.ft. Figure II. Consolidation Test Results (W/C)^ =32.2%, (W/C)s = 31.7 %

35 26 Kneading Static CM TJ ---k in By tan Kneading By t50 Kneading By t Static Pressure in Tons/sq.ft Figure 12 Consolidation Test Results (W/C)^ = 33 7 %, (W/C) =33.7% S

36 Table 2. Comparison o f th e Magnitude o f C o n so lid atio n by Superim posing Low S tre s s Levels Kneading Sample R e la tiv e Magnitude S ta tic Sample P ercen t D ifference (W/C) 24.4 Less (W/C) % (W/C) Less (W/C) % (W/C) 29.1 Less (W/C) % (W/C) 30.4 More (W/C) % (W/C) 32.2 More (W/C) % (W/C) More (W/C) % 27 The r e s u lts shown in F igures 7 through 12 and Table 2, in d ic a te th a t a g r e a te r se ttle m e n t w ill develop by u sin g th e s t a t i c compaction method a t w ater c o n ten ts on th e dry s id e o f th e com paction curve. On th e o th e r hand a g r e a te r se ttle m e n t w ill develop by u sin g th e kneading com pactor a t w ater c o n ten ts on th e wet s id e o f th e com paction curve. The p ercen tag e in c re a s e o r d ecrease in s e ttle m e n t i s r e l a t i v e l y sm all between th e two m ethods. The average d iffe re n c e ranges between 0.87 p e rc en t and 2.01 p e rc e n t o f th e th ic k n e ss o f th e com pressible la y e r. However, maximum d iffe re n c e could amount to approxim ately 6 p e rc en t o f th e la y e r th ic k n e ss which may s ig n if ic a n tly a f f e c t th e s t a b i l i t y o f th e compacted s o i l. Comparison by Superim posing th e S a tu ra te d I n i t i a l Void R atios The c o n so lid a tio n (e-logp ) curves fo r both th e kneading and s t a t i c samples having th e same dry d e n sity and w a ter co n ten t were compared by superim posing t h e i r i n i t i a l s a tu r a te d void r a t i o s.

37 28 The p ercen tage d iffe re n c e in th e amount o f s e ttle m e n t was computed u sing Equation [5.A] o u tlin e d p re v io u s ly, th e r e s u lts are shown in Table 3. The r e s u lts as shown in Table 3 in d ic a te th a t dry o f optimum, th e kneading samples w ill g e n e ra lly undergo le s s s e ttle m e n t compared to th e s t a t i c sam ples. However, wet o f optimum, th e kneading samples w ill experience more se ttle m e n t than th e s t a t i c sam ples. As shown in Table 3, th e d iffe re n c e s a re r e la tiv e ly h ig h e r than th o se o u tlin e d by th e prev io u s method o f com parison. This can be a ttr ib u te d to th e h ig h e r sw ellin g p o te n tia l o f samples compacted s t a t i c a l l y a t th e dry sid e o f optimum. Upon lo a d in g, th e excess w ater absorbed d u ring sw e llin g w ill be squeezed o u t, r e s u ltin g in more s e ttle m e n t fo r th e s t a t i c sample th an th e kneading sam ple. Comparison by Superim posing th e I n i t i a l Void R a tio s as Compacted The c o n so lid a tio n (e-logp ) curves fo r th e kneading and s t a t i c samples a t th e same dry d e n sity and w ater co n ten t were a lso compared by superim posing t h e i r i n i t i a l void r a tio s a f t e r com paction. The d iffe re n c e s in th e m agnitude o f s e ttle m e n t were a lso c a lc u la te d u sin g Equation [5.A], and th e r e s u lts a re shown in Table 4. The r e s u lts as shown in Table 4 in d ic a te th a t dry o f optimum, th e kneading samples w ill g e n e ra lly undergo le ss s e ttle m e n t compared to th e s t a t i c sam ples. On th e o th e r hand, wet o f optimum, th e re v e rse is t r u e From th e se th re e com parisons i t can be concluded th a t th e kneading com paction w ill give a h ig h e r se ttle m e n t on th e wet sid e o f optimum w hile th e s t a t i c com paction w ill give a h ig h e r s e ttle m e n t on th e dry s id e o f optimum w ater c o n ten t.

38 Table 3. Comparison of the Magnitude of Consolidation by Superimposing the Initial Saturated Void Ratios T est P ressu re Kneading R elativ e S ta tic P ercen t T est P ressu re R elativ e - P ercent Range t s f Sample Magnitude Sample D ifference Range t s f Magnitude D ifference 0-16 (W/C) 24.4 Less (W/C) % (W/C) 27.7 More (W/C) /42% / Less 1.27% 0-16 (W/C) 29.1 Less (W/C) % 0-16 (W/C) 30.4 Less (W/C) % (W/C) 32.2 Less (W/C) % More 1.25% 0-16 (W/C) 33.7 More (W/C) %

39 Table 4. Comparison of the Magnitude of Consolidation by Superimposing the Initial Void Ratio as Compacted. T est P ressu re Kneading R elativ e S ta tic P ercent T est P ressu re R elativ e Percent Range t s f Sample M agnitude Sample D iffe re n c e Range t s f Magnitude D iffere n c e (W/C) 24.4 More (W/C) % Less 0.81% (W/C) 27.7 Equal (W/C) % Less 1.55% 0-16 (W/C) 28.9 Less (W/C) % (W/C) 30.2 Less (W/C) % More 0.61% (W/C) 32.2 Less (W/C) % More 1.14% (W/C) 33.7 Equal (W/C) % More 0.97%

40 31 E ffe c t o f Method o f Compaction on the Rate o f S ettlem ent v t w here: C v T H = c o e f f ic ie n t o f c o n so lid a tio n «tim e f a c to r = lo n g est drain ag e p ath o f w ater flow t = elap sed tim e. Since i s in v e rs e ly p ro p o rtio n a l to th e tim e o f c o n so lid a tio n, th e re fo re, i t is d ir e c tly p ro p o rtio n a l to th e r a te o f s e ttle m e n t. A com parison o f th e r a te o f s e ttle m e n t can be done by a comparison o f the Cy fo r both kneading and s t a t i c sam ples under th e same w ater co n ten t and dry d e n sity. The low er p a rts o f F igures 7 through 12 show th e versu s t e s t p re ssu re curves fo r both the sam ples. From th e se superim posed curves no d e f in ite co n clu sio n reg ard in g th e e f f e c t o f th e method o f com paction on the r a te o f settle m e n t could be o u tlin e d. However, in g eneral i t appears th a t sam ples compacted by kneading w ill undergo s e ttle m e n t a t slow er r a te s than the s ta tic - s a m p le s. E ffe c t o f th e W ater C ontent a t Compaction On th e com paction curve (F ig u re 13) sam ples compacted dry o f optimum a t w ater co n ten t o f 29 p e rc e n t and samples compacted wet o f optimum a t w ater co n ten t o f 33.7 p e rc e n t have approxim ately th e same dry d e n s ity. Thus i t i s o f i n t e r e s t to compare th e e n g in eerin g b eh av io r o f th e se samples to r e f l e c t th e e f f e c t o f com paction a t w ater conten ts

41 O Kneading 100 # Static Density in Ibs./cu.ft Molding Moisture Content in % Figure 13. Com paction Curve

42 dry o r wet o f optimum in a d d itio n to th e e f f e c t o f method o f com paction. At W/C = 29% the i n i t i a l void r a t i o o f the s t a t i c sample is 33 s u b s ta n tia lly h ig h e r than the kneading sam ple, (1.46 v s ). On th e o th e r hand a t W/C = 33.7% the i n i t i a l void r a tio fo r the s t a t i c and the kneading samples are equal. At W/C = 29% the s t a t i c sample experienced more sw e llin g, upon s a tu r a tio n, than th e kneading sample (7.9% v s. 2.6%). On th e o th e r hand, a t W/C = 33.7% the kneading sample sw elled more than th e s t a t i c sample upon s a tu r a tio n, (4.4% vs. 2.23%). Comparing th e c o n so lid a tio n (e-logp ) curves fo r the s t a t i c samples at W/C = 29% and W/C = 33.7% by superimposing the curves at the void ratios under low stress indicates that the sample compacted dry of optimum w ill undergo more settle m e n t than th a t compacted wet o f optimum. The average d iffe re n c e amounts to 3.26 p e rc e n t o f the th ic k n e ss o f the com pressible la y e r. The consolidation (e-logp) curves for the kneading samples at W/C = 29% and W/C = 33.7% are compared by superimposing the curves at the void ratios under low stress. This indicates that the sample compacted dry of optimum will experience slightly less settlement up to a stress of about 2 tsf, and will undergo more settlement at stress levels greater than 2 tsf, than the sample compacted wet of optimum. E f fe c t o f Method o f Compaction on th e Compression Index F igures 14 and 15 show the re la tio n s h ip between th e compacted dry d e n sity and the com pression index (C^). F igure 14 shows th is r e la tio n sh ip fo r samples compacted dry o f optimum, w hile Figure 15 is p lo tte d

43 34 K Vd Cc s Xd Cc Compression Index Compression Index 0.30 e O 020 _ Dry Density ( yd ) Figure 14. Cc vs yd for S am p les Dry of Optimum O Kneading S ta tic o o O Dry Density (yd) Figure 15. Cc vs. yd for Sam ples Wet of Optimum.

44 fo r samples compacted wet o f optimum. The r e s u lts in d ic a te th a t a t s im ila r dry d e n s itie s th e com pression index fo r sam ples compacted dry o f optimum is h ig h e r fo r th e s t a t i c sam ples than fo r th e kneading sam ples. On th e o th e r hand, f o r samples compacted wet o f optimum, th e re v e rse is tru e. These r e s u lts s u b s ta n tia te th o se o b tain ed p re v io u sly. E ffe c t o f M oisture C ontent a t Compaction on th e Compression Index Figure 16 shows th e r e la tio n s h ip o f th e com pression index (C ) c versus the molding w ater co n ten t fo r both th e kneading and th e s t a t i c com paction. This r e la tio n s h ip in d ic a te s a g en eral tre n d o f a decrease in Cc - v alu es w ith th e in c re a s e in molding w ater c o n te n ts. This may be a ttr ib u te d to th e h ig h e r sw e llin g p o te n tia l o f sam ples compacted a t low w ater conten ts and the r e s u ltin g s o fte n in g o f th e s o il m atrix due to the absorbed w a ter. E ffe c t o f Method o f Compaction on P re c o n so lid a tio n P ressu re Table 5 shows th e v alu es o f th e p re c o n so lid a tio n p re ssu re (P^) f o r b oth th e s t a t i c and kneading samples a t v ario u s w ater c o n te n ts. The r e s u lts in d ic a te no s ig n if ic a n t change in th e - valu es due to the method o f com paction. This may be a ttr ib u te d to th e d e s tru c tio n o f th e n a tu ra l clay s tr u c tu r e d u ring com paction, th e re fo re d e stro y in g the s tr e s s h is to r y o f th e c la y.

45 w / c K c c s W/C cc O O o o Compression Index 0.2 O Kneading o # S tatic Molding % Water Content Figure 16. Water Content vs. Compression Index

46 37 Table 5 Comparison o f th e P re c o n so lid a tio n S tre s s e s Kneading S ta t i c W/C Pp, t s f W/C pp, t s f

47 CHAPTER 6 CONCLUSIONS This re searc h was conducted w ith the o b je c tiv e o f determ ining th e e f f e c t o f th e method o f com paction on the magnitude and th e r a te o f s e ttle m e n t. The fo llo w in g co n clu sio n s were found: 1. Dry o f optimum, clays compacted u sin g s t a t i c compaction w ill undergo more s e ttle m e n t than those compacted by, kneading com paction. 2. Wet o f optimum, clays compacted by kneading com paction experien ce more se ttle m e n t than th o se compacted by s t a t i c com paction. 3. No d e f in ite co n clu sio n re g a rd in g th e e f f e c t o f th e method o f com paction on th e r a te o f s e ttle m e n t can be made, based on th e r e s u lts o f th is experim ent. In g en eral th e kneading sam ples w ill undergo se ttle m e n t a t slow er ra te s than th e s t a t i c sam ples. 4. When compacted dry o f optimum, th e samples compacted s t a t i c a l l y w ill have h ig h e r void r a tio s than th e kneading sam ples When compacted wet of optimum, th e void r a tio s fo r both th e kneading and th e s t a t i c samples were e s s e n tia lly e q u a l. 6. Dry o f optimum, th e s t a t i c samples sw ell more than the kneading sam ples. The o p p o site may be tru e when compacted wet o f optimum.

48 39 7. For the s t a t i c a l l y compacted c la y, samples compacted dry o f optimum w ill s e t t l e more th an sam ples compacted wet o f optimum. S im ila r b eh av io r occurs fo r th e kneading samples when s tr e s s e d beyond 2 t s f. 8. Dry o f optimum, samples compacted w ith th e kneading compaction have low er com pression in d ic e s than those compacted s t a t i c a l l y. The re v e rse is tru e when compacted wet o f optimum. 9. Samples compacted a t low molding w ater co n ten ts w ill undergo h ig h e r s e ttle m e n ts, a f t e r soaking, than those compacted a t high w ater c o n te n ts. Compression index fo r samples compacted dry o f optimum i s h ig h e r than sam ples compacted wet o f optimum. 10. The compaction pro cess d e stro y s the s tr e s s h is to r y o f compacted c la y s, thus th e method o f compaction does not a f f e c t th e computed v a lu e s.

49 LIST OF ABBREVIATIONS com pression index; slo p e o f e-logp curve c o e f f ic ie n t o f c o n so lid a tio n void r a t i o ; volume o f voids/volum e o f s o lid s i n i t i a l void r a t i o a f t e r compaction void r a t i o a f t e r s a tu r a tio n p re ssu re in t s f p re c o n so lid a tio n p re ssu re in t s f w ater co n ten t in p e rc e n t; w eight o f w ater/w eig h t o f s o lid s dry d e n sity in p c f

50 REFERENCES 1. Seed, H. B., M itc h e ll, J. K., and Chan, C. K., "The S tren g th o f Compacted Cohesive S o ils ", ASCE Research Conference on th e Shear S tren g th o f Cohesive S o ils, U n iv e rsity o f C olorado, D enver, C olorado, June 13-17, Lambe, T.,W., "The S tru c tu re o f Compacted C lays", Jo u rn a l o f th e S o il Mechanics and Foundation D iv isio n, P roceedings ASCE, May, , "The E ngineering B ehavior o f Compacted C lay", Jo u rn a l o f th e S o il Mechanics and Foundation D iv isio n, P roceedings ASCE, May M itc h e ll, J. K., "The Im portance o f S tru c tu re to th e E ngineering B ehavior o f C lay", SC.D T h esis, MIT, B o lt, G. H., "P hysical-c hem ical A nalysis o f th e C o m p re ssib ility o f Pure C lay", G eological T echnique, Vol. 6, No. 2, pg , Ju n e, Low, P. F., "Movement and E q u ilib riu m o f W ater in S o il Systems as A ffected by S o il W ater F o rces", HRB M eeting, Jan u ary, Seed, H. B., Lundgren, R., and Chan, C. K., "The E ffe c t o f Compaction Methods on th e S t a b i l i t y and Sw ell P ressu re C h a r a c te ris tic s o f S o il", HRB, Lambe, T. W., S o il T estin g fo r E n g in eers, John Wiley and Sons, I n c., New York,