Effect of confining pressure on peformance of geotextiles in soils

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1 Effect of confining pressure on peformance of geotextiles in soils Item type Authors Publisher Rights text; Thesis-Reproduction (electronic) El-Fermaoui, Ali Ismail The University of Arizona. 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. Downloaded 5-Mar :22:09 Link to item

2 EFFECT OF CONFINING PRESSURE ON PERFORMANCE OF GEOTEXTILES IN SOILS By A ll Ism ail El-Ferm aoui A Thesis Submitted to the Faculty o f the DEPARTMENT OF C IVIL ENGINEERING AND ENGINEERING MECHANICS V In P a rtia l F u lfillm e n t o f the Requirements For th e Degree o f MASTER OF SCIENCE WITH A MAJOR IN C IV IL ENGINEERING In the Graduate College THE UNIVERSITY OF ARIZONA

3 STATEMENT BY AUTHOR This thesis has been submitted in p a rtia l fu lfillm e n t o f requirements fo r an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules o f the Library. B rief quotations from th is thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests fo r permission fo r extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean o f the Graduate College when in his judgment the proposed use of the material is in the interests of scholarship. In a ll other instances, however, permission must be obtained from the author. SIGNED: T APPROVAL BY THESIS DIRECTOR This thesis has been approved on the date shown below: c(aar LA>JL y EDWARD A. NQWATZKI ^ Associate Professor of C iv il Engineering and Engineering Mechanics r w _

4 ACKNOWLEDGMENTS I would lik e to express my sincere appreciatio n to my a d v is o r. Associate Professor Edward A. Now atzki, fo r his valuable assistance throughout th is study. I would lik e to thank him fo r providing me w ith great h elp, generous tim e and e f f o r t, and constru c tive c r itic is m. I am thankful also to the Dean o f the Engineering C o lleg e, Richard H. G allag h e r, and to Professor Hassan A. Sultan fo r review ing the manuscript o f^ th is th e s is. I give special thanks to Professor and Department Head o f C iv il Engineering, Paul H. King, fo r awarding me a h a lf-tim e teaching a s s is - ta n ts h ip fo r the M a te ria ls Lab during my graduate work. L a s t, but not le a s t, I wish to express my sincere appreciatio n to my dear L is a, to my brothers and s is te r s, and to my parents fo r t h e ir p a tie n c e, support and encouragement throughout t h is study program.

5 TABLE OF CONTENTS Page LIST OF ILLUSTRATIONS... LIST OF TABLES ABSTRACT vi x xi CHAPTER 1. INTRODUCTION... 1 O bjective and Scope o f the W o r k REVIEW OF LITERATURE General Review G e o te x tile C la s s ific a tio n G e o te x tile Polymers G e o te x tile T en sile Strength Experiments o f S oil Reinforcement w ith G eo textiles.. 19 Testing Equipment Testing Procedure G raphical R epresentation o f S o il-g e o te x tile Kinematics In te rp re ta tio n o f P u ll-o u t Test Results Test Results w ith Cohesionless S o ils PROPERTIES OF MATERIALS USED IN THIS RESEARCH G e o t e x t i l e s Sand and G r a v e l TESTING EQUIPMENT AND PROCEDURE Testing Equipment D ire c t Shear Device Sample B o x G e o te x tile Specimen Testing Procedure... 40

6 V TABLE OF CONTENTS C o ntinue d 5. PRESENTATION AND DISCUSSION OF TEST R E S U LTS Woven G e o t e x t i l e s P o ly f ilt e r X E ffe c t o f Dry Sand-Dry Sand In te rfa c e (S-S) E ffe c t o f M oisture Content E ffe c t o f Sand-Gravel In te rfa c e (S-G) E ffe c t o f G ravel-g ravel In te rfa c e (G-G) Comparison Between Various Combinations o f G e o te x tile In te rfa c e M a te ria ls and P o ly f ilt e r X M ir a fi 100X and M ira fi X Nonwoven G eo te x tile s M ir a fi S E ffe c t o f Dry Sand-Dry Sand In te rfa c e (S-S). 69 E ffe c t o f M oisture Content E ffe c t o f Sand-Gravel In te rfa c e (S-G) E ffe c t o f G ravel-g ravel In te rfa c e (G-G) Comparison Between Various Combinations o f G e o te x tile In te rfa c e M a te ria ls and M ira fi Typar 3601 and Bidim C SUMMARY, CONCLUSIONS AND RECOMMENDATIONS Page S u m m a ry C o n c lu s io n s Recom m endations REFERENCES 88

7 LIST OF ILLUSTRATIONS F ig u re Page 1.1 Reinforced earth a p p lic a tio n s French drain protected w ith g e o te x tile Conventional trench drain constructed w ith a d u a l-la yered aggregate f i l t e r and a drain pipe in fin e -g ra in e d s o ils Blanket drain constructed w ith g e o te x tile Embankment s ta b iliz a tio n -e ro s io n control Summary o f te s tin g program Shear box fo r p u ll-o u t te s ts P u ll-o u t te s t a p p a r a t u s D e tailed view o f the p u ll-o u t te s t apparatus S o il-g e o te x tile kinem atics associated w ith progressive f a ilu r e in a p u ll-o u t te s t Curves tu- +. versus a fo r id e n tic a l cover and support m a t e r ia l Curve ( t. + TgS) u-jt versus o in which one o f the m a te ria ls in contact w ith the g e o te x tile is cohesionless and the other one is fr ic tio n le s s Woven g e o t e x t i l e s Nonwoven g e o t e x t ile s Grain s ize d is trib u tio n curve fo r gravel D ire c t shear d e v i c e Sample b o x G e o te x tile specimen vi

8 vii LIST OF ILLUSTRATIONS C o ntinue d F igure Page 5.1 Specimen w idth versus h o riz o n ta l deform ation fo r g e o te x tile s studied (unconfined loading) H o rizontal forces and in te rfa c e shear stresses actin g on g e o te x tile specimen S tre s s -s tra in curves fo r P o ly f ilt e r X fa b ric (support and cover m ateria l = dry #30 Ottawa sand) S tre s s -s tra in curves fo r P o ly f ilt e r X fa b ric (support and cover m ateria l = wet #30 Ottawa sand) S tre s s -s tra in curves fo r P o ly f ilt e r X fa b ric (cover m a te ria l = dry #30 Ottawa sand; support m ateria l = fin e g ra v e l) S tre s s -s tra in curves fo r P o ly f ilt e r X fa b r ic (support and cover m ateria l = dry fin e g r a v e l ) Log E-j versus log a n fo r P o ly f ilt e r X fa b r ic (cover and support m ateria l = dry #30 Ottawa sand) e/gy versus e fo r P o ly f ilt e r X fa b ric (support and cover m ateria l = dry #30 Ottawa sand) S tre s s -s tra in curves fo r P o ly f ilt e r X fa b r ic (support and cover m ateria l = #30 Ottawa sand) S tre s s -s tra in curves fo r P o ly f ilt e r X f a b r ic, under 1/2 t s f normal pressure and various support and cover combinations S tre s s -s tra in curves fo r P o ly f ilt e r X fa b r ic under 4 t s f normal pressure f o r vario u s combinatio n s o f cover and support m a t e r ia ls S tre s s -s tra in curves fo r M ir a fi 100X fa b r ic along g rain s (suppo rt and cover m a te ria l = dry #30 Ottawa s a n d ) S tre s s -s tra in curves fo r M ira fi 100X fa b ric across g rain s (support and cover m a te ria l = dry #30 Ottawa s a n d )... 66

9 v m LIST OF ILLUSTRATIONS C o ntinue d F ig u re Page 5.14 S tre s s -s tra in curves fo r M ir a fi 500X fa b r ic along g rains (support and cover m a te ria l - dry #30 Ottawa s a n d ) S tre s s -s tra in curves fo r M ir a fi 500X fa b ric across g rain s (support and cover m a te ria l = dry #30 Ottawa s a n d ) S tru ctu re o f M ir a fi 100X and M ir a fi X S tre s s -s tra in curves fo r M ir a fi 140S fa b ric (suppo rt and cover m a te ria l = dry #30 Ottawa sand) S tre s s -s tra in curves fo r M ir a fi 140S fa b r ic (support and cover m ateria l = wet #30 Ottawa sand) S tre s s -s tra in curves fo r M ir a fi 140S fa b ric (support m ateria l = dry fin e g ra v e l; cover m aterial = dry #30 Ottawa s a n d ) S tre s s -s tra in curves fo r M ir a fi 140S fa b r ic (support and cover m ateria l = dry fin e g r a v e l ) Log Ei versus log a,, f o r M ir a f i 104S (co ver and support m ateria l = dry Ottawa sand) e/o y versus e fo r M ir a fi 104S fa b r ic (support and cover m ateria l = dry #30 Ottawa sand) S tre s s -s tra in curves fo r M ir a fi 140S fa b r ic (cover and support m a te ria l = #30 Ottawa sand) S tre s s -s tra in durves f o r M ir a fi 104S fa b ric fo r various combinations o f g e o te x tile -s o il in te rfa c e under 1 /2 t s f normal pressure S tre s s -s tra in curves f o r M ir a fi 104S fa b r ic fo r various combinations o f g e o te x tile -s o il in te rfa c e under 4 t s f normal pressure S tre s s -s tra in curves fo r Typar 3601 fa b ric (support and cover m a te ria l = dry #30 Ottawa sand)... 82

10 ix LIST OF ILLUSTRATIONS - Continued Figure Page 5.27 S tre s s -s tra in curves fo r Bidim C-34 fa b ric (support and cover m ateria l = dry #30 Ottawa sand)... 83

11 LIST OF TABLES Table Page 2.1 G e o te x tile c la s s ific a tio n P u ll-o u t te s ts w ith cohesionless s o ils and nonwoven g e o te x tile Bidim U Physical p ro p e rties o f woven g e o te x tile s Physical p ro p e rties o f nonwoven g e o te x tile s Grain s ize d is trib u tio n data fo r g r a v e l Slope (m) and y -in te r c e p t (b) values fo r the s tra ig h t lin e s o f Figures 5.8 and x

12 ABSTRACT The strength behavior o f a g e o te x tile is o f g reat s ig n ific a n c e to e v a lu a te i t s performance in con junction w ith geotechnical co n stru c tio n a c t iv it ie s. Thus a study o f the s tre s s -s tra in behavior fo r geot e x t ile s is d e f in it e ly needed. In th is th esis the re s u lts o f such a study are presented fo r a number o f g e o te x tile s having d iffe r e n t charact e r is t ic s. The fo llo w in g general approach was used: the te n s ile strength o f each g e o te x tile was determined fo r zero normal pressure, i. e., w ithout s o il in the te s t box used fo r te s tin g the g e o te x tile s. A p lo t o f the specimen width versus it s deform ation was developed to determ ine the tru e te n s ile strength o f the g e o te x tile. Tests were then performed w ith s o il above and below the g e o te x tile. An "equivalent te n s ile strength" o f the g e o te x tile was defined fo r these co n d itio n s. The e ffe c ts o f varying the type o f g e o te x tile and the type o f support and cover s o ils on the eq u ivalen t te n s ile strength were then in v e s tig a te d. Tests were performed fo r normal pressures o f 0.5 t s f, 1 t s f, 2 t s f, and 4 t s f. "Equivalent te n s ile stresses" versus s tra in s were p lo tte d fo r each normal pressure. Equations fo r the s tre s s -s tra in curves and fo r the tangent moduli as a fu n ctio n o f normal pressure were d erived. The e ffe c t o f confining pressures, cover and support m a te ria ls, and w ater content on fa b ric performance was also in v e s tig a te d. x i

13 CHAPTER 1 INTRODUCTION "G e o te x tile " is the name now u n iv e rs a lly adopted fo r fa b ric s used in geotechnical engineering. The g e o te x tile s a v a ila b le today are so diverse th a t i t is d i f f i c u l t to give a sin g le simple d e fin itio n. In g e n e ra l, however, they may be considered to be polymers formed in to porous sheets. G e o te x tile is a r e la t iv e ly hew term. I t has re c e n tly been adopted as the o f f i c i a l name fo r these m a te ria ls by the American Society fo r Testing and M a te ria ls (ASTM) Subcommittee These m a te ria ls have also been known in the past as f a b r ic s, f i l t e r fa b r ic s, geotechnical fa b r ic s, engineering fa b r ic s, construction fa b r ic s, and other names. G eo textiles are a v a ila b le in many forms. They are woven, k n itte d, and nonwoven. Some are rough, some are smooth, some are th ic k (90 m ils ), and some are th in (16 m ils ). They a ls o come in com binations o f the v a r ious types re s u ltin g in layered fa b ric s. G eo textiles are manufactured from numerous polymers. The most common are polypropylene, p o ly e s te r, nylon, and polyeth ylen e. cases more than one polymer is used in an in d iv id u a l fa b r ic. In some This a ll re s u lts in a wide v a r ie ty o f fa b ric s w ith g re a tly d iffe r e n t c h a ra c te ris tic s and a wide p ric e range. In s o il improvement a p p lic a tio n, the fa b r ic costs may range from less than a d o lla r to several d o lla rs a square yard ( B e ll, 1980). 1

14 G eotextiles are being used more and more o fte n as reinforcem ents 2 o f weak s o ils. The use o f g e o te x tile s in s o il reinforcem ent comes in a v a rie ty o f forms, as illu s t r a te d in Figure 1.1. The f i r s t ap p lic a tio n s o f these g e o te x tile s were fo r subgrade s ta b iliz a tio n where the fa b ric s were placed between the base coarse or b a lla s t la y e r and the subgrade to provide support fo r the roadway (F ig u re 1.1 a ). Such uses o f g e o te x tile s fo r reinforcem ent purposes dates back to the la te 1960s ( B e ll, 1980). Today the use o f g e o te x tile s fo r subgrade s ta b iliz a tio n is common. F i l l foundation reinforcem ent re fe rs to cases where the fa b ric is used to prevent a rupture f a ilu r e from occurring in a very s o ft foundation s o il from the dead load o f an embankment f i l l or from the a p p lic a tio n o f a liv e load o f la rg e areal exten t (Fig ure 1.1 b ). For fu rth e r re in fo rc e ment, layers o f fa b ric may be included in the embankment as needed (Fig ure 1.1 c ). This idea was reported by Iwaski and Watanabe in Possibly the g re a te s t amount o f work regarding the use o f g e o te x tile s as reinforcem ent has been done in Japan w ith the reinforcem ent o f ra ilro a d embankments. I t has also been proposed ( B e ll, 1980), th a t g e o te x tile -re in fo rc e d granular m a te ria ls be used under and/or over la rg e c u lv e rts through embank ments over very s o ft foundations in stead o f tim b er bedding as is the c u r re n t p ra c tic e. This concept is shown in Figure l. l d. The use o f geote x t ile s as reinforcem ent o f foundations fo r footin g s under or above poor s o ils has also been proposed (B assett and L a s t, 1978). This a p p lic a tio n o f the use o f g e o te x tile s is illu s t r a te d in Figure l. l e. G eo textiles have also been used as earth re in fo rc in g elements in re ta in in g w a lls. In some o f

15 Figure 1.1. Reinforced earth ap p lic a tio n s (B e ll, 1980). a. Subgrade s t a b iliz a tio n. b. S o ft foundation reinforcem ent. c. Embankment reinforcem ent. d. G e o te x tile reinforcem ent o f c u lv e rt cover and bedding. e. Footing foundation reinforcem ent. f. G e o te x tile rein fo rc ed earth w a lls.

16 3 Aggregate Surface o o G e o te x tile Figure 1.1 a. Subgrade s ta b iliz a t io n. G e o te x ti1e Figure 1.1b. S o ft foundation reinfo rcem ent.

17 4 Reinforcem ent Compaction iv Aids Figure 1.1 c. Embankment reinforcem ent. G e o te x tile G e o te x tile Figure l. l d. G e o te x tile reinforcem ent o f c u lv e rt cover and bedding.

18 5 G e o te x tile Figure l. l e. Footing foundation reinforcem ent. G e o te x tile Figure l. l f. G e o te x tile re in fo rc e d earth w a lls.

19 6 these cases the g e o te x tile s were the only re in fo rc in g elem ents. In o th e rs, the g e o te x tile s were wrapped around the s o il to form the facin g fo r the w a ll. These a p p lic a tio n s are illu s t r a te d in Figure 1. I f. G eo textiles are also used in s o il s ta b iliz a tio n as f i l t e r media fo r d rain s. In th is way, seepage w ater and other subsurface w ater can be c o n tro lle d as shown in Figures 1.2 and 1.3. G e o te x tile s are also used to a c c e le ra te v e r tic a l drainage and consequently the consolidation o f natural foundation s o il (Fig ure 1.4 ), and as ero sio n -contro l devices as illu s t r a te d in Figure 1.5. From the above discussion, i t is apparent th a t s ig n ific a n t use o f g e o te x tile s in s o il engineering a p p lic a tio n s is becoming more common. Thus f a r, most g e o te x tile a p p lic a tio n s have been fo r earth -re in fo rcem e n t purposes. Such a p p lic a tio n s re q u ire an understanding o f the strength behavior o f the fa b r ic under the range o f loading conditions i t may be subjected to in the f i e l d. O b jective and Scope o f the Work C u rre n tly, g e o te x tile s are m ostly used as a reinforcem ent mater ia l to improve weak s o il's load-bearing c a p a c ity. The mechanism d eveloped by the use o f the g e o te x tile s as a reinforcem ent m ateria l is a functio n o f the stress d is trib u tio n due to the in te rfa c e f r ic t io n between the g e o te x tile and the s o il. In the s o il-g e o te x tile -c u lv e r t system (Figure 1. I d ), the g e o te x tile becomes an in te ra c tiv e s tre s s -c a rry in g component o f the system. T h e o re tic a lly, the g e o te x tile, when embedded in s o il, is considered to be a pinned beam so th a t h o rizo n ta l and v e r tic a l

20 G e o te x tile Compacted S o il S in g le-s ized Aggregate Subsoil Figure 1.2. French drain protected w ith g e o te x tile (Commercial D isp lays, 1980). G e o te x tile Compacted S oil P erforated. Pipe S in g le-s ized Aggregate F ig u re 1.3. C o nventio nal tre n c h d ra in c o n s tru c te d w ith a d u a l-la y e re d aggregate f i l t e r and a d ra in p ip e in fin e - g r a in e d s o ils (Commercial D is p la y s, 1980).

21 s T1 I n!///// /- Pavement v I Base F i l t e r G e o te x tile Coarse A ggregate/ Water Transport Medium F i l t e r G e o te x tile Subgrade Figure 1.4. Blanket drain constructed w ith g e o te x tile (Commercial D isplays, 1980). (o p tio n a l) Rip Rap Stone G e o te x tile Optional Bedding Blanket (crushed stone, sand, e t c.) Water Level Bottom Toe (o p tio n a l) Figure 1.5. Embankment s ta b iliz a tio n -e ro s io n control (Commercial D isplays, 1980).

22 9 movements a t the e x tre m itie s are prevented. Rotation is allowed so th a t tension in the g e o te x tile is developed as loads are a p p lie d. P r a c tic a lly, in order to design g e o te x tile -re in fo rc e d systems, the e ffe c t o f s o il confinem ent and o th e r placement fa c to rs on th e performance o f the geot e x t ile must be evaluated. This research provides an in s ig h t in to the e ffe c t o f s o il confinem ent, cover and support m a te ria ls and s o il m oisture content on the te n s ile strength parameters o f selected g e o te x tile s. The o b je c tiv e o f th is study was to in v e s tig a te the te n s ile strength performance o f a number o f com m ercially a v a ila b le g e o te x tile s. Two types o f g e o te x tile were studied: woven and nonwoven. The types o f woven g e o te x tile s tested were P o ly f ilt e r X, M ir a fi 100X along grains and across g ra in s, and M ir a fi 500X along grains and across g ra in s. The nonwoven g e o te x tile s studied were M ira fi 140S, Typar 3601, and Bidim C-34. The tru e te n s ile strength o f each o f the aforem entioned geotext ile s was determined a t zero confinin g pressure. The "eq u ivalen t te n s ile strength" o f the g e o te x tile was determined a t normal pressures o f 1 /2 t s f, 1 t s f, 2 t s f, and 4 t s f. This in v e s tig a tio n was accomplished as fo llo w s : 1. A special sample box was designed and b u ilt to perform the te n s ile strength te s t o f the g e o te x tile s in a conventional d ir e c t shear device. 2. A s tra in ra te o f 0.05 in/m in was used fo r a l l g e o te x tile te n s ile te s ts. 3. The th ickn ess o f each g e o te x tile was determ ined using ASTM

23 10 4. The v a ria tio n o f the specimen's la te r a l width w ith it s transverse deform ation was determ ined during loading f o r zero normal p ressure. 5. "E quivalent te n s ile stress" was determined by d iv id in g the p u llout load by the specimen's e ffe c tiv e width and thickness. The lo n g itu d in a l s tra in was also c a lc u la te d as the lo n g itu d in a l deform ation divided by the i n i t i a l length o f the specimen. 6. The s tre s s -s tra in curve was determined a t zero normal pressure, fo r each type o f g e o te x tile used. 7. The "eq u ivalen t te n s ile strength" o f each g e o te x tile was in v e s tigated, under normal pressures o f 1 /2 t s f, 1 t s f, 2 t s f and 4 t s f, fo r the fo llo w in g support and cover conditio n s: a. Dry #30 Ottawa sand fo r both cover and support m a te ria ls fo r each type o f g e o te x tile used. b. Wet #30 Ottawa sand fo r both cover and support m a te ra ils fo r P o ly f ilt e r X and M ir a fi 140S g e o te x tile s. c. Dry #30 Ottawa sand f o r cover and dry f in e gravel f o r supp o rt fo r P o ly f ilt e r X and M ira fi 140S g e o te x tile s. d. Dry fin e gravel fo r both cover and support m a te ria ls fo r P o ly f ilt e r X and M ir a fi 140S g e o te x tile s. 8. The s tre s s -s tra in curves fo r each combination o f s o il and fa b r ic tested were studied fo r the various normal pressures. 9. Equations were developed fo r the s tre s s -s tra in curves and fo r the tangent moduli as a fu n ctio n o f normal pressure. This was done only fo r P o ly f ilt e r X woven g e o te x tile and M ir a fi 1405

24 11 non-woven g e o te x tile, fo r s o il conditions described in 7a. Howe v e r, a s im ila r procedure could be follow ed to obtain the same re la tio n s h ip s fo r the o th er g e o te x tile s and s o il support/cover conditio n s. in Figure 1.6. A summary o f the te s tin g program fo r th is in v e s tig a tio n is shown

25 G e o te x tile Type Sand-Sand In te rfa c e Gravel-Sand In te rfa c e G ravel-g ravel In te rfa c e P o ly f ilt e r X Xa X X Woven M ir a fi loox Along Grains X Across Grains X Along Grains X M ir a fi 500x Across Grains X M ir a fi 140S xa X X Nonwoven Typar 3601 X Bidim C-34 X a. Tests were also performed fo r wet in te rfa c e s. Figure 1.6. Summary o f te s tin g program. - - Each series included te s ts a t normal pressures o f 0 t s f, 0.5 t s f, 1 t s f, 2 t s f, and 4 t s f. A ll s o ils were a ir -d r y except where noted.

26 CHAPTER 2 REVIEW OF LITERATURE General Review G e o te x tile C la s s ific a tio n A g e o te x tile c la s s ific a tio n according to s tru c tu re filam ents and bonding o f the g e o te x tile is presented in Table 2.1. The woven g e o te x tile s are u su ally th in and have simple uniform pores. They consist o f filam en ts or yarns in te rla c e d in simple re c ta n g u la r p a tte rn s, fo r example, see Figure 3.1. R e la tiv e to t h e ir lig h t w eig ht, they are q u ite strong. The strength o f the woven g e o te x tile s may be the same along or across (perpendicu lar to ) the d ire c tio n s o f the fila m e n ts ; or they may be stronger in one d ire c tio n than in the o th e r. The s tre s s -s tra in c h a ra c te ris tic s o f these m a te ria ls may be d iffe r e n t on the bias than in the d ire c tio n o f the fila m e n ts. The strength o f the woven g e o te x tile s changes w ith the nature o f the fila m e n ts. G e o te x tile s may be woven from monofilaments which are sin g le strands o f extruded polymer. These are u su ally in te rm e d ia te - strength g e o te x tile s. G e o te x tile s o f in term ed iate to very high strength are woven o f m u ltifila m e n t yarns. The strongest o f a ll g e o te x tile s are manufactured in th is manner and they are somewhat more expensive than the monofilament g e o te x tile s. 13

27 Table 2.1. G e o te x tile c la s s ific a tio n ( B e ll, 1980) S tru c tu re Filam ent Bonding M onofilam ent Heat-Bonded None Woven M u lti fila m e n t None S l i t Film None K n itte d M u ltifila m e n t None Nonwoven S tap le Filam ent Continuous Filam ent Needle-Punched Heat-Bonded Resin-Bonded Combination Needle-Punched Heat-Bonded Resin-Bonded Combination Combination Woven and Nonwoven Combinations o f Above Combinations o f Above Special Special Special

28 15 The k n itte d g e o te x tile s are u su ally manufactured from m u ltifila m e n t yarns and have been used very l i t t l e in s o il improvement a p p lic a tio n s, probably because o f costs. Nonwoven g e o te x tile s are coherent fa b ric s which consist o f sheets formed o f filam ents in more o r less random order and bonded to g e th e r; fo r example, see Figure 3.2. Nonwoven g e o te x tile s tend to be inexpensive because they are manufactured continuously and a u to m a tic a lly. These geot e x t i l e s are formed from f in e extruded m onofilam ents. Nonwoven geotext ile s are divided in to two kinds. In some forming processes, the f i l a ments are continuous. These are r e fe r r e d to as "continuous fila m e n ts." In o th er forming processes, the fila m e n t is chopped in to short lengths. These are re fe rre d to as "staple fila m e n ts." The continuous fila m e n t fa b ric s tend to have the same mechanical p ro p e rties in a ll d ire c tio n s, although there might be some s ig n ific a n t d iffe re n c e s between the propertie s o f fila m e n t fa b ric s produced by d iffe r e n t m anufacturers. The sta p le filam ents may be random, in which case they have s im ila r p ro p e rtie s in a ll d ire c tio n s, o r they may have a p re fe rre d o rie n ta tio n which makes them stronger in one d ire c tio n than in the perpendicular d ire c tio n. A s ig n ific a n t d iffe re n c e in p ro p e rties between types o f nonwoven g e o te x tile s is due to the way the fib e rs are bonded to g eth er. In the needle-punched g e o te x tile s the filam en ts are entangled by pushing barbed needles through the f ib e r mat. These g e o te x tile s are th ic k and have the appearance o f f e l t. During heat bonding the loose f ib e r mat is passed between heated r o lle r s which cause the fila m e n ts to bond to g eth er by w elding. This re s u lts in a th in n e r, s t i f f e r s tru c tu re than needle-

29 16 punching. Resin bonding is le s s common than needle-punching or h e a t bonding. In th is process a resin is introduced in to the g e o te x tile which cements the fib e rs to g e th e r. There are also nonwoven g e o te x tile s which combine two or more bonding processes ( B e ll, 1980). D ifferen ces in the physical p ro p e rties among nonwoven g e o te x tile s may be very g re a t, depending upon the nature o f the fila m e n t and the bonding process. They a l l have ir r e g u la r and non-uniform pore s tr u c - l tu re s. For the same weight o f m a te r ia l, they tend to be somewhat weaker and have considerably lower moduli than the woven g e o te x tile s. Some g e o te x tile s are constructed o f a combination o f woven and nonwoven component. The woven component is u su ally used to provide desired strength and modulus c h a ra c te ris tic s. The nonwoven components may be used to p ro te c t the woven from abrasion and/or to provide desired pore c h a ra c te ris tic s. There are also special g e o te x tile s on the m arket. These u su ally consist o f extruded forms entangled w h ile they are s t i l l s o ft so th a t they weld to gether ( B e ll, 1980). G e o te x tile Polymers The common polymers used in the manufacture o f g e o te x tile are polypropylene, p o ly e s te r, polyethylene and nylon. C u rre n tly, polypropylene is the most w idely used polymer and nylon is the le a s t w idely used. The polymers have many s im ila r it ie s, although they have s ig n ific a n t d i f ferences. They are a l l h ig h ly re s is ta n t to the m oistu re, tem perature, chemical and b io lo g ic a l environment norm ally occurring in s o ils in s itu. They may, however, be damaged by extrem ely strong acids o r bases. They

30 17 a ll have r e la t iv e ly high s tre n g th -to -w e ig h t r a tio s. The polypropylene fa b ric s have p a r tic u la r ly good s tre n g th -to -c o s t r a tio s. I t is d i f f i c u l t to rank the polymers w ith respect to strength because the d e ta ils o f how the polymer is formed in to a fib e r g re a tly in flu ence the strength o f the f ib e r. T h e re fo re, the r e la tiv e strengths o f the d iffe r e n t polymers may change depending upon the m anufacturing process. For example, p o lyester fib e rs tend to have less tendency to creep than do the o th er polymers, so they tend to m aintain t h e ir strength over tim e. G e n e ra lly, u lt r a v io le t lig h t degrades the polymers used in fa b r ic s. T h e re fo re, the polymers must be tre a te d to s ta b iliz e them against u lt r a v io le t degradation or the g e o te x tile s must be protected against prolonged exposure to s u n lig h t ( B e ll, 1980). G e o te x tile T e n s ile Strength There are im portant questions as to how the te n s ile strength o f the fa b ric should be measured. or m u ltia x ia l te s ts in loading? Should i t be measured by simple u n ia x ia l F u rth e r, should th ere be a s p e c ific d e s ira b le r e la tiv e geometry o f laborato ry te n s ile te s t specimens? As fa b r ic specimens are p u lle d in tension they tend to reduce in t h e ir la te r a l dimension. I f the fa b ric s are re s tra in e d so th a t th ere is no s tra in normal to the d ire c tio n o f the lo ad, the s tre s s -s tra in curve obtain ed is s ig n ific a n tly d iffe r e n t from th a t obtained i f the fa b ric is fre e to move la t e r a lly. B ell (1980) performed te n s ile te s ts w ith the fa b r ic confined between th in sand la y e rs. He demonstrated th a t the s tre s s -s tra in curves

31 fo r such conditions are s ig n ific a n tly d iffe r e n t from those fo r the fa b 18 r ic tested in is o la tio n. Salomone e t a l. (1980) observed th a t fa b r ic s tra in s measured in la b o ra to ry p u ll-o u t te s ts were grossly d iffe r e n t from the s tra in s predicted from the fa b ric modulus measured in is o la tio n. Other im portant questions regarding the te s tin g fo r the te n s ile strength o f fa b ric s must be considered. For example, what is the e ffe c t o f the ra te o f loading? I t is known th a t te n s ile strength o f geotext ile s is lo ad -rate -d e p en d e n t, but very l i t t l e is known as to why th is is so or how i t can be expressed q u a n tita tiv e ly. G e o te x tile m ateria l p ro p e rties are also tem perature-dependent, but th ere are no methods to date (1981) to account fo r th is e f f e c t. Another very im portant question is how to d efin e the f a ilu r e s ta te o f the fa b ric? Some consider i t to be the te n s ile stress a t ru p tu re ; others consider i t to be the te n s ile stress a t a c e rta in s tra in le v e l. accepted c r ite r io n in th is regard. U n fo rtu n a te ly, th ere is no g e n e ra lly In a d d itio n, g e o te x tile s are subject to creep and fa tig u e. Although these e ffe c ts have been studied very l i t t l e, i t has been shown th a t d iffe re n c e s in polymer type and in fa b ric construction are very im portant w ith respect to these p ro p e rtie s. In reinforcem ent a p p lic a tio n s, the f r ic t io n between the s o il and the fa b ric is a v it a l concern. This in te rfa c e f r ic t io n is a fu n ctio n not only o f the f a b r ic, but also o f the s o ils involved and the normal stress between the s o il and the fa b r ic. A standard f r ic t io n te s t does not e x is t fo r f a b r ic -s o il in te rfa c e s. The g e o te c h n ic a l e n g in e e r has v e ry l i t t l e in fo rm a tio n o r p re c e dent on some im p o rta n t e n g in e e rin g c h a r a c te r is tic s o f th e f a b r ic such as

32 19 the te a r re s is ta n c e, puncture re s is ta n c e, and abrasion re s is ta n c e. The d e fin itio n s o f these terms are not u n iv e rs a lly accepted, and th ere is no general agreement concerning t h e ir mechanisms or importance ( B e ll, 1980). Experiments o f Soil Reinforcement w ith G e o te x tile s G eo textiles are used more and more o ften fo r reinforcem ent in unpaved roads, earth embankments, and in m u ltila y e r s o il-g e o te x tile systems. For each o f the a p p lic a tio n s, i t is necessary to measure the s o il-g e o te x tile shear strength c h a ra c te ris tic s when the g e o te x tile is used as a reinforcem ent. This is done fo r two purposes: f i r s t, to evaluate the a b i l i t y o f the g e o te x tile to a c t as a reinforcem ent; and second, to determine whether the g e o te x tile could a c t as a s lip surface in s id e the e a rth mass. This second item is im p ortan t even when the geot e x t ile is used fo r purposes o th er than reinforcem ent. The paper published by C o llio s e t a l. (1980) contains the re s u lts o f experim ental te s ts conducted using s p e c ia lly designed te s tin g equipment to address the two aforementioned p o in ts. Since th a t work is d ir e c t ly re le v a n t to the present research, the d e ta ils o f th a t study are described h ere. T es tin g Equipment A s p e c ia lly designed shear box was developed to perform th e p u l l out te s ts. The shear box was made up o f two separate pieces. The spacing between the two halves o f the box could be adjusted to a llo w the placement o f a g e o te x tile in the shear plane. The s ize o f the box was

33 20 larg e enough to accommodate p a r tic le sizes as la rg e as coarse g ra v e l. The box dimensions were in. in the d ire c tio n o f displacem ent, 9.84 in. w ide, and 7.87 in. high. The a v a ila b le loading equipment allowed maximum normal ( v e r t ic a l) and te n s ile (h o riz o n ta l) forces o f 6.74 kip s. p Since the area o f the box ( a t zero displacem ent) was f t, th e m aximum normal stress th a t could be applied was 3.12 t s f. This stress c o r responds to an overburden pressure o f about 49 f t. o f e a rth. The displacement ra te used in a ll te s ts was.24 in./m in. Figures 2.1, 2.2, and 2.3 show the various featu res o f the te s t box. T es tin g Procedure In running the p u ll-o u t te s ts, the two halves o f the shear box were fix e d and one end o f the g e o te x tile sample was subjected to a h o rizontal fo rc e. To avoid necking o f the g e o te x tile portio n which was in the box, a row o f small v e r tic a l pins was located on each side o f the box (Fig ure 2.2). During each o f the p u ll-o u t resistan ce te s ts o f the g e o te x tile, the normal lo ad, P, was kept constant. T h e re fo re, i t was assumed th a t the normal s tre s s, o, was also constant, i.e., where = area o f the box (1.0 8 f t ^ ). Applied h o rizo n tal fo rce and re s u ltin g displacem ent were re c o r ded a t various tim es during each t e s t. The recorded displacem ent c o r responded to the displacem ent o f the e x tre m ity o f the g e o te x tile sample

34 21 -> T Figure 2.2. Pull-out test apparatus (from Collies et a!., 1980). -- Arrow shows the pins used to prevent necking of the geotextile sample.

35 2 2 Figure 2.3. Detailed view of the pull-out test apparatus (from Collies et a l., 1980). -- Upper half of the box is empty and loading plate has been removed.

36 23 which was attached to the h o rizo n tal loading device. The displacem ent o f the other extrem ity o f the g e o te x tile sample was also recorded in order to determine the area o f the g e o te x tile, A^, in sid e the shear box. Graphical Representation o f S o il-g e o te x tile Kinematics Figure 2.1 is a schematic th a t shows a g e o te x tile specimen in the shear box, in cro s s -s e c tio n, under a normal pressure. One end o f the specimen is attached to the h o rizo n tal p u ll-o u t loading d evice, w hile the opposite end is fre e and can s lip along the h o rizo n tal plane under the normal pressure when the h o rizo n tal load is a p p lie d. The g e o te x tile specimen undergoes elongation during the p u ll-o u t te s ts. D iffe re n t points o f the g e o te x tile sample undergo d iffe r e n t displacem ents. This is illu s t r a te d in Figure 2.4 where three points o f the g e o te x tile sample are considered. The p o in t A is where the g e o te x tile sample is attached to the h o rizo n tal loading device. The poin t M is located a t the middle o f the g e o te x tile sample. extrem ity o f the g e o te x tile sample. The p o in t F is located a t the fre e Point A moves a distance x ^ as soon as a small h o rizo n tal fo rce T-j is a p p lie d. However, a t th a t tim e, points M and F do not move -(x^^ = x ^ = 0) because the shear stresses generated by the fo rc e, T-j, a t M and F, are not s u ffic ie n t to overcome the shear resistance m obilized between the s o il and g e o te x tile. When the h o rizo n tal fo rc e T-j is increased to Tg, A and M move to x^> and x ^, respect iv e ly. The p o in t F s t i l l does not move fo r the reason noted above ( i. e., Xpg = 0 ). F in a lly, F moves a distance Xpg when T reaches the value o f Tu-j. At th a t p o in t the f u l l in te rfa c e shearing resistan ce is m obilized and the g e o te x tile sample moves as a whole. The h o rizo n ta l

37 24 >x U M F,M,A *» x '2 '1 F M U T Z T -t z z : KF3 XM3 I xag A T F M Figure 2.4. S o il-g e o te x tile kinem atics associated w ith progressive f a ilu r e in a p u ll-o u t te s t ( a f t e r C o llio s e t a l., 1980).

38 25 force even has a tendency to decrease s lig h tly since the area o f the g e o te x tile portio n in sid e the box begins to decrease as the fre e end, F, is pulled out. In te rp re ta tio n o f P u ll-o u t Test Results Shear stresses develop on the g e o te x tile surface when the p u llout fo rce is a p p lie d. However, the shear stresses are not uniform ly d is trib u te d (Delmas, Gourc and G iroud, ). I t is reasonable to assume th a t a uniform d is trib u tio n o f the shear stresses leads to a c o rre c t value o f the shear strength i f the area o f th e g e o te x tile sample is equal to the cross-sectio n al area o f the box. For the sake o f convenience, the m ateria ls in the upper and lower halves o f the box are c a lle d cover and support, re s p e c tiv e ly. Two s itu a tio n s must be considered: 1. The same s o il is used fo r cover and support. In th is case, the average shear s tre s s, t, between the s o il and g e o te x tile is given by: where Ag = surface area o f the g e o te x tile For a given s e rie s o f te s ts, the values o f Tu- t are p lo tte d versus the normal stress a defined by Equation 2.1. An example o f such a p lo t is shown in Figure 2.5. From the s tra ig h t lin e thus obtained, i t is possible to determine the in te rfa c e f r i c tio n an g le, $, and the adhesion, c, between the cover m ateria l and the g e o te x tile.

39 26 By comparing c and <J> w ith the in te rn a l f r ic t io n angle, 4>, and the cohesion c, o f the cover and support m a te r ia l, two "contact e ffic ie n c ie s " can be defined. One is re la te d to f r i c tio n, and the other to cohesion, as fo llo w s : pp _ tanj) u <i> tan * (2.3 ) (2.4 ) These concepts are s im ila r to those developed by Potyondy (1961) fo r s o il- p ile m ateria l in te rfa c e s. 2. D iffe r e n t s o ils are used fo r cover and support. In th is case i t is possible to account fo r the d iffe re n c e as fo llo w s : _T A 9 (2.5 ) where TgC = average shear stress between g e o te x tile and cover Tgs = average shear s tre s s between g e o te x tile and support ^ I t is im possible to determ ine Tgc and Tgs s e p a ra te ly, unless one o f the m a te ria ls is cohesion!ess and the other is f r ic t io n le s s. I f th a t is the case, c and *" can be determined by p lo ttin g (Tgc + Tg s ) u l t versus a, as shown in Figure 2.6. Contact e f f i ciencies are then defined by Equations 2.3 and 2.4 as they are f o r the case when cover and support m a te ria ls are th e same. I t should be noted th a t a contact e ffic ie n c y o f one means th a t the contact between the g e o te x tile and the cover and support s o ils is perf e c t, i. e., f a ilu r e can take place w ith in the s o il mass as e a s ily as

40 27 Figure 2.5. Curves Ty-j^ versus o fo r id e n tic a l cover and support m a te r ia l. (a ) Cohesionless m a te ria l; and (b) F ric tio n le s s m ateria l (C o llio s e t a l., 1980). Figure 2.6. Curve (Tgc + Tgs) u^t versus a in which one o f the m a te ria ls in contact w ith the g e o te x tile is cohesionless and the o th er one is f r i c t i o n less (C o llie s e t a l., 1980).

41 28 along the s o il-fa b r ic in te rfa c e. In some cases the u ltim a te shear strength th a t can be m obilized a t the s o il-g e o te x tile in te rfa c e is less than the shear strength o f the confining s o i l. The contact e ffic ie n c y fo r the p u ll-o u t te s t in a ll such cases is less than one, i. e., the u l tim ate shearing resistan ce th a t can be m obilized along the s o il-g e o te x tile in te rfa c e is less than the shear strength of the s o i l. T h e re fo re, f a ilu r e w ill take place by slippage o f the g e o te x tile. Slippage occurs when the g e o te x tile is ta u t. The g e o te x tile becomes ta u t only a f t e r la rg e d is placements o f points on the g e o te x tile have occurred w ith reference to the surrounding s o il. These la rg e displacements re s u lt in a re o rie n ta tio n o f the s o il p a rtic le s along the in te rfa c e and, consequently, in a reduction o f the shear strength in th a t zone. Contact e ffic ie n c y is a dominant fa c to r fo r the s o il-g e o te x tile in te rfa c e. It s evalu a tio n is necessary both to determine the a b i l i t y o f a g e o te x tile to act as a reinforcem ent and to determine whether i t can act as s lip surface in sid e an earth mass. Test R esults w ith Cohesionless S o ils P u ll-o u t te s ts on nonwoven f a b r ic, Bidim U44, were conducted by C o llie s e t a l. (1980) w ith the support and cover m a te ria l id e n tic a l. Table 2.2 shows the te s t re s u lts obtained f o r various cohesionless mater ia ls w ith d iffe r e n t a n g u la rity and s ize o f s o il p a r tic le s. The contact e ffic ie n c y and f r ic t io n values are sm aller fo r rounded gravel than fo r crushed g ra v e l. C o llie s e t a l. (1980) explained th is by noting th a t the g e o te x tile displacem ent was la rg e r in the case o f rounded gravel as the confinin g m a te ria l. They do not o ffe r an explanation o f why th is is so,*

42 29 Table 2.2. P u ll-o u t te s ts w ith cohesionless s o ils and nonwoven g e o te x tile Bidim U44 (C o llio s e t a l., 1980) Type Sand Rounded Gravel Crushed Gravel B a lla s t Stones Support s o il i< > Torn is id e n tic a l to cover s o il tan<jt tan<}> bo o In the s ta te o f the a r t th ere are also experim ental studies performed on cohesive s o ils -g e o te x tile s in te ra c tio n s. This is not discussed in th is th e s is, because i t is not in the scope o f th is th e s is research.

43 CHAPTER 3 PROPERTIES OF MATERIALS USED IN THIS RESEARCH In t h is research various types o f g e o te x tile s were used in conju n ctio n w ith two s o il types. The s o il types were #30 Ottawa sand and a fin e riv e r-ru n gravel G e o textiles As in d ic ated p re v io u s ly, engineering g e o te x tile s, which are sometimes c a lle d " p la s tic f i l t e r fa b ric s " o r " p la s tic f i l t e r c lo th," are e ith e r woven or nonwoven. Both types were used in th is research. Typical specimens o f each are shown in Figures 3.1 and 3.2 fo r woven and nonwoven g e o te x tile s, re s p e c tiv e ly. A review o f the a v a ila b le lit e r a t u r e in d ic ated th a t th ere is a lack o f inform ation on the engineering p ro p erties o f g e o te x tile s. In a d d itio n, th ere are no w ell-developed te s tin g c r i t e r i a a v a ila b le fo r the evaluation o f g e o te x tile s as engineering m a te ria ls. Tables 3.1 and 3.2 give a summary o f the a v a ila b le engineering p ro p e rtie s fo r the woven and nonwoven g e o te x tile s, re s p e c tiv e ly, used in th is research. Sand and Gravel Sand and gravel were used as the confinement m a te ria ls fo r t e s t ing the g e o te x tile s. The sand was a #30 Ottawa sand having an approxim ate bulk dry d e n s ity, y^, o f 90 p c f. 30

44 31 (b) (c) Figure 3.1. Woven geotextiles. -- (a) P o ly filte r X; (b) M ira fi 100X; (c) M ira fi 500X.

45 (b) Figure 3.2. Nonwoven geotextiles. -- (a) M irafi 140$; (b) Typar 3601; (c) Bidim C-34.

46 33 Table 3.1. Physical p ro p e rties o f woven g e o te x tile s (from Commercial D isp lays, 1980) G e o te x tile * P o ly f ilt e r X M ir a fi 100X M ira fi 500X Filam ent Type Polypropylene Polypropylene Polypropylene Grab T en sile Strength (lb s ) ASTM D1682 NAa Grab Elongation (%) ASTM D Thickness (m ils ) ASTM D P erm eability (cm/sec) NAa Weight? (lb /y d 2 ) * Cost $/yd 2 : $.70 - $3.75 S p e c ific g ra v ity : a NA = Not A v a ila b le.

47 34 Table 3.2. Physical p ro p e rties o f nonwoven g e o te x tile s (from Commercial D isp lays, 1980) G e o te x tile * M ir a f i 140S Typar 3601 Bidim C-34 Filam ent Type Bicomponent Fibers o f Polypropylene and Polyethylene P o lyester Continuous Fiber Polypropylene Grab T en sile Strength (lb s ) ASTM D Grab Elongation (%) ASTM D Thickness (m ils ) ASTM P erm eability (cm/sec) Weight (lb /y d 2 ) * Cost #/yd2 : $.70 - $2.75 S p e c ific g ra v ity :

48 The American Society fo r Testing and M a te ria ls (ASTM) standard te s tin g method D was follow ed in obtaining the grain s ize d is trib u 35 tio n fo r the g ra v e l. The re s u lts are shown in Figure 3.3 and tab u lated in Table 3.3. The shape o f th is curve and the calc u la te d Hazen's u n i- Dcrx fo rm ity c o e ffic ie n t (U 3.5 ) both in d ic a te th a t the gravel had a uniform grad atio n. Table 3.3. Grain s ize d is trib u tio n data fo r gravel Sieve Size % Passing 1-1/ 2" 3/4" 3/8" #4 # , #10 0

49 36 -r= 50 #10 #4 3/8" 3/4" 1-1/2" Sieve D esignation Figure 3.3. Grain s ize d is trib u tio n curve fo r g ra v e l.

50 CHAPTER 4 TESTING EQUIPMENT AND PROCEDURE Testing Equipment D ire c t Shear Device A ll te n s ile strength te s ts were performed using the d ire c t shear device a t the S o ils Laboratory o f the C iv il Engineering Department a t the U n iv e rs ity o f A rizona. The device was m odified to allo w a p p lic a tio n o f various normal pressures v e r t ic a lly and to perm it loading h o riz o n ta lly w ithout movement o f the sample box. Measurements could be made o f the v e r tic a l (expansion o r c o n tra c tio n ) and h o rizo n tal (elo n g atio n ) d is placements during lo adin g. The ra te o f h o rizo n tal displacem ent was contro lle d by an e le c t r ic motor th a t had a rh eostat (Fig ure 4.1 ). Sample Box A s p e c ia lly designed sample box was used to perform th e geotext i l e te n s ile te s ts. The box was made up o f two pieces which could be connected together by two screws s im ila r to a conventional d ir e c t shear device shear box. The spacing between the two pieces o f the box could be adjusted to allo w the placement o f a g e o te x tile specim en.in the h o rizontal plane between the support (a t the bottom) and cover (a t the top) m a te ria ls. When assembled, the box was a square w ith In te r io r side dimensions o f 2.5 in. and a height o f 1.5 in. A square cover p la te 37

51 3 8 Figure 4.1. D irect shear device.

52 s lig h tly less than 2.5 in. on a s id e, was made to cover the top surface 39 o f the box area. This cover p la te tra n s fe rre d the normal load from the te s t device to the s o il m aterial contained in the box. A 1 /2 in. connecting b o lt was also made to a tta ch the g e o te x tile specimen to the h orizontal loading arm o f the te s tin g device (Figure 4.2 ). G e o te x tile Specimen To make sure the g e o te x tile specimen received a uniform ly d is t r ib uted normal pressure from the v e r tic a l load head, i t was cut in a 2 in. square. Thus, the g e o te x tile specimen could be centered in the box and it s loading edge confined under the normal pressure during loading u n til f a ilu r e. The loading side o f the specimen and it s opposite extrem ity were glued and r iv e tte d between two th in pieces o f sheet metal th a t formed a type o f c lip (Figure 4. 3 ). The loading edge was connected to the h o rizo n tal loading arm o f the d ir e c t shear d evice, w hile the opposite extrem ity was fix e d to the f a r side o f the box. Testing Procedure Test specimens were placed on top o f support m a te ria l which was introduced in to the bottom h a lf o f the sample box a t a predeterm ined dry u n it weight (y^ = 90 pcf fo r #30 Ottawa sand; y^ =108 pcf fo r fin e g ra v e l). The top h a lf o f the sample box was then positioned over the bottom h a lf and fastened by han d-tightenin g the two connecting screws. Care was exercised in placing the g e o te x tile specimen th a t the sheet metal connecting p la te f i t in the grooves notched in to the upper and lower p o rtio n o f the box. The cover m ateria l was then introduced in to

53 Figure 4.2. Sample box.

54 Figure 4.3. Geotextile specimen.

55 the top h a lf o f the sample box a t the same required dry u n it weight as 42 the support m a te ria l. A fte r the metal cover square p la te was placed on the top o f the cover m a te r ia l, the loading head o f the te s t device was lowered to make contact w ith i t. Following a p p lic a tio n o f the normal lo ad, the sheet metal connector was attached to the h o rizo n tal loading arm o f the d ir e c t shear device. The wet te s t specimens were prepared in the same way as the dry samples except the samples were soaked in w ater fo r 24 hours before te s tin g. A ll p u ll-o u t te s ts were performed a t a h o rizo n tal displacem ent ra te o f.05 in /m in. The f i r s t two readings fo r the p u ll-o u t load were recorded fo r the f i r s t.01" and.02" o f loading deform ation. Then, readings fo r the p u ll-o u t load were recorded fo r.02" increments u n til.2" o f deform ation occurred; then readings were taken a t.05" increments u n til.5" o f to ta l g e o te x tile h o rizo n tal loading deform ation occurred. By using th is procedure, the low stress range o f the s tre s s -s tra in (lo a d - deform ation) curve was w ell d efin ed. As in d icated p re v io u s ly, a l l specim en-soil com binations were te s te d a t normal pressures o f 0.5 t s f, 1.0 t s f, 2.0 t s f and 4.0 t s f. The te s t was performed by p u llin g one end o f the g e o te x tile specimen w h ile holding the o th e r extrem ely fix e d. C o llio s e t a l. ( ), in the experim ental te s tin g, prevented the g e o te x tile from necking down upon a p p lic a tio n o f the h o rizo n tal load by p u ttin g a row o f small v e r tic a l pins on each side o f the box (F ig u re 2.2 ). When the h o rizo n ta l load was ap p lied i t was possible fo r these pins to te a r up the g e o te x tile sample a t the pin puncture points as the

56 43 g e o te x tile tends to neck down. Furtherm ore, as can be noticed from Figure 2.3, f a ilu r e o f the g e o te x tile sample happens outside the confined g e o te x tile p o rtio n. In th is research, g e o te x ti1e s - f ie ld s itu a tio n s were sim ulated in the la b o ra to ry by keeping the g e o te x tile confined under the normal pressure during h o rizo n tal loading u n til f a ilu r e. A lso, the g e o te x tile sample was fre e to deform tra n s v e rs e ly so th a t necking could occur in the p ortio n o f the sample th a t was under normal stress ju s t as i t could in the f ie l d.

57 CHAPTER 5 PRESENTATION AND DISCUSSION OF TEST RESULTS S tre s s -s tra in curves were used to evaluate the te n s ile strength c h a ra c te ris tic s o f the g e o te x tile s te s te d. To develop such curves, p lo ts o f v a ria tio n o f sample w idth versus loading deform ations fo r each o f the g e o te x tile s had to be obtained f i r s t. These are shown in Figure 5.1. T en sile stresses were computed by d iv id in g the h o rizo n ta l load by the reduced cro ss-sectio n al area o f the fa b ric (A ^ ), i. e., A^ equals the reduced la te r a l w idth o f the specimen times it s th ickn ess. I t was assumed th a t the thickness o f the specimen did not change during lo ad in g, even in the reduced sectio n. I t was reasonable to assume a ls o, th a t the amount o f necking o f the confined g e o te x tile a t a given h o rizo n tal deform ation was the same amount o f necking o f the unconfined g e o te x tile a t the same h o rizo n ta l deform ation. The s t r a in, c, was computed by d iv id in g the h o rizo n tal change in length (loading deform ation) by the o rig in a l length o f the fa b r ic specimen. As shown in Figure 2.4, d iffe r e n t points o f the g e o te x tile sample can be expected to e x h ib it d iffe r e n t displacem ents. Under normal pressures, on, when the fa b r ic is p u lle d o u t, shear stresses get m obilized along the surface area o f the g e o te x tile sample. The magnitude o f the surface shear stress is <f + antan<jt; where <jt and ct are the in te rfa c e f r ic t io n angle and the adhesion, re s p e c tiv e ly, between the confining 44

58 45 Width w (in ) O Woven G e o textiles Typar 3601 M ir a fi 140S Bidim C D eform ation6 (in ) Figure 5.1. Specimen w idth versus h o rizo n ta l deform ation fo r g e o te x tile s studied (unconfined lo a d in g ).

59 m aterial and the g e o te x tile. However, because displacements are v a r i able along the length o f the f a b r ic, the shear stresses are not uniform ly 46 d is trib u te d. G eo textiles were cut in a way th a t th e fa b ric specimens could be stretched out up to 25 percent s tra in and s t i l l remain t o t a lly w ith in the normal p ressure. Figure 5.2a shows the h o rizo n ta l forces and in te rfa c e shear stresses actin g on the g e o te x tile specimen. P «-L-r Figure 5.2. H o rizo n tal forces and in te rfa c e shear stresses actin g on g e o te x tile specimen. (a ) M o b iliz a tio n o f the shear stresses; (b ) Cross-section A-A. Im m ediately, a f t e r applying the h o rizo n tal fo rce P from the d ire c t shear device on the g e o te x tile specimen, shear stresses get m obilized on the g e o te x tile -s o il in te rfa c e. This shear stress m o b iliz a tio n on the to p, x s t, and the bottom, Tsb, o f the g e o te x tile -s o il in te rfa c e is due to the applied normal pressure. The e q u ilib riu m le n g th, Le, is th a t

60 47 portion o f the g e o te x tile where shear stresses get m obilized under a c e rta in normal pressure fo r a given h o rizo n tal load o f magnitude P. There w ill be no movement and no te n s ile stress in the g e o te x tile in length L which is beyond L^. and d is trib u tio n is not uniform even w ith in L^. By summing the h o rizo n ta l forces fo r Figure 5.2 a, we get: (x s t + Tsb)Afe = P; where Afe = Le times the average la te r a l w idth o f the fa b ric (W,lf_ ). I f a cro ss-sectio n A-A is cut a t a length L less avg c than Le> the fo rce e q u ilib riu m expression from Figure 5.2b is : (Tst + Tsb^Afc + TG = p; *h ere Afc = Lc x Wavg, and I G = g e o te x tile te n s ile fo rc e. When the applied h o rizo n tal load P reaches it s u ltim a te v a lu e, f u ll in te rfa c e shearing resistan ce gets m obilized along the to ta l surface area o f the g e o te x tile, and the g e o te x tile sample moves as a whole. At th is p o in t i t is reasonable to assume a uniform shear stress d is trib u tio n along the in te rfa c e due to the re o rie n ta tio n o f the s o il p a r tic le s. Tgj. = Tsb. I f the support and cover m a te ria ls are the same, then The galvanized sheet metal had very smooth su rfaces, and the shear stresses developed along them due to the normal pressures were assumed to be very small compared to the shear stresses developed on the g e o te x tile -s o il in te rfa c e. T h e re fo re, the m obilized shear stresses along the sheet m e ta l-s o il in te rfa c e were neglected. Equivalent te n s ile stresses ( o j) under various normal pressures (a n) were obtained by d iv id in g the g e o te x tile s tre tc h -o u t load (P) by the cro ss-sectio n al area o f the g e o te x tile. Equivalent te n s ile stresses were p lo tte d a t 5% s tra in increments fo r the sake o f c l a r it y ; but the

61 s tre s s -s tra in curves themselves were drawn using in term ed iate points as w e ll. 48 Woven G eotextiles A ll woven g e o te x tile s m aintained a constant specimen w idth during horizontal loading in the d ir e c t shear device w ithout s o il in the sample box (Fig ure 5.1 ). T h e re fo re, s tre s s -s tra in curves were d e te r mined fo r constant cross-section a t a ll stress le v e ls. P o ly f ilt e r X The s tre s s -s tra in curves fo r P o ly f ilt e r X are shown in Figures 5.3, 5.4, 5.5 and 5.6. I t can be seen from these fig u re s th a t a ll o f the g e o te x tile s tre s s -s tra in curves e x h ib it an i n i t i a l lin e a r portio n u n til approxim ately 0.5 percent e. Furtherm ore, as was expected, equivalen t te n s ile stresses increased w ith increasing normal pressure a t a ll s tra in le v e ls. E ffe c t o f Dry Sand-Dry Sand In te rfa c e ( 5-5 ). When both cover and support m a te ria ls were dry #30 Ottawa sand, high shear stresses were m obilized along the g e o te x tile -s o il in te rfa c e due to the a p p lic a tio n o f normal pressures. This is shown in Figure 5.3 where a s i g n i f i cant increase in the eq u ivalen t te n s ile stress can be noted fo r even a normal stress o f 0.5 t s f as compared to the unconfined specimen. The higher the normal pressure, the higher the equivalen t te n s ile stress a t the same s tra in le v e l. To develop an equation fo r the s tre s s -s tra in curves and the tangent modulus as a functio n o f the confinin g pressure, a procedure from

62 49 O 4 t s f 2 t s f O 1 t s f 1 /2 t s f O 0 t s f (te n s ile s trength ) S tra in x 10 ( in / in ) Figure 5.3. S tre s s -s tra in curves fo r P o ly f ilt e r X fa b r ic (support and cover m a te ria l = dry #30 Ottawa sand).

63 50 H 4000 O A O 4 t s f 2 t s f 1 t s f 1 /2 t s f O 0 t s f (te n s ile stren g th ) S tra in x 10"^ ( in / in ) Figure 5.4. S tre s s -s tra in curves fo r P o ly f ilt e r X fa b r ic (support and cover m ateria l = wet #30 Ottawa sand).

64 51 q E t s f 2 t s f 1 t s f 1 /2 t s f O 0 t s f (te n s ile stren g th ) S tra in x 10 ( in / in ) Figure 5.5. S tre s s -s tra in curves fo r P o ly f ilt e r X fa b r ic (cover m ateria l = dry #30 Ottawa sand; support m a te ria l = fin e g ra v e l).

65 t s f 2 t s f 1 t s f O 1 /2 t s f O 0 t s f (te n s ile s trength ) S tra in x 10 ( in / in ) Figure 5.6. S tre s s -s tra in curves fo r P o ly f ilt e r X fa b r ic (support and cover m ateria l = dry fin e g r a v e l).

66 53 Duncan and Chang (1970) was fo llo w ed. The i n i t i a l tangent moduli (E^), o f the s tre s s -s tra in curves under the various normal pressures, were computed and p lo tte d versus t h e ir corresponding normal pressures (a n ), as shown in Figure 5.7. In a d d itio n, th e secand moduli (Esec) j o f the s tre s s -s tra in curves a t 20 percent e, were computed and p lo tte d versus t h e ir corresponding normal pressures. Two s tr a ig h t lin e s were obtained: one fo r E. and one fo r Esec2Q' These s tra ig h t lin e s in d ic a te th a t E- and Esec2Q fo r the g e o te x tile s increase lin e a r ly on lo g -lo g paper w ith increasing normal pressures. I f the slope o f the E^ lin e and it s y - in te rc e p t are c a lle d q and k, re s p e c tiv e ly, the fo llo w in g equation can be w ritte n : log E. = q log a n + log k log Ej - q log a n = log k log Ei - lo g (a n ) q = log k Ei log - (on) q = log k Ei = k (a n) q (5.1 ) To obtain a b e tte r d e fin itio n o f E^, a p lo t o f versus e fo r 1 T x\~ ^ t s f and a n = 4 t s f o f P o ly f ilt e r X, under the confinement o f dry #30 Ottawa sand, is presented in Figure 5.8. Inverse o f -7 - a t the in t e r - ctt cept gives the i n i t i a l tangent modulus fo r it s corresponding normal pres- sure. 1 For normal pressures between ^ t s f and 4 t s f, lin e a r in te rp o la tio n

67 54 loooooq : : Figure 5.7. Log versus log c n fo r P o ly f ilt e r X fa b r ic (cover and support m a te ria l = dry #30 Ottawa sand).

68 55 between the s tra ig h t lin e s shown in Figure 5.8 is v a lid to fin d the value. A break in the s tr a ig h t lin e curve e x is ts a t small s tra in le v e ls fo r both normal pressures. T h e re fo re, each curve is approximated by two s tra ig h t lin e segments w ith d iffe r e n t slopes and y -in te r c e p ts. These slopes and y -in te rc e p ts o f the s tr a ig h t lin e segments are represented in Table 5.1. The general equation o f any s tra ig h t lin e on the axes shown is : ~ ~ - m e + b T (5.2 ) where m and b are the slope and y -in te r c e p t, re s p e c tiv e ly. Solving equation 5.2 fo r O j, gives: at ~ me + b (5.3 ) Equation 5.3, th e r e fo r e, is the equation fo r the s tre s s -s tra in curves o f Figure 5.3. The tangent modulus (Et ) is the d e riv a tiv e o f Oj in Equation 5.3 w ith respect to e : da Ṫ de me + b (me + b ) me (me + by (5.4 ) A general equation fo r the tangent modulus th a t re la te s i t to the normal pressures, s tr a in s, and the slopes and y -in te rc e p ts o f Figures 5.7 and 5.8 is derived as fo llo w s : T e me + b

69 56 O 1 /2 t s f # 4 t s f e x 10 ( in / in ) Figure 5.8. e/c-j. versus e f o r P o ly f ilt e r X fa b r ic (support and cover m a te ria l = dry #30 Ottawa san d).

70 57 Table 5.1. Slope (m) and y -in te r c e p t (b) values fo r the s tra ig h t lin e s o f Figures 5.8 and 5.22 Fabric an ( t s f ) E ( in ^ /lb ) ( in ^ /lb ) 0 < e < x 10"5.9 x 10' 5 1 /2 P o ly f ilt e r X.075 < e < x 10' x < e < x 10"5.2 x 10" < e < x 10"5.7 x 10"5 0 < e < x 10' x 10"5 1 /2.025 < c < x 10"3 4 x 10" 5 M ira fi 140S.07 < e < x 10"3 5.6 x 10" 5 0 < e < x 10" x 10' < e < x 10' x 10" 5

71 58 ' de ' (me + b) 2 a t e = 0, Et = E. E^ = p but Ei = k(an ) q by Equation 5.1. b = r r 3 r r r ^ = ^ (on r q i k(on)' and E^ = t " ( [ ( o n) - q + me) 2 (5.5 ) Equation 5.5 re la te s the mechanical p ro p e rties o f the g e o te x tile s w ith the normal pressures under which the g e o te x tile is embedded; th e r e fo r e, i t is useful fo r design analysis in the s o il-g e o te x tile re in fo rc e ment system in which the g e o te x tile becomes an in te ra c tiv e s tre s s c a rry in g component o f the system. E ffe c t o f M oisture Content. The fib e rs used to make fa b ric s are g e n e ra lly hydrophobic and, th e re fo re, r e la t iv e ly in s e n s itiv e to m oisture reg ain. The m oisture regain o f polypropylene is n e g lig ib le and th a t o f p o lyester less than 0.5 percent (K asw ell, 1963). This im plies th a t the bonding mechanism among fib e rs is the c r i t i c a l fe a tu re o f fa b r ic performance in p a r t ia lly saturated o r f u l l y saturated conditions (Koerner e t a l., 1980). The te n s ile strength fo r P o ly f ilt e r X tested w ith wet #30 Ottawa sand as cover and support m a te ria ls under zero normal pressure, was the same as fo r the dry case. For wet c o n d itio n s, however, some w ater was

72 retain ed on the g e o te x tile -s o il in te rfa c e during te s tin g because o f the 59 low p e rm e a b ility and rough surface o f P o ly f ilt e r X fa b r ic. This wet g e o te x tile -s o il in te rfa c e caused th e g e o te x tile to s lip s lig h t ly. Thus shear stresses m obilized on the g e o te x tile in te rfa c e decreased w ith a corresponding reduction in the e q u ivalen t te n s ile stresses. The equivale n t te n s ile stress red u c tio n, a t 25 percent e, was ap p ro xin ately 35 percent as shown in Figure 5.9. E ffe c t o f Sand-Gravel In te rfa c e (S -G ). A p lo t o f the s tre s s - s tra in curves fo r P o ly f ilt e r X f a b r ic, under the confinement o f dry #30 Ottawa sand as cover m ateria l and dry fin e gravel as support m ateria l is presented in Figure 5.5. Since th ere is less surface contact on the g e o te x tile -g ra v e l in te rfa c e than on the g e o te x tile -s a n d in te rfa c e, less shear stress is m obilized along the g e o te x tile -g ra v e l in te rfa c e than along the g e o te x tile -s a n d in te rfa c e. The net re s u lt is a reduction in the eq u ivalen t te n s ile stresses. E ffe c t o f G ravel-g ravel In te rfa c e (G -G ). S tre s s -s tra in curves fo r P o ly f ilt e r X f a b r ic, under the confinement o f dry fin e gravel as support and cover m a te ria ls, are shown in Figure 5.6. The observed s tre s s -s tra in re la tio n s h ip suggests th a t the gravel touching the rough surface o f the P o ly f ilt e r X fa b ric i n i t i a l l y moved h o riz o n ta lly along w ith the fa b ric when i t was p u lle d. This in te rfa c e gravel movement passed by a p o in t where the gravel p a rtic le s in the cover and support m a te ria ls got on top o f each o th e r, i. e., t h e ir centers la y on one v e r t i cal s tra ig h t lin e. Im m ediately, th e re was a reduction in the surface

73 60 1 /2 t s f O O Dry In te rfa c e Wet In te rfa c e T e n s ile Strength S tra in x 10 ( in / in ) Figure 5.9. S tre s s -s tra in curves fo r P o ly f ilt e r X fa b ric (support and cover m ateria l = #30 Ottawa sand).

74 61 contact area a t the g e o te x tile -s o il in te rfa c e which caused a reduction in the m obilized shear stresses and th e re fo re, a reduction in the eq u i v a le n t te n s ile stresses. As the p u ll-o u t te s t continued under the applied normal pressure, the confining m ateria l was d e n s ify in g, causing the gravel p a rtic le s to in te rlo c k a t the in te rfa c e. This re s u lte d in an increase o f the surface contact area and a consequent increase in the m obilized shear stresses. A corresponding increase in the e q u ivalen t te n s ile stresses also occurred. For high normal pressures (a n = 4 t s f ), the cover and support m a te ria ls were d e n s ifie d already before s ta rtin g the p u ll-o u t te s t. T h e re fo re, the surface contact area a t the g e o te x tile - s o il in te rfa c e was almost constant during te s tin g due to gravel p a rtic le s continuous in te rlo c k in g under the high normal pressure. The equivalen t te n s ile stresses fo r P o ly f ilt e r X under 4 t s f normal pressure were in creasing s te a d ily and smoothly during horizo n tal lo ad in g. Figure 5.6 in d ic ates th a t the tangent modulus is almost constant f o r a ll normal pressures a t about 20% s tr a in. Comparison Between Various Combinations o f G e o te x tile In te rfa c e M a te ria ls and P o ly f ilt e r X. Plots o f s tre s s -s tra in curves fo r P o ly f ilt e r X fa b ric and sand-sand in te rfa c e (S -S ), sand-gravel in te rfa c e (S -G ), and g ra v e l-g ra v e l in te rfa c e (G -G ), under confinement o f normal pressures \ o f j t s f and 4 t s f are shown in Figures 5.10 and 5.1 1, re s p e c tiv e ly. Under ^ t s f normal pressure, the m o b iliza tio n o f shear stresses on the g e o te x tile faces was almost the same fo r the th ree aforementioned geot e x t ile in te rfa c e s, e s p e c ia lly a t low s tra in le v e ls. Figure 5.11 shows th a t under 4 t s f normal pressure, the g e o te x tile sand-sand in te rfa c e m obilized the highest shearing stresses along the g e o te x tile s faces,

75 62 Equivalent T en sile Stress ( p s i) S-S In te rfa c e S-G In te rfa c e A G-G In te rfa c e O T e n s ile Strength S tra in x 10" 3 ( in / in ) Figure S tre s s -s tra in curves fo r P o ly f ilt e r X f a b r ic, under 1 /2 t s f normal pressure and various support and cover com binations.

76 63 S-S In te rfa c e # S-G In te rfa c e A G-G In te rfa c e O T e n s ile Strength S tra in x 10" 3 ( i n / i n ) Figure S tre s s -s tra in curves fo r P o ly f ilt e r X fa b ric under 4 t s f normal pressure fo r various combinations o f cover and support m a te ria ls.

77 64 re s u ltin g in the highest eq u ivalen t te n s ile stresses. The lowest shear stresses were m obilized along the g e o te x tile g ra v e l-g ra v e l in te rfa c e. M ira fi 100X and M ira fi 500X S tre s s -s tra in curves fo r M ir a fi 100X and M ira fi 500X woven fa b ric s are shown in Figures 5.1 2, 5.1 3, 5.14 and 5.15 under the confinement o f dry #30 Ottawa sand as cover and support m a te ria ls. The stru ctu res o f M ira fi 100X and M ira fi 500X are q u ite d iffe r e n t from th a t o f the P o ly f ilt e r X. T h e ir fib e rs are woven in such a way th a t they might be stronger in one d ire c tio n than in the perpendicular cross d ire c tio n. Schematic rep resen tatio n o f an exaggerated cro ss-sectio n fo r M ir a fi 100X and 500X is shown in Figure When the h o rizo n tal fo rce P is applied on the filam ents in one d ir e c tio n, the g e o te x tile f i r s t tends to f la t t e n o u t. Then, immediately a f t e r the p u lle d filam ents become h o riz o n ta lly s tr a ig h t, the g e o te x tile begins to s lip, re s u ltin g in reduction o f eq u iv a le n t te n s ile stresses. Soon afte rw ard s, the shearing stresses become m obilized along the in t e r face due to the rough surface o f the g e o te x tile, re s u ltin g in an increase in the equivalen t te n s ile stresses. Under zero normal pressure, the te n s ile stresses increase to an u ltim a te value o f about 10 percent e, then they s t a r t decreasing s lig h tly as the s tra in increases.

78 t s f 2 t s f 1 t s f 1 /2 t s f 0 t s f (te n s ile stren g th ) S tra in x 10"^ ( in / in ) F ig u re S tr e s s - s tr a in curves f o r M ir a fi 100X f a b r ic along g ra in s (s u p p o rt and co ve r m a te ria l = d ry #30 Ottawa sand).

79 66 4 t s f 2 t s f 1 t s f 1 /2 t s f O 0 t s f (te n s ile stren g th ) S tra in x lo '3 ( in / in ) F ig u re S tr e s s - s tr a in curves f o r M ir a fi 100X f a b r ic across g ra in s (s u p p o rt and cover m a te ria l = d ry #30 Ottawa sand).

80 in o in in Q) u. 4-> CO in ccd 4-> CCD > 1000 =3 cr LU S tra in x 10 ( in / in ) F ig u re S tr e s s - s tr a in curves f o r M ir a fi 500X f a b r ic along g ra in s (s u p p o rt and co ve r m a te ria l = d ry #30 Ottawa sand).

81 68 4 t s f 2 t s f 1 t s f 1 /2 t s f 0 t s f (te n s ile stren g th ) S tra in x 10"^ ( in / in ) F ig u re S tr e s s - s tr a in curves f o r M ir a fi 500X f a b r ic across g ra in s (s u p p o rt and co ve r m a te ria l = d ry #30 Ottawa sand).

82 69 Figure S tru ctu re o f M ir a fi 100X and M ir a fi 500X. Nonwoven G e o textiles Nonwoven g e o te x tile s have smooth surfaces as compared to those o f the woven g e o te x tile s. During h o rizo n tal lo a d in g, the width o f a ll the nonwoven samples o f the g e o te x tile s dim inished and subsequently fa ile d by necking down (Fig ure 5.1 ). M ira fi 140S The te s tin g procedure performed fo r P o ly f ilt e r X woven fa b ric was also follow ed in te s tin g M ir a fi 140S nonwoven f a b r ic. S tre s s -s tra in curves fo r M ir a fi 140S are shown in Figures 5.1 7, 5.1 8, 5.19 and As in d ic ated in these fig u re s, the equivalen t te n s ile stresses increased w ith increasing normal pressure a t a ll s tra in le v e ls., E ffe c t o f Dry Sand-Dry Sand In te rfa c e (S -S ). The eq u ivalen t te n s ile stress versus s tra in re la tio n s h ip fo r M ir a fi 140S w ith both cover and support m a te ria ls being dry #30 Ottawa sand are shown in Figure 5.17 fo r various normal stresses. As in d ic a te d in the fig u r e, the higher the normal pressure, the higher the eq u ivalen t te n s ile stress a t the same s tra in le v e l.

83 <n o. to to <us- 4-3 CO to c CD 4-3 C CD fo > Z3 cr LlJ 4 t s f ; 2 t s f 1 t s f 1 /2 t s f 0 t s f (te n s ile strength ) S tra in x 10 ( in / in ) Figure S tre s s -s tra in curves fo r M ir a fi 140S fa b ric (support and cover m ateria l = dry #30 Ottawa sand).

84 71 Figure S tre s s -s tra in curves fo r M ir a fi 140S fa b ric (support and cover m ateria l = wet #30 Ottawa sand).

85 72 F ig u re S tr e s s - s tr a in curves f o r M ir a fi 140S f a b r ic (s u p p o rt m a te ria l = d ry f in e g r a v e l; cover m a te ria l = d ry #30 Ottawa s a n d ).

86 S tra in x 10"^ ( in / in ) Figure S tre s s -s tra in curves fo r M ir a fi 140S fa b r ic (support and cover m ateria l = dry fin e g ra v e l).

87 74 The same procedure was follow ed fo r M ir a fi 140S as was follow ed fo r P o ly f ilt e r X to e s ta b lis h a re la tio n s h ip between the tangent modulus and confinin g pressure (Equation 5.5 ). Log E versus log an fo r M ir a fi. 140S' dry sand-sand in te r fa c e is presented in F igure The -7- versus at E p lo t is presented in Figure Table 5.1 gives the slope (m) and y -in te rc e p t (b) values fo r the s tr a ig h t lin e segments o f Figure As in d icated p re v io u s ly. Equations 5.1, 5.2, 5.3, 5.4, and 5.5 derived fo r P o ly f ilt e r X woven fa b r ic are also a p p licab le fo r M ira fi 140S nonwoven f a b r ic. As a num erical example using Equation 5.5 : n = 4 tsf = psi q =.443 k = 16,050 psi Figure = 95,000 psi J E =.15 m =.5 x 10-3 n J Figure 2.25 i <V 1 16,050 (5 5.55) " * 443 [F (an)"q + me]2 ETeToBo*55-55) " *5 x io"3(-15)]2 Et = 1,437 psi which is the same value th a t could be obtained by u t iliz in g Figure

88 !==S! n (psi) Figure Log E- versus log a fo r M ir a fi 1405 (cover and support m ateria l = "dry #30 Ottawa sand).

89 76 1 /2 t s f 4 t s f e x 10 ( in / in ) F ig u re e / a j versus e f o r M ir a fi 140S f a b r ic (s u p p o rt and co ve r m a te ria l = d ry #30 Ottawa sa n d ).

90 77 E ffe c t o f M oisture Content. The fib e rs used to make M ir a fi 140S fa b ric are hydrophobic and, th e re fo re, r e la t iv e ly in s e n s itiv e to m oisture reg ain. The te n s ile strength fo r M ir a fi 140S fa b ric tested w ith wet #30 Ottawa sand as cover and support m a te r ia l, under zero normal pressure, was the same as fo r the dry case. The wet specimens y ie ld e d higher equivalen t te n s ile stresses under increased normal pressures. This may be due to w ater in the s o il forming in te rg ra n u la r bonds th a t increase e ffe c tiv e stress and r e s u lt in den sifyin g the s o il. The equivalen t te n s ile stress increase due to the m oisture content fo r M ir a fi 1405 is in d ic ated in Figure 5.23 under 1/2 t s f normal pressure. E ffe c t o f Sand-Gravel In te rfa c e (S -G ). A p lo t o f the s tre s s - s tra in curves fo r M ir a fi 1405 f a b r ic, under the confinement o f dry #30 Ottawa sand as cover m ateria l and dry fin e gravel as support m a te r ia l, is presented in Figure Since th ere is less surface contact on the g e o te x tile -g ra v e l in te rfa c e, less shear stresses were m obilized along the g e o te x tile -g ra v e l in te rfa c e than along the g e o te x tile -s a n d in te rfa c e. The net r e s u lt is a reduction in the equivalen t te n s ile stresses. E ffe c t o f G ravel-g ravel In te rfa c e (G -G ). S tre s s -s tra in curves fo r M ir a fi 140S f a b r ic, under the confinement o f dry fin e gravel as support and cover m a te r ia l, are shown in Figure Due to the smooth surface o f M ir a fi 140S, the fa b r ic was s lid in g along the in te rfa c e under the applied normal pressure. A steady increase in the e q u ivalen t te n s ile stresses w ith increasing s tra in is observed and is a ttr ib u te d to th e f u l l and almost uniform m o b iliza tio n o f shear stresses on the in te rfa c e. The

91 78 1 /2 t s f A Dry In te rfa c e Wet In te rfa c e T en sile Strength Figure S tre s s -s tra in curves fo r M ir a fi 140S fa b r ic (cover and support m ateria l = #30 Ottawa sand).

92 79 s tre s s -s tra in curves have n e a rly constant tangent m oduli, a f t e r about 20% c regardless o f the applied normal pressures. Comparison Between Various Combinations o f G e o te x tile In te rfa c e M a te ria ls and M ira fi 140S. P lots o f s tre s s -s tra in curves f o r M ir a fi 140S fa b r ic and sand-sand in te rfa c e (S -S ), sand-gravel in te rfa c e (S -G ), and g ra v e l-g ra v e l in te rfa c e (G-G) under confinement o f 1 /2 t s f and 4 t s f normal pressures are shown in Figures 5.24 and 5.2 5, re s p e c tiv e ly. The g e o te x tile sand-sand in te rfa c e m obilized the highest shearing stresses along the g e o te x tile surfaces, re s u ltin g in the highest e q u ivalen t te n s ile stresses under the applied normal pressures. G o e te x tile g ra v e l- gravel in te rfa c e m obilized the lowest shearing stresses due to small contact surface area between the gravel p a rtic le s and the g e o te x tile. This y ie ld e d low eq u ivalen t te n s ile stresses. G e o te x tile sand-gravel in te rfa c e y ie ld e d equivalen t te n s ile stresses in between those y ie ld e d by the g e o te x tile sand-sand in te rfa c e and g e o te x tile g ra v e l-g ra v e l in te rfa c e. Typar 3601 and Bidim C-34 Typar 3601 and Bidim C-34 are smooth woven fa b r ic s. T h e ir samples f a ile d by necking down as the fa b r ic was p u lle d (Fig ure 5.1 ). The s tre s s -s tra in curves fo r Typar 3601 and Bidim C-34 are shown in Figures 5.26 and 5.2 7, re s p e c tiv e ly. These curves f o r each fa b r ic have almost id e n tic a l tangent moduli a f t e r about 20% e, regardless o f the various normal pressures. As in d ic ated p re v io u s ly, i t is f e l t th a t th is is due to the f u ll and even m o b iliza tio n o f a l l the shearing stresses on the g e o te x tile -s o il in te rfa c e s o f r e la t iv e ly smooth g e o te x tile s.

93 80 A O S-S In te rfa c e S-G In te rfa c e G-G In te rfa c e T e n s ile Strength S tra in x 10~3 ( in / in ) Figure S tre s s -s tra in curves fo r M ir a fi 140S fa b r ic fo r various combinations o f g e o te x tile -s o il in te rfa c e under 1 /2 t s f normal pressure.

94 to Q. / / / ^ J 00 <D l/> C h- g 800 CD fo > r- 3 cr LU 400 f f / / f A S-S In te rfa c e a D S-G In te rfa c e II s ' O G-G In te rfa c e «y Z # T e n s ile Strength r i i i I i S tra in x 10"^ ( in / in ) Figure 5.25 S tre s s -s tra in curves f o r M ir a fi 140S fa b ric fo r various combinations o f g e o te x tile -s o il in te rfa c e under 4 t s f normal pressure.

95 S t s f 2 t s f 1 t s f 1 /2 t s f 0 t s f (te n s ile stren g th ) S tra in x 10"3 ( in / in ) Figure S tre s s -s tra in curves fo r Typar 3601 fa b r ic (support and cover m ateria l = dry #30 Ottawa sand).

96 83 4 t s f 2 t s f 1 t s f 1 /2 t s f O 0 t s f (te n s ile s trength ) S tra in x 10 ( in / in ) Figure S tre s s -s tra in curves fo r Bidim C-34 fa b r ic (support and cover m ateria l = dry #30 Ottawa san d).

97 CHAPTER 6 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS Summary The main purpose o f th is research was to study the e ffe c t o f confinin g pressure on te n s ile strength c h a ra c te ris tic s o f g e o te x tile s. This has d ir e c t a p p lic a tio n to the eq u ivalen t te n s ile strength and type o f f a ilu r e o f the g e o te x tile s when embedded in the ground. A special sample box was designed to perform the te n s ile te s ts o f the g e o te x tile s. Three d iffe r e n t combinations o f support and cover m a te ria ls were used fo r each o f the th ree d iffe r e n t types o f woven and nonwoven g e o te x tile s. The e ffe c ts o f S-S in te rfa c e on equivalen t te n s ile strength were in v e s tig a te d fo r a ll the kinds o f g e o te x tile s te s te d. Furtherm ore, the e ffe c t o f m oisture co n ten t, S-G in te rfa c e, and G-G in te rfa c e were in v e s tig a te d fo r one kind o f each type o f g e o te x tile (woven and nonwoven). Conclusions The re s u lts o f the aforementioned experim ental te s ts can be summarized as fo llo w s: 1. Woven g e o te x tile s m aintained a constant la te r a l w idth during h o rizo n tal s tre tc h in g. Nonwoven g e o te x tile s f a ile d by necking. 84

98 85 2. The higher the normal pressure, the higher the m obilized shearing stresses on the g e o te x tile in te rfa c e and the g re a te r the re s u ltin g equivalen t te n s ile s tre s s. 3. D iffe re n t kinds o f in te rfa c e s w ith the same g e o te x tile s resu lted in s ig n ific a n t d iffe re n c e s in the eq u iv a le n t te n s ile stress fo r the woven g e o te x tile due to it s rough surface. On the o th er hand, only a s lig h t d iffe re n c e in the eq u ivalen t te n s ile stress was observed fo r the nonwoven g e o te x tile s due to it s smooth surface. 4. The fo llo w in g e ffe c ts were noted fo r wet conditions and under various normal pressures: P o ly f ilt e r X woven g e o te x tile y ie ld e d lower eq u ivalen t te n s ile stresses than fo r the dry cases due to it s low p e rm e a b ility and the w ater re ta in e d on it s rough su rface; M ir a fi 140S nonwoven g e o te x tile y ie ld e d higher e q u ivalen t te n s ile stresse s than f o r the dry cases due to the in crease in th e e f f e c tiv e stresses re s u ltin g from the w ater c a p illa r y tension e f f e c t s. 5. Equations fo r the i n i t i a l tangent modulus, equivalen t te n s ile s tre s s, and the tangent modulus o f various s tra in le v e ls as a fu n ctio n o f the normal pressure were derived from one woven and one nonwoven g e o te x tile. These equations were derived fo r both woven and nonwoven g e o te x tile s w ith an S-S in te rfa c e. The general form o f the equation is ap p lic a b le to o th e r g e o fa b ric -s o il comb in a tio n s. 6. The i n i t i a l tangent modulus fo r the g e o te x tile s v a rie d w ith the normal pressure and i t is d iffe r e n t from the i n i t i a l tangent

99 86 modulus o btained from te s ts w ith o u t confinem ent. This is contr a r y to the assumption made by Sanan (1980) in his study o f the e ffe c t o f g e o te x tile s on stress atte n u a tio n in buried c u l v e rts. He assumed th a t E. fo r g e o te x tile s is constant whether the g e o te x tile is confined or unconfined. The fa c t th a t i t is n o t, as shown by th is research, may a ffe c t the re s u lts o f th a t study. This research was not meant to suggest th a t any o f the geotext i l e s studied is b e tte r than any o f the o th ers. The choice o f any kind o f g e o te x tile fo r geotechnical engineering a p p lic a tio n s, should be made independently according to the f i e l d s itu a tio n s and eng ineering judgm ent. Recommendations Most o f the g e o te x tile s are used fo r s o il reinfo rcem ent. Thus, the g e o te x tile strength is o f prime im portance, and it s conventional strength te s tin g is w ell estab lish ed. However, the strength parameters o f in te re s t in the geotechnical use o f g e o te x tile s is d iffe r e n t from those obtained from conventional te s tin g in a number o f respects. For example, s tra in rates are often very low when buried g e o te x tile s are loaded. During lo a d in g, necking o f the g e o te x tile may occur; conseq u e n tly, te n s ile stresses may change w ithout la rg e increase in load. The method o f stress a p p lic a tio n may also vary during the l i f e o f the system since the d ire c tio n o f stress a p p lic a tio n is o ften not always known. M oisture conditions also may vary from dry to s a tu ra te d. Thus i t is im portant to examine the e ffe c ts o f a ll o f these v a ria b le s on the

100 behavior o f buried g e o te x tile s, regardless o f what th e s p e c ific geotechnical a p p lic a tio n may be. Many o f these in v e s tig a tio n s are best conducted by f u ll- s c a le f ie l d te s ts.

101 REFERENCES B assett, R. H. and N. C. Last. "R einforcing Earth Below Footings and Embankments," Proceedings, Symposium on Earth Reinforcem ent, ASCE, A p ril 1978, pp B e ll, J. R. "In tro d u c tio n to G eo textiles fo r S oil Improvement," ASCE Convention and E xpositio n, A p ril 1980, pp C o llio s. A., P. Delmas, J. P. Gourc and J. P. Giroud. "Experiments on S oil Reinforcement w ith G e o te x tile s," ASCE Convention and E xposition, A p ril 1980, pp , 67. Commercial d is p la y s published by th e g e o te x tile m anufacturers in Bidim: Montanso T e x tile s Company, Nonwoven Business Group G4WC, 800 N. Lindbergh B lv d., S t. Louis, Missouri M ir a f i : Celanese Fibers M arketing Company, 1211 Avenue o f the Americas, New York, New York P o ly f ilt e r X: Carthage M ills, C in c in n a ti, Ohio Typar: Watkins T ra c to r and Supply C o., 501 S. P a c ific Avenue, P. 0. Box 660, Kelso, Washington Del mas, P., J. P. Gourc and 0. P. G iroud. "Analyse Experim entale de L 'in te ra c tio n Mechanique S o l-g e o te x tile," Compte-Redus Collogue In te rn a tio n a l Renforcement des S o ls, P a ris, 1979, pp Duncan, J. M. and C. Y. Chang. "Nonlinear Analysis o f Stress and S tra in in S o ils," Journal o f the S o il Mechanics and Foundations D iv is io n, ASCE, V o l. 96, No. SMS, Proceedings, paper 7513, September 1970, pp Iw a s k i, K. and S. Watanabe. "Reinforcement o f Railway Embankments in Japan," Proceedings, Symposium on Earth Reinforcem ent, ASCE, A p ril 1978, pp K a s w e ll, E. R. Education Departm ent, Man-Made F ib e r Products A ssociatio n, I n c., 1150 Seventeenth St., N.W., Washington, D.C., Koerner, R. M., J. L. R osenfarb, W. W. Dougherty and J. J. M celroy. "S tress-s train -T im e Behavior o f G e o te x tile s," ASCE Convention and E xpositio n, A p ril 1980, pp. 36. Potyondy, J. G. "Skin F ric tio n Between Various S o ils and Construction M a te ria ls," Geotechnique, V o l. 11, No. 4, 1961, pp

102 Salomone, W. G., E. Boutrup, R. D. H o ltz, W. D. Kovacs and C. D. S u tton. "Fabric Reinforcement Designed Against P u llo u t," ASCE Convention and E xpositio n, A p ril 1980, pp Sanan,B. K. "An Evaluation o f the E ffe c ts o f Geofabrics on Stresses and Displacements in Buried C u lv e rts," Ph.D. D is s e rta tio n, U n iv e rs ity o f A rizona, Tucson, A rizona, 1980, pp

103 96 g