Compaction of Sand-Processed Clay Soil Mixtures

8/13/2019 Compaction of Sand-Processed Clay Soil Mixtures

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Jenni f er L . H owel l 1 Char les D. Shackel for d 2 N abi l H . Amer 3 and Ros lyn T. S t er n 4

Compaction of Sand Processed Clay Soil Mixtures

REFERENCE Howell, J. L., Shackelford, C. D., Am er, N. H., andStem, R. T. Compa ction of Sand-Processed Clay Soil Mixtu resGeotechnical Testing Journa l GTJODJ, Vol. 20, No. 4, December1997, pp. 443--458.

ABST RAC T: The effects o f type of processed clay soil, curing period,and mixing procedure on laboratory compaction of sand-attapulgite

clay (S-AC), sand-granular bentonite (S-GB), sand-powdery bentonite(S-PB), and sand-attapulgite clay-granular bentonite (S-AC-GB) m ix-tures are evaluated. Compaction is evaluated for total clay soil contentsof 10, 15, and 20% . Different trends in optimum water content,Woptand maximum dry unit w eight, Tamax, versus clay soil content amongthe S-AC, S-GB, and S-PB m ixtures are attributed, in part, to (l ) thegreater water sorptivity and low er swelling potential of attapulgite clayrelative to the bentonites, (2) the larger particle sizes of the granularbentonite in the air-dried condition relative to the powdery bentonite,and (3) the possible correlation between the Wopt and the plasticityindex o f the sand-bentonite mixtures. The Awopt values and ATdmaxvalues resulting from one-day versus seven-day curing periods beforecompaction of the S-GB and S-PB mixtures are --0 .5 percentage pointsand --


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GEOTECHNICAL TESTING JOURNAL

a t e r i a l s

Soi l s

The so i l s used as mix tu re cons t i tuen t ma te r i a l s in th i s s tudy a rea t t apu lg i t e c l ay, g ranu la r ben ton i t e , powdery ben ton i t e , and sand .

A q u a l i t a t iv e c o m p a r i s o n o f t h e p r o p e r t i e s o f a t t a p u l g it e c l a y a n db e n t o n i t e i s p r o v i d e d i n Ta b l e 1 . T h e p h y s i c a l a n d c h e m i c a l p r o p e r -t i e s o f the cons t i tuen t ma te r i a l s used in the so i l mix tu res in th i ss tudy a re summ ar ized in Tab les 2 and 3 , r e spec t ive ly. The p roce -

TABLE t--Qu alitativ e comparison o f attapulgite and bentonite claysoils after Tobin and Wild 1986).

Clay Soil Characteristic

Type of Clay Soil

Attapulgite Bentonite

Principal mineral attapulgiteCry stal structure chainParticle shape needleSurface area highSwell potential lowCation exchange capacity lowEffect of electro lytes slightSorptivity high

montmorillonitethree-layer sheet

platemedium

highhigh

flocculatesmedium

d u r e s u s e d t o m e a s u r e t h e s o i l c h e m i c a l p r o p e r t i e s a r e d e s c r ib e db y S h a c k e l f o r d a n d R e d m o n d ( 1 9 9 5 ) .

In genera l , a t t apu lg i t e c rys ta l s a re need le - l ike , r e su l t ing in aggre -ga tes tha t fo rm a hay s t ack s t ruc tu re . The a t t r ac t ive fo rcesbe tween the need les wi th in a pa r t i c l e a re cons ide rab le , and the re -fo re a t t apu lg i t e i s no t pa r t i cu la r ly suscep t ib le to swe l l ing . How ever,a t t apu lg i t e i s a h igh ly so rp t ive mate r i a l in t e rms o f absorp t ion o fw a t e r i n t o t h e c h a n n e l s b e t w e e n t h e c r y s t a ls . A t t a p u l g i t e c la y a l s oappea rs to be s t ab le in h igh concen t ra t ions o f e l ec t ro ly tes and ,the re fo re , i s no t a s su scep t ib le a s the p la te - l ike c l ay minera l s tod r a m a t i c c h a n g e s i n h y d r a u l i c c o n d u c t i v i ty a f t e r e x p o s u r e t o l i q u i dwas te (Tob in and W i ld 1986) . As a r e su l t , a t tapu lg i t e c l ay ma ybe use d as a so i l add i t ive to he lp s t ab i l i ze an o the rwise uns tab leso i l (Brod er ick and Dan ie l 1990). How ever, s ince the h igh swe l l ingp o t e n t i a l e v i d e n t i n s o d i u m b e n t o n i t e i s n o t e v i d e n t i n a t t a p u l g i tec l a y d u e t o t h e d i f f e r e n c e i n m i n e r a l o g i c a l c o m p o s i t i o n o f t h e s o i l ,the p r ima ry concern wi th the use o f a t t apu lg i t e c l ay as a l ine rmate r i a l i s the ab i l i ty to ach ieve a r e l a t ive ly low hyd rau l i c conduc-t i v i t y w h e n p e r m e a t e d w i t h w a t e r ( H o w e l l a n d S h a c k e l f o r d 1 9 9 7 ).

P a n i c l e - s i z e d i s t r ib u t i o n s o f t h e s o i l c o n s t i t u e n ts a r e s h o w n i nF i g . 1 . F o r t h e c l a y s o i ls , th e r e s u l t s o f b o t h h y d r o m e t e r a n a l y s e s( A S T M D 4 2 1 ) 5 a n d m e c h a n i c a l s i e v e a n a l y s e s ( A S T M D 4 2 2 ) 6p e r f o r m e d o n t h e u n a l t e r e d , a i r - d r ie d s o i l c o n s ti t u e n ts a r e s h o w n

TABLE 2-- Ph ysi cal properties of soil constituents use d in sand-clay soil mixtures.

Soil C onstituent

AS TM Test Attapulgite GranularProperty/Characteristic Standard Cla y Bentonite Pow dery Bentonite San d

Source NA Floridin Co., Wy o-Ben, Inc., Quality Drilling, Colorado Lien Co.,Quincy, FL Billings, MT Greeley, CO LaPorte, CO

Trade name NA Microsorb-ES BigHorn CH 10 Quality Bentonite 40--140 Silca Sand

Liquid limit, LL (%) D 4318 305 405 413 --Plasticity index, PI (%) D 4318 209 367 378 NPSpecific gravity,Gs D 854 2.71 2.87 2.81 2.66Percent sand, 0.074--4.75 mm D 421 6.5 5.0 0 100Perc ent silt, 0.002-0.074 mm D 422 29.0 20.0 16.0 0Percent clay, < 2 ~m D 422 64.5 75.0 84.0 0Classificat ion (USCS) D 2487 CH CH CH SP

TABLE 3--C hem ical properties of soil constituents.

Soil Constituent

Attapulgite Granular PowderyProperty Clay Bentonite Bentonite Sand

Cation exchange capacity,CEC (meq/100 g) 18.1 63.9 72.3 0

Exchangeable m etals (meqlI00 g) :

Ca 5.9 18.6 26.6 .-.Mg 11.1 7.4 4.2 ...Na 0.1 29.8 36.3 -K 0.3 1.3 0.9 ---AI


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1 0 0

9 0

8 0

7 0C ~t -

~ 6 0f o

a . 5 0ol D

~ 4 0Q .

3 0

20

1 0

010'

L, Sa nd ~ l~ S i l t ~_1_~r - - ~ ~ i T ~ V l ~

HOWELL lET L ON CL Y SO IL MIXTURES

Clay ~

10 10 10 2 10 3 10 4 10 s

P a r t i c l e D i a m e t e r ( m m )FIG. l Particle size distributions fo r soil constituents used in the sand clay soil mixtures.

10

5

m e n p r e p a r a t i o n t o d e s t r o y t h e i n t a c t c l o d s o f t h e g r a n u l a rben ton i te .

Index Properties o f Soil Mixtures

F o u r s o i l m i x t u r e s w e r e u s e d i n t h i s s t u d y : s a n d m i x e d w i t hg r a n u l a r b e n t o n i t e ( S - G B ) , s a n d m i x e d w i t h p o w d e r y b e n t o n i t e( S - P B ) , s a n d m i x e d w i t h a t t a p u l g i t e c l a y ( S - A C ) , a n d s a n d m i x e dw i t h a t t a p u l g i t e c l a y a n d g r a n u l a r b e n t o n i t e ( S - A C - G B ) . T h e t o t a lc l a y s o i l c o n t e n t s ( i . e . , A C , G B , P B , o r A C + G B ) i n t h e s a n d -c l a y s o i l m i x t u r e s a r e. 1 0 , 15 , a n d 2 0 o f t h e d r y w e i g h t o f t h es o i l m i x t u r e . T h e c l a y s o i l c o n t e n t d i f f e r s f r o m t h e c l a y p a r t i c l econ te n t (i . e ., < 2 I~m) in tha t the c lay so i l con ten t i s the am oun to f a t t a p u l g i t e c l a y a n d / o r b e n t o n i t e a d d e d t o t h e s a n d - c l a y s o i lmix ture and , the re fore , inc ludes p a r t i c le s i zes > 2 I .tm as ind ica tedi n F i g . 1 . T h e u s e o f c l a y s o i l c o n t e n t i s i n a c c o r d a n c e w i t h p r a c t i c a la p p l i c a t io n s w h e r e t h e a m o u n t o f t h e p r o c e s s e d c l a y s o i l a d d e dt o t h e s a n d i s t h e p r i m a r y i n t e r e s t ( e .g . , a m o u n t o f b e n t o n i t e i n a

s a n d - b e n t o n i t e m i x t u r e ) . T h e c l a y s o i l c o n t e n t o f th e s a n d - c l a ys o i l m i x t u r e s c o n t a i n i n g b o t h b e n t o n i t e a n d a t t a p u l g i t e c l a y w a sc o m p o s e d o f e q u a l a m o u n t s o f t h e tw o p r o c e s s e d c l a y s o i l s ( i .e . ,5 0 e a c h b y d r y w e i g h t o f t h e c l a y s oi l a d m i x t u r e ) .

T h e m i n i m u m c l a y s o il c o n t e nt o f 1 0 w a s b as e d p r i m a r i l y o nt h e s t u d y b y K e n n e y e t a l . ( 1 9 9 2 ) , w h o f o u n d t h a t m a n y v o i ds p a c e s d i d n o t c o n t a i n b e n t o n i t e d u e t o i n a d e q u a t e d i s t r ib u t i o n f o rb e n t o n i t e c o n t e n t s < - - 7.4 . In s t e a d , K e n n e y e t a l . ( t 9 9 2 ) f o u n dt h a t a d e q u a t e d i s t r ib u t i o n o f t h e b e n t o n i t e i n t h e m i x t u r e o c c u r r e df o r b e n t o n i t e c o n t e n t s > - 9 . T h i s l o w e r l i m i t o n t h e b e n t o n i t ec o n t e n t a l s o i s c o n s i s t e n t w i t h t h e b e n t o n i t e c o n t e n t s b a s e d o nf i e l d m i x i n g c r i t e r i a r e p o r t e d b y L u n d g r e n ( 1 9 8 1 ) , G a r l a n g e r e ta l . ( 1 9 8 7 ) , a n d O ' S a d n i c k e t a l . (1 9 9 5 ) . C l a y s o i l c o n t e n t s g r e a t e rt h a n 2 0 w e r e c o n s i d e r e d u n r e a s o n a b l e f r o m a p r a c t i c a l v i e w p o i n td u e t o t h e l i k e l i h o o d o f e x c e s s i v e c o s t .

T h e m e a s u r e d a n d c a l c u l a t e d p r o p e r t ie s o f t h e so i l m i x t u r e s a r e

s u m m a r i z e d i n Ta b l e 4 . P l o t s o f p l a s t ic i t y i n d e x , P I , v e r s u s p e r c e n tc lay par t i c les ( < 2 I~m) a re sho wn in F ig . 2 fo r a l l mix tures .B a s e d o n S k e m p t o n 0 9 5 3 ) , t h e s l o p e s o f t h e s e p l o ts s h o u l d b e as t r a i g h t l i n e r e p r e s e n t i n g t h e a c t i v i ty, A ( = P I / < 2 i ~m ) , o f t h es o i l . A l s o , S k e m p t o n ( t 9 5 3 ) f o u n d t h a t t h e r e l a t i o n s h i p b e t w e e nP I a n d < 2 ~ m i n t e r c e p t e d t h e o r i g i n f o r n a t u r a l l y o c c u r r i n gs o i l s ( i . e . , a s o p p o s e d t o s o i l m i x t u r e s ) . H o w e v e r, S e e d e t a l .( 1 9 6 4 a ) t y p i c a l l y f o u n d t h a t t h e r e i s a n i n t e r c e p t o n t h e x - a x i s f o r

< 2 ~ m ( i .e . , th e l i n e d o e s n o t p a s s t h r o u g h t h e o r i g in ) f o rm i x t u r e s o f s a n d a n d p r o c e s s e d c l a y s o i l s . B a s e d o n t h e i r o b s e r v a -t i o n s , S e e d e t a l . ( 1 9 6 4 a ) m o d i f i e d S k e m p t o n ' s o r i g i n a l a c t i v i t ye q u a t i o n a s f o l l o w s :

A P IA = (1 )

A( < 2 I~m)

w h e r e A P I i s t h e c h a n g e i n p l a s t i c it y i n d e x , a n d A ( < 2 I~ m )i s th e c o r r e s p o n d i n g c h a n g e i n p e r c e n t o f c l a y p a r t ic l e s i z e s . R e s u l t sf rom Seed e t a l . (1964a) cons i s ten t ly ind ica ted an x - in te rcep t , Xo ,

of 9 . As ind ica ted in F ig . 2 , the so i l mix tures in th i s s tudy y ie ldx 0 v a l u e s r a n g i n g f r o m 5 .1 t o 5 . 7 . T h e a c t i v i ti e s o f t h e s a n d - c l a ys o i l m i x t u r e s b a s e d o n E q 1 a l s o a r e s h o w n i n F ig . 2 .

ompaction Water

A p r o c e s s e d ta p w a t e r ( P T W ) w a s u s e d f o r c o m p a c t io n . Ta pw a t e r w a s p a s s e d t h r o u g h t h r e e B a r n s t e a d c o l u m n s t o o b t a i nt h e p r o c e s s e d t a p w a t e r ( P T W ) . T h e m e a s u r e d p H a n d s p e c i f i c( e l e c t r i c a l ) c o n d u c t a n c e o f t h e P T W a t 2 5 C w e r e 7 . 1 a n d 3 2 . 8l~S/cm, respec t ive ly.

M e t h o d s

Specimen P reparationTw o m i x i n g p r o c e d u r e s w e r e u s e d t o e v a l u a t e t h e e f f e c t o f

m i x i n g o n c o m p a c t i o n . M i x i n g P r o c e d u r e 1 c o n s i s te d o f m i x i n g

Copyright by ASTM Int'l (all rights reserved); Wed Jun 17 14:35:14 EDT 2009Downloaded/printed byColorado State Univ pursuant to License Agreement. No further reproductions authorized.


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4 4 6 G E O T E C H N I C A L T E S T IN G J O U R N A L

TABLE 4 Physical properties of soil mixtures.

Attcrberg Limits b

Percent by Dry Weight of Clay SoilMixture in Sand-Clay Soil Mixture a Liquid Plasticity Specific

Limit, LL Index, PI Gravity,N o . A C G B P B To t a l (%) (%) G s

Particle Sizes c

Sand(0.074-4.75

mm), %

Silt(0.002-0.074

mm), %

Clay(


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HOWELL ET AL ON CLAY SOIL MIXTURES 447

com bined c lay so i l mix ture , and then adding tha t c lay so i l mix tureat arbi trary intervals to the wet sand.

Specimen Compaction

Specimens for each so i l mix ture were comp acted in accordancewi th s tandard com pact ion procedures (AS TM D 698) 8 . The opt i -mu m water conten t ,Wopt and the m axim um d ry unit weigh t , ~/dmax,for the resu lt ing comp act ion da ta were de te rmined by regress ingthe m easured da ta wi th a th i rd-order po lynomia l equa t ion of thefo l lowing form:

~ld = Aw3 + B w2 + Cw + D (2)

where ~a i s the dry un i t weight , kN/m3, w is the correspondingmold ing (com pact ion) water conten t , %, and A, B, C , and D areconstants result ing from the f i t ting process. Both sec ond -order andfour th-order po lynom ia l equa tions a l so w ere cons idered . How ever,a second -order po lynomia l equa t ion does no t a l low for the poss ib i l-i ty of an increase in Yd with a decre ase in w that can oc cur wh enthe m old ing w ater conten t i s s ign i fican tly dry of Wopt (Hausm ann1990), whereas a fourth-order polynomial equation f i ts four datapoin ts exac t ly and doe s no t p rovide s ign i f ican t ly g rea te r accuracyre la tive to a th i rd-order po lynom ia l equa t ion for m ore than fou rdata points , Thus, a third-order polyno mial equation is reasonable.

T h e l o c a l m a x i m u m a n d m i n i m u m o f a t h i rd - o rd e r p o l y n o m i a lf i t can be ascer ta ined by se t ting the der iva t ive of Eq 2 w i th respec tto w equal to zero, or

d~l_...aa= 3Aw2 + 2Bw+ C = 0 (3)dw

and so lv ing the resu l t ing q uadra t ic equa t ion for the tw o roots o fw, or

B - i 2 A C

w = -3 A - 6A (4)

The value of w correspo nding to ~/araax is Wop , an d ~/amax isdeterm ined b y su bst i tut ing Wopt into Eq 2, or:

~amax = aw3p t + Bw~opt + Cwo pt + D (5)

Since mo s t sof tware p lo t t ing pa ckages provide for th i rd-orderpolynomial f i t t ing, and the roots of the f i t ted curve (Eq 4) can bedeterm ined using a hand-held calculator, the above analysis forWop and ~/arnax is straightfo rwa rd, y et provid es a con sistent an dra tiona l bas i s for eva lua t ing the d i ffe rences amon g d i ffe ren t com-pac t ion curves . A sum mary o f the resu lt ing f i t ting param eter va luesand corre spo nd ing Wop and Yamaxvalues for the com pact ion tes t sperformed in this s tudy is provided in Table 5. Presentat ion of themeasured d a ta and d iscussion of the resu l ts fo l lows .

R e s u l t s a n d i s c u s s io n

Effect of Clay Soil Type

The s tandard compact ioncurves (ASTM D 698) for Test Nos .1-12 (Table 5) per formed to d i s t inguish the type o f p rocessed c laysoil in the sand-clay soi l mixtures onWoptand ~dmax are shownin F ig . 3 . The shape of the th i rd-order po lynom ia l f i t to the m ea-sured da ta for powdery bentoni te (F ig . 3e) may be due to the

8Test Metho d for L aboratory Com paction Characteristics of Soil UsingStandard Effort (12,400 ft-lbf/ft3 (600 kN-m/m3)).

a rch ing e ffec t tha t resu lt s f rom comp act ion a t mold ing water con-tents that are s ignif icantly dry of Wop as described by Hausmann(1990), o r s imply m ay b e the resu l t o f sca t te r in the da ta on thedry side of W~pt.

Th e trends in Wop and ~/amax with clay soi l content for thecompaction curves in Fig. 3 are shown in Fig. 4. As expected,Wop increased a nd 'Ydmax decrea sed as the a mo unt o f at tapulgitec lay in the mix ture increased f rom 10 to 20%. These t rends a reexpe cted since cla y soi ls typ ical ly have lowe r Ydmax values andhigh er Woptvalues than sa nds; thus, an increase in clay soi l contentis expe cted to dec rease ~/dmax and to increaseWop . Howev er, thesam e trends in W opt and ~/amax are n ot evide nt fo r the m ixturescontaining bentonite .

For exam ple, Ydmax or the sand-gran ular bentonite (S-GB) mix-tures is relat ively insensi t ive to the clay soi l content , whereas~/dmax for the san d-po wd ery ben tonite (S-PB ) m ixtures increasesas the powd ery bentoni te conten t increases f rom 10 to 20%. Therelat ive insen si t ivi ty o f the ~/dmax values tO the clay soi l con tentfor the S-Giq mixtures m ay b e at tr ibuted, in part , to the similari ty

betwe en the part icle-size distr ibution for the sand and the pa rt icle-s ize d i s tr ibu tion for the granular ben toni te based on the m echanica l(sieve) analysis of the air-dried soi l as shown in Fig. 1.

Th e trend in Ydmaxversus clay soi l content for the S-PB m ixturesis somewhat consistent with Kenney et al . (1992), who reportedan increase in ~dmax until abou t 16% be ntonite content fol lowedby a de crease in ~/amax with increasing b entonite co ntent . In thiscase , the smal le r pan ic les o f the powd ery bentoni te f il l the vo idspaces be tween the la rger san d par tic les . The d i ffe rence be tweenthe resu lt s repor ted by K enney e t a l . (1992) and those repor tedfor the powdery bentoni te m ix tures in th i s s tudy may be due , inpar t , to the d i ffe rences be tween the sand andbentonites used inboth s tud ies . F or exam ple , the sand used b y Kenn ey e t aL (1992)conta ined 2% f ines (% < 0 .075 ram) , whereas the sand used inthis s tudy contained no f ines (Table 2) .

Sin ce the Yarnaxvalues for the granular and pow dery bentoni tesare bo th lower than the ~amax va lues repor ted in Table 5 and shownin Figs. 3 and 4 for the S-G B an d S-PB mixtures, the ~/amaxvaluesfor the sand-bentoni te mix tures should decrease eventua l ly as thebentoni te conten t increases towards 100%. In the case of the S-PB mixtures , a peak 3 'amax va lue a t a c lay so i l conten t pas t 20%also would be cons is ten t wi th the t rends repor ted by Kenney e tal . (1992). T hus, addit ional com paction curves we re generated forbenton ite contents of 30, 40, 60, and 80 % to invest igate thisexpe cted trend. Th e result ing ~amax values for these com pactioncurves are plot ted together with the previously reported ~/amaxvalues for bentonite contents o f 10, 15, 20, and 100% as a function

of bentonite content in Fig. 5.Th e data in Fig. 5 for both the S-G B and S-PB mixtu res indicate

the expe cted trend. The da ta in Fig. 5 also indicate that the differ-ence s in ~/amax values, or A'Yamax, for b entonite contents rangingfrom 10 to 20% are small relat ive to the overal l A~/dma fo r benton-i te conten ts ranging f rom 10 to 100%. For example , the maxim umA~/ama va lues for benton ite contents between 10 and 20% areonly 2 .1 and 9 .2% of the max imu mA Ydma values for bentoniteconten ts be tween l0 and 100% for the S-GB and S-PB mix-tures, respectively.

As shown in Fig. 4, there is no signif icant peak in the trend of/dmax versus benton ite conten t for the sand-granular b entonite (S-

GB ) mixtures, whereas the peak Ydmaxvalue occurs for the benton-i te conten t o f 20% for the sand -powdery bentoni te (S-PB) m ix tures .However, the second-order po lynomia l f i t to the da ta for the S-PB mixtures is essential ly a s traight l ine ( i .e . , third term in equa tion



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8 G E O T E C H N I C A L T E S T I N G J O U R N A L

TA B L E 5---Compaction properties base d on third order polyno mial fits to measure d compaction data fo r sand-clay soil mixtures.

C o m p a c t i o nProper t iesa

Dry W eight Percent of Clay Values for Cons tants in F i t ted Polyno mia l Expres s ion and ~/dmaxS o i l i n M i x t u r ea C u r i n g C o r r e s p o n d i n g C o e ff i c i e n t o f D e t e r m i n a t i o nc

Te s t M i x i n g P e r i o d, w ~ t ,

N o . A C G B P B To t a l P r o c e d u r eb days A B C D r 2 N kN/m 3 ib / f t3

1 100 . . . . . . 100 1 I 2 .70 10 6 -0 .00 20 7 0 .217 2 .61 1 .000 5 59 .3 8 .75 55 .72 1 0 . . . . . . 1 0 1 1 0 . 0 0 0 3 9 5 - 0 . 0 3 4 4 0 . 7 6 5 11 . 1 0 . 9 6 6 1 0 1 5 .0 1 6 . 20 1 03 .13 15 . . . . . . 15 1 1 0 .000379 -0 .0 32 7 0 .753 10 .4 0 .987 11 15 .9 15 .66 99 .74 20 . . . . . . 20 1 1 0 .000346 -0 .0 32 4 0 .787 9 .78 0 .955 11 16 .5 15 .51 98 .75 - - . 100 . . . 100 1 1 0 .000262 -0 .02 83 0 .974 1 .93 0 .903 6 28 .4 12 .76 81 .26 - -- 10 . . . 10 1 1 -0 . 000 496 0 .0186 -0 .2 00 16 .5 0 .988 10 17 .0 16 .06 102.27 15 . . . 15 1 1 -0 . 000 143 0 .000668 0 .0754 15 .2 0 .961 8 14 .9 16 .03 102.08 . . 2 0 . . . 20 1 1 0.000261 -0 .0 20 1 0.407 13.6 0.997 6 13.9 16:10 102.59 . . . . . . 1 0 0 1 0 0 1 1 - 0 . 0 0 0 9 3 7 0 . 0 9 01 - 2 . 8 4 4 1 . 6 0 . 9 8 4 5 3 5 . 9 1 2. 25 7 8 . 0

10 . . . . . . 10 10 1 1 -0 . 00 115 0 .0416 -0 .4 47 17 .8 0 .999 6 16 .2 16 .61 105.711 . . . . . . 15 15 1 1 -0 . 000 524 0 .00839 0 .0961 15 .3 0 .999 5 14 .8 16 .84 107.212 . . . . . . 20 20 1 1 -0 . 000 188 -0 .0 10 4 0 .419 13 .7 0 .989 7 14 .5 17 .05 108.513 - - 10 - . . 10 1 7 -0 . 000 506 0 .0189 -0 .1 98 16 .4 0 .999 6 17 .3 16 .01 101.014 -- . 15 . . . 15 1 7 0.0001 43 -0 .0 14 5 0.336 13.8 0.992 6 14.8 16.09 102.415 . . . 20 20 1 7 -0 . 000 177 5 .96 10 -6 0 .1200 14 .9 0 .996 6 15 .0 16 .11 102.516 . . . . . . 10 10 1 7 -0 . 000 868 0 .0297 -0 .2 87 17 .1 0 .898 7 15 .9 16 .57 105.517 . . . . . . 15 15 1 7 -0 .00 14 2 0 .0507 -0 .5 53 18 .6 1 .000 5 15 .4 16 .89 107.51 8 . . . . . . 2 0 2 0 1 7 - 0 . 0 0 0 1 4 4 - 0 . 0 1 3 1 0 . 4 6 8 1 3 .4 0 . 9 9 4 6 1 4 .4 1 6 .9 7 1 0 8 .019 - - 10 - - . 10 2 7 -0 . 00 115 0 .0483 -0 .6 26 18 .6 0 .988 7 17 .8 16 .27 103.620 - - 15 - - - 15 2 7 -0 . 00 012 9 -0 . 00 31 5 0 .186 14 .6 0 .997 5 15 .3 16 .28 103.62 1 - 2 0 - -- 2 0 2 7 - 0 . 0 0 0 6 7 3 0 . 0 22 1 - 0 . 1 6 9 1 6 . 1 0 . 9 6 8 5 1 6. 9 t 6 . 3 0 1 03 .72 2 . . . . . . 1 0 1 0 2 7 - 0 . 0 0 2 6 4 0 . 1 0 8 - 1 . 4 1 2 2 . 4 0 . 9 9 9 5 1 6. 5 1 6 .7 5 1 0 6 .62 3 . . . . . . 1 5 1 5 2 7 - 0 . 0 0 1 8 4 0 . 0 7 0 8 - 0 . 8 6 7 2 0 . 2 0 . 9 9 5 5 1 5. 5 1 6. 91 1 0 7 .624 . . . . . . 20 20 2 7 -0 .0 048 1 0 .144 - 1 .25 19 .5 1 .000 4 13 .7 17 .13 109.025 5 5 - -- 10 Batch 1 -0 . 00 034 9 0 .0122 -0 .1 08 16 .1 0 .999 5 17 .3 16 .05 102.226 7 .5 7 .5 - -- 15 Batch 1 3 .86 10 -5 -0 .0 11 4 0 .334 13 .3 0 .999 6 15 .9 15 .92 101.327 10 10 - -- 20 Batch 1 0 .00186 -0 .1 06 1 .93 4 .32 0 .976 5 15 .5 15 .86 100.928 5 5 - -- 10 Indiv idual 1 -0 .0 077 1 0 .388 -6 .4 4 51 .4 0 .717 6 18 .6 16 .32 103.929 7 .5 7 .5 - -- 15 Indiv idual 1 -0 .0 02 46 0 .115 -1 .7 2 24 .2 0 .971 6 18 .6 16 .07 102.330 l0 10 - - . 20 Indiv idual 1 -0 .0 004 87 0 .0113 0 .0303 14 .6 0 .900 7 16 .7 15 .97 101.6

~,prAC = attapulg ite clay; GB = granu lar bentonite ; PB = pow dery be ntonite.ocedure 1 = a dd water to sand before mixing wi th c lay so i l; Procedure 2 = mix sa nd and c lay so i l before adding water ; Batch = add water

sand before mixing w i th c lay so il mixtures taken f rom a la rge ba tch of mixed c lay so i l ; Indiv idual = add water to sand before m ixing wi th c lay smixtures based on indiv idual mixtures of c lay so i l .

CA, B, C, and D arecons tants in the th i rd-ord er polynom ia l express ion ~ td =Aw3 Bw2 Cw D,where 3 'a i s dry uni t weight (kN/m3) , and wis molding water con tent (%); r 2 = coeff ic ien t of de terminat ion ; N = No. o f compact ion tes t s.

dwop = opt im um w ater content and ~/dmax = ma xim um dry uni t weight based on AST M D 698.

i s n e g l i g i b l e ) , i n d i c a t i n g t h a t t h e ' ~ /d ma x v a l u e s f o r b e n t o n i t e c o n -t e n t s o f 1 0 , 1 5 , a n d 2 0 % a r e i n t e r p r e t e d e s s e n t i a l l y a s s c a t t e r int h e d a t a i n t e r m s o f t h e r e g r e s s i o n a n a l y s i s ( i .e . , n o t r e n d i s i n d i c a t e db e t w e e n 1 0 a n d 2 0 % c l a y s o i l c o n t e n t s ) . T h u s , a c c u r a t e t r e n d s i n~ /d m ax v a l u e s v e r s u s b e n t o n i t e c o n t e n t s a s s o c i a t e d w i t h r e l a t i v e l yl o w b e n t o n i t e c o n t e n t s t y p i c a l o f p r a c t i c e ( i .e . , < - -2 0 % ) m a y b e

d i f f i c u l t t o o b t a i n d u e t o t h e r e l a t iv e l y s m a l l d i f f e r e n c e s i n t h e s eYdmax va lu es .

A s s h o w n i n F i g . 4 , w o pt f o r b o t h t y p e s o f s a n d - b e n t o n i t e m i x -t u r e s d e c r e a s e s w i t h i n c r e a s i n g b e n t o n i t e c o n t e n t r e g a r d l e s s o f t h et y p e o f b e n t o n i t e . T h i s t r e n d i s n o t c o n s i s t e n t w i t h t h e s a n d -a t t a p u lg i t e c l a y ( S - A C ) m i x t u r e s, n o r w i t h K e n n e y e t a l . ( 1 9 92 ) ,w h o f o u n d a n i n c r e a s e i n Wo p t w i t h i n c r e a s i n g b e n t o n i t e c o n t e n t .A l s o , t h e t r e n d o f d e c r e a s i n g Wop t w i t h i n c r e a s i n g b e n t o n i t e c o n t e n ti s n o t d u e t o th e t w o d i f f e r e n t t y p e s o f b e n t o n i t e c o n s i d e r e d i nt h i s s t u d y s i n c e t h e s a m e t r e n d i s o b s e r v e d f o r b o t h t y p e s o f s a n d -b e n t o n i t e m i x t u r e s .

T h e d i f f e r e n c e i n t h e t r e n d o f Wo pt v e r s u s b e n t o n i t e c o n t e n t f o rt h e s a n d - b e n t o n i t e m i x t u r e s r e la t i v e t o th e S - A C m i x t u r e s m a y b ed u e , i n p a r t, t o th e g r e a t e r s o r p t i v i t y a n d l o w e r s w e l l i n g p o t e n t i a lo f t h e a t t a p u l g i t e c l a y r e l a t i v e t o th e b e n t o n i t e , a s i n d i c a t e d i n Ta b l e1 . A s a r e s u l t , a t t a p u l g i t e c l a y a b s o r b s w a t e r w i t h o u t s i g n i f i c a n t

s w e l l i n g . T h i s h i g h e r w a t e r h o l d i n g c a p a c i t y f o r a t t a p u l g it e c l a yi s r e f l e c t e d b y a Wop f o r a t t a p u l g i t e c l a y o f 5 9 . 3 % , w h e r e a s t h eWop t v a l u e s f o r t h e g r a n u l a r a n d p o w d e r y b e n t o n i t e s a r e o n l y 2 8 . 4a n d 3 5 . 9 % , r e s p e c t i v e l y ( Ta b l e 5 ).

T h e t r e n d o f d e c r e a s i n g Wop t v e r s u s i n c r e a s i n g b e n t o n i t e c o n t e n ta l s o m a y b e r e l a t e d t o t h e c o r r e l a t i o n b e t w e e n Wop a n d P L p r e -

v i o u s l y n o t e d b y L e r o n e i l e t a l. ( 1 9 9 2 ) , a n d t h e c o r r e l a t i o n b e t w e e nt h e P L a n d c l a y p a r t i c l e c o n t e n t ( % < 2 p , m ) f o r s a n d - c l a y s o i lm i x t u r e s p r e v i o u s l y n o t e d b y S e e d e t a l. ( 1 9 6 4 a , b ) . I n te r m s o fa c o r r e l a t i o n b e t w e e n Wop a n d P L , L e r o u e i l e t a l . ( 1 9 9 2 ) i n d i c a t e dthat Wop ~ P L f o r n a t u r a l c l a y s o i l s (i . e. , a s o p p o s e d t o s a n d -b e n t o n i t e m i x t u r e s ) . A s s h o w n b y t h e d a t a p l o t te d i n F ig . 6 a , t h ec o r r e l a t i o n b e t w e e nWop a n d P L f o r s e v e ra l c o m p a c t e d c l a y s o i l si s c l o s e t o l : l , b u t t h e r e i s s i g n i f i c a n t s c a t t e r i n t h e d a t a ( r 2 =0 , 7 3 2 ) . A l s o , a s a l l u d e d t o b y L e r o u e i l e t a l . ( 1 9 9 2 ) , L a m b e ( 1 9 5 9 )h a d c r i t i c i z e d t h e a s s u m p t i o n t h a tWop ~ P L o n t h e b a s i s t h a t t h ec o r r e l a t i o n b e t w e e n Wo p a n d P L i s n o t u n i t y f o r p u r e c l a y m i n e r a l s .T h i s c r i t i c i s m i s s u p p o r t e d b y t h e d a t a i n F i g . 6 b t h a t i n d i c a t eWop

0 . 5 P L f o r p u r e c l a y m i n e r a l s, a l t h o u g h t h e r e i s l e s s s c a t te r i nt h e d a t a i n F i g . 6 b ( r2 = 0 . 9 5 1 ) r e l a t i v e t o F i g . 6 a . T h u s , t h e r ea p p e a r s t o b e a c o r r e l a t i o n b e t w e e nWop a n d P L , b u t t h i s c o r r e la t i o ni s n o t c o n s i s t e n t b e t w e e n n a t u r a l c la y s o i ls a n d p u r e c l a y m i n e r a ls ,



7/16

H O W E L L E T A L . O N C L A Y S O I L M I X TU R E S4 4 9

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" ~ ' , ' + + ' , - + - ; - + ' , . . F . ~ ~ , - + - , - . + - + - - i . + + . +~ _ . ^ ~ : i . . , + | . + . ' ~ + ~ ~ . ~ : ~ . + ~ | . ~ . |

l = 0 0 ~ . ' * ' ) '* ' ~ ' ' . ~ . ~ . : ~ ' ~ ~ . ~ . + k - ~ . ~ . . ~ - ~ . - ~ . ~ - - ) + - ~ . - ~ - ~ + + - H - + + . . - + - " . : .' + - : . * *" . : . . : . : - . ; + = :

~ + . + -+ - + ' + - $ . + . + 4 - - + - & ~ - 4 + ' . ; a b - - , . . . . . . ,o ' + .~ " + . , . . . .

u - ~ . . , . + . , . + . , . ~ : i : # . , + . , . ~ . += - I- + .= . .* * .. ~ * * . + . ; + . ~ , ~ ~ p . + ~ . i . . I r + ~ . ; + . = . . t k + ; - - ' - + " . i 4 11 ++ + ~ " .L ~ ..+ ~ +.+ ~ ..; .: ..: " ;+

o ~ : - - t - . % + + - + ~ ~ + , - ~ . +: ,.~ +- +4 ~-; ~ -+$ , ,: ~ + : : : + : : ~ : ~ : : . ; . ~ + + - * *o . + . ; . . . . p . . + L . ~" ~ + - P < . k+= 8 2 : ~ + . , . ~ . + + : + ~ + : + ~ + . + . ,

;= : + :~ :+ : " '~ ."t: ' :

t - - = - e - :+ - . : .* t . . t . - ~ - - 1 . + - . . : . . . L" 7 ~ : _ I - " l ' f ' * ) ' * l ' 4 " ' | * ' t * 4 + l ' l " ) ' < " | ' ' l + ~ i ' ; ' "' . = . 4 - ' 4 * . : . . ' . | . . % 4 . * * . . ' . ; + . . . . . .

, . v ' ~ ' ' I ' ' ' ' I ' ' ' ' I ' ' ' ' I ' ' ' ' I ' ' ' '

3 0 4 0 5 0 6 0 7 0 8 0 9 0M o l d i n g Wa t e r C o n t e n t , w ( % )

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.,t : + ~ i .,'~tl~:~..t. :+:b;+ l . . . . +i 2 . 2 ~ + .: : ~ " .~ + .=-++.+,~. . . . . + 3

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. :. .; . . . . . . . . . . + . . : + + : - . , L + : . + . . ~~ i i ~ + . , . + . + + , . . . . . . i . , . + . < . . ' ~

4 8 . 4 5 1 0 1 5 2 0 2 5 3 0 3 5 4 0

M o l d i n g Wa t e r C o n t e n t , w ( % )

( c) G r a n u l a r B e n t o n i t e ( G B )l " : l " J + l , , , , l , ,, , l , , , , I , , , , I , ,, ,

~ e ~ l l I t a I I I I I I I I i T I I i i + ~ i i I r

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v 1 - - p . l - [ . . t l , , + , , ~ r + . . ~ . .. ~ ( ~ p + t p ; . + . + + .. + .~ . 4 + + + 1 - - - - - + - - - p ~ v - - + - . c , . . p + . - - < + - ~ - . + . + . . + + + , , - . ~ , . ; . +

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, , . : - - r - r T- : . T- - T T = 7} 1 2 . . -; - +.-+.+++-+-+-.

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2 0 2 5 3 0 3 5 4 0 4 5M o l d i n g Wa t e r C o n t e n t , w ( % )

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. 7 9 . 0 ~ ~ , -~ I ~ " 1 5 %G B | - . ' . ' .e .+. j . t .+~.i . j . t .p++0 4 4 . ~ o / ~ _ o +z+H-+++:+-;++++.~-I- 1 4 + a r - ,~ u /o , .+ u t.++-;++.+'~+~,.++.~-~+-~-~L

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5 1 0 1 5 2 0 2 5 3 0 3 5 4 0


( e ) P o w d e r y B e n t o n i t e ( P B )

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+ . . . . . . . + . . . . . . . . . ~t " ' , .~ ~ . " ' '" : : , : : + 1 " ~ ' ' : ' : ' " T " . ' . " : " + = ' [ "~ , T :I . .. .. ..-~,-,..,-+,.+,+-~'+4 :~+......... ...~ . . i . i i . i . | . ' t i . + . . i . . i . . Z . i + q . ; . . ; . $ . $ . $ . 4 . 3 , $ . ; . 4 4 . + i

+ : 1 2 1 - ~:..;..;..,.++ ..t.+.z+ .L~ . +.+..+..+ +.. , , , + + , . . . . . ++" C ; I . + . : .; . - ; + . + . .= . . : .: + . . : + + + . ~ . : + . L + & . . L ~ . ~ . . ~ + ~ . - : U . : : . : 3 _

:o l : : h : : + : : i : ~ : , ' : ~ : + . . - +.::-.~~ , 1 2 . o . H + + - i - ~ . . . - : ' ~ - - ~ - + : : . " : : : ' : : : ' :

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H - - * - - < - ' - - i - - i - - + - - + . . ' - - + - ; + . + ~ + ; . . ' - + + - - ; . + . + 4 4 + + + -

( t) S a n d - P o w d e r y B e n t o n it e ( S - P B )7 9 . 0 . . . . 1 7 . 5 t . . . . I . . . . I , . , , . . . . l . . . . l . . . . I . . . . l 4 t 4 =

L~.~ +, .L. , , . / .LL ,. I , , , II P : 1 " ' " ~ ' : ' " " " . '+ '

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8 . 4 ~ 1 7 . 0 - . . . . . ~ ~ : , . ~ = ~ ~ - 1 0 8 . 3.+.;.+..~+~.; +.~.'+, - - A - - 2 0 ~ P B

o ) 1 6 . 5 - - { . + . ~ , " ~ - - . j - l - { - ~ - ' 4 - i o W 4 - ~ - i { - { ~ l . ~ - ~ 1 - 1 0 5 . 1

: . 7 7 . 1 -+-= : .-+-i-+-++.:-+-+-}-i++ ~+:'+:'-i-+-i;+-~-+.+. + H+.++ +.H+++.;.+.+.+++"~ "~ .+.~-++. :+-+-++>+- .,-+, H'+-++++.-H.i.++++-H+++" "~o , 1 ,

7 6 . 4 ~ O ~a.'-.'..:.u-.'..:.~..=.=..ii~i[i~ { [ ~ i ~ : " u a " L " ~ ' a ' " + " ' : : : ~ , ~ r ~. L : . . Z Z + . L . + - : . .. : .. + . L Z Z + .+.'.L~+..:.i.i++++,+.+.~.+.;.:. ; . + ~ + + L ; . i . i .+ . ~ 4 . i . L i . + . ~ 4 . : " . ~ . . ~ 4 . i . L ~ . ~ 4 . i . i i . ~ . . L ;

. , , , . . . . . . , - , ; , , , , , , , , , , , o, , + , I , , + ~ I , , , ~ I ~ I , , , , I + , , , I , + , , I + u . + ,

2 0 2 5 3 0 3 5 4 0 4 5 5 1 0 1 5 2 0 2 5 3 0 3 5 4 0M o l d in g W a t e r C o n t e n t , w ( % ) M o l d i n g W a t e r C o n t e n t , w( % )

FIG. 3--Stan dard compaction curves ASTM D 698) fo r processed clay soils and sand-clay soil mixtures fo r a one-day curing period and MixProcedure t



8/16

4 5 0 G E O T E C H N I C A L T E S T IN G J O U R N A L

S a n d - A t t a p u l g i t e C l a y ( S - A C )_ - ~ - S a n d - G r a n u l a r B e n t o n i t e ( S - G B }

- S a n d - P o w d e r y B e n t o n i t e ( S - P B )

.=

C

C

E

Et n

5 1 0 1 5 2 0 2 5

Clay Soil Content ( )

. ' -" 1 7 . 5 ' ' ' = I , , i , 1 1 1 . 4I i i E , w i i ~ I ~ I T ~ I i ' " ' ~ . L ,

E P-~.-~-+-~~ ~ . ~ - - +- -- ~- ~- - : i ~ : . : ,

I _ . . . L J - _ ~ E i " i i i , | ~ " " i _

Je , 1 7 . 0 . 1 - - I - + - - + . . . . . . . . . . . . . . . . . . - ~- -'- -~ -~ .'- ,- -4 -: '~ 4 ~.- 4- -~ -- -~ - - - 1 0 8 . 2

i ~ i i , ," i I i i , , i i i iI - . - - _ L . . . . . . . . . . ~ - l~ . i' ~ . . . . . - 4 - . . . . . . . ' -

t"-l~-t--~'-- ""~ i . - - ' ~ ~..t---4----i---~. .-,,~.~. 4---~-----4----I-.--i-.--.~----i ......~ : 1 6 . 5 . . . . . . . . . . . . 1 0 5 . 0 - -, , f - - i . . . . + - -- .~ - - ~ --~ - - - - t - - , - -~ - -- ~ . . . . . - - l -@ - . . . . . . . . . . ;

L.....L_ i ~ I i ~ i i I i i i i i i i l: : : : ) t " t - - t ' , ' - ~ - - - ~ : - - t - . ~ ~ .- .~ - ., - - - - +- ~-~ ... .... .... ... t - -1 -"" r ....

I l i i t i i " k i i i t t i I i i i t ~ 1

E ~ I r P - 1 ~ ' / ' ' ' ' 1 - - f - ' ' I ; i ~ i - - - ~ - . , t - - - - ~ - . , t - . - - - l - - - i~ . d .. i t i t t i: . - t - . 4 - - - - - . - = , - - - - i - ii - . . . E ~ " - " - - t - f - i - - i, , --4,--,'---,.'~-+-:=--4-~--'---:'---~"---------""--~-,i. ~ i ~ ~ ~ , ~ ~..... - x

' ~ - C ' ' ~ - - ~ . . . . ~ - - - - t . . - - ~ . * ~ + . - - . - . . ~ . i . ~ . . ~ . . . . . . . . . . i . .. . .. . i. . .. . .+ . t .. - .- . ( l i

i i l I ,~ i ; ~ i i ; i l ;

I 1 5 . 5 # ~ ~ I ~ ~ i 9 8 . 7

5 1 0 1 5 2 0 2 5

C l a y S o i l C o n t e n t( % )

F I G . 4---Influence of clay soil content on a ) optimum water content and b ) maximum dry unit weight fo r a one-day curing perio d and MixingP r o c e d u r e 1

and no such cor re la t ion be tween Woptand P L has been es tab l i shedfor sand-c lay so i l mix tures .

In t e rms o f a cor re la t ion be tween P L and c lay par t i c le con ten t ,Seed e t a l. (1964b) eva lua ted m easured p las t i c l imi t s o f va r iousmix tures o f a washe d sand and severa l p rocessed c lay so i l s (ben ton-i te , kaol ini te /bentoni te , and i l l i te /bentoni te) a t several c lay part ic lecon ten t s (% < 2 l~m) . Seed e t al . (1964b) fou nd tha t the PL ofthe mix tures in i t i a l ly decreased wi th inc reas ing c lay par t i c le con-t e nt s t o a m i n i m u m P L o f a p p r o x i m a t e ly 2 0 a t c l a y p a r ti c le c o n t e n t sr a n g i n g f r o m ~ 3 0 t o ~ 4 0 % a f t er w h i c h th e P L o f th e m i x t u re s

inc reased and u l t imate ly approa ched the l imi t ing P L va lue assoc i -a ted wi th the p rocessed c lay so i l . The in i t i a l dec l ine in PL wi thincreas ing c lay par t i c le con ten t was exp la ined by Seed e t a t .

( 1 9 6 4 b ) a s d u e t o t h e d o m i n a n c e o f t h e n o n c l a y f r a c t i o n o ft h emixture a t r e la t ive ly low c lay par t i c le con ten t s ( i . e . , -


9/16

HOWELL ET AL. ON CLAY SOIL MIXTURES 451

1 9 . 0

1 8 . 0 .

P. '= 17.0-

z~ 16.0-

1 5 . 0 -

g 1 4 . 0 -E

E 1 3 . 0 -x

1 2 . 0

0

, i : : : j . . . . t , , , t , , , 1 2 0 9; ; " i I . . . .I + S ~ l n d - G r a n u l a r B e n t o n i t e ( S - G B ) ]

- C ~ -Sand-Powdery Bentonite ( S - P B ) ' 1 1 4 . 6

. ., ~ 0 ~ Y ,~ (kN/m=) = 17 .5 - 0 . 05 1 5C 10 8 .2

~ ( r= = 0 9 7 2 ) -101.895.5

,. ~ 89 .1Y,m, (kN/m=) = 16 .2 - 0 .0 07 77 C - .

-0 .00 02 58 C ' (d=0 .991) -~ . 82 .7

: : : | : : : . . . . . . . . I ' ' i t I i I 7 6 . 41 I2 0 4 0 6 0 8 0 10 0

C l a y S o i l C o n t e n t , C , ( )

6o .

i

e-

c-

a

E

Ex

E

FIG. 5-- Inf luence of bentoni te content on maximum dry uni t weight for a one-day cur ing per iod a nd Mixing Procedure 1 .

A 50

. 4 0 -

oCo 3 0 -(3_ =

2 0 -

EE 1 0

. . , I . , , I . . . . I . , , I ,

v/ap = 0 .94 0P L (r2 = 0 .732)0

//

/ 4

a)/

0 : : : : : : : : : : : : : : : : : : : : : : : :

0 1 0 2 0 3 0 4 0 5 0Plas t ic Limit , P L (%)

Daniel (1984)A Boyn tonand Daniel (1985J Day and Daniel (1985) Mundel land B ailey (1985)O S tewar tand No lan (1987)A Danie land Benson (1990)[ ] E l sburyet al. (1990)


10/16

4 5 2 G E O T E C H N I C A L T E S TI NG J O U R N A L

4 O

~ . g 3 5 -0 .....T. j ca . ~ 3 0 -

-~ e 2 5.__.

0

1 00

: : i : : ; ~ : : : ~ : ; , t :

- - 1 ~ - P L ] ( a ) ~

P L = 3 0 . 9 - 0 . 5 5 ,C = + o . o o e 2 , c d : = 0 9 r 2 ) / i

q o E o o, . w, p , = 1 7 . 5- 0 .1 6 6C = = + 0 . 0 0 2 6 6 0 ~ 2 ( r= = 0 . 9 2 0 )

. . . 2 , , , , I ; : : : . : : I4 0 6 0 8 0 1 0 0Cla y Soil Content, C ( )

4 0

,. ~ g 3 5 .O . . r

3 0 .

~ 2 5 -

E~= 15-O

1 00

: : ~ = : : : : : I , I I I ,

PL ] (b)

-E::} - Wop/ /

0 . 3 ~ c = + 0 . 0 04 2 9 c ~ ~ = o . 9 7 2 ) /L 2 8 . 0 -/ /

E l

w = 1 9 . 2 - 0 . 3 2 1 C + 0 . 0 0 4 7 3 C 2 ( i, 2 = 0 .9 6 1 ): : , I ~ , , , , i ' ~ I =, , , : ; ' , , ,

2 0 4 '0 6 0 8 0

Clay Soil Content , C c~ ( )

O0

FIG. 7--Influence of bentonite content on plastic limit and optimumwater content of (a) sand-granular bentonite S-GB) mixtures, and (b)sand-powdery bentonite S-PB) mixtures or a one-day curing period andMixing Procedure 1.

descr ibed . The t rends in PL versus ben ton i te con ten t fo r bo th thesand-granu la r ben ton i te (S-GB) mix tures and the sand-powdery ben-ton i te (S-PB) mix tures fo l low c lose ly the same t rends desc r ibed bySeed e t a l . (1964a , b ) . Also , based on second-order po lynomia l f i t sto the da ta in F ig . 7 , a min imum PL of 18 .5 occurs a t a ben ton i tecon ten t o f 44 .7%, cor responding to a c lay par t i c le con ten t o f 33 .5%for the S-GB mix tures (F ig . 7a ) , whereas a min imu m PL of 20 .3

occurs a t a ben ton i te con ten t o f 42 .3%, cor responding to a c lay par t i c lecon ten t o f 35 .5% for the S-PB mix tures (F ig . 7b) . These min imumPL v a lues and co r responding c lay par t i c le con ten t s agree ve ry c lose lywi th the va lues p rev ious ly repor ted by Seed e t a l . (1964b) fo r s imi la rsand-c lay so i l m ix tures .

The Wop da ta in F ig . 7 a l so exh ib i t a s l igh t in i t i a l dec rease wi thi n c r e a s i n g b e n t o n i t e c o n t e n t f o l l o w e d b y a n i n c r e a s e i nop ast h e b e n t o n i t e c o n t e n t a p p r o a c h e s 1 0 0 % . B a s e d o n t h e s e c o n d - o r d e rp o l y n o m i a l f i t s t o t h e d a t a s h o w n i n F i g . 7 , a m i n i m u m Wo p o f1 5 . 1 % o c c u r s a t a b e n t o n i t e c o n t e n t o f 2 1 . 8 % , c o r r e s p o n d i n g t oa c l a y p a r t i c l e c o n t e n t o f 1 6 . 4 % f o r t h e S - G B m i x t u r e s ( F i g . 7 a ) ,w h e r e a s a m i n i m u m op o f 1 3 . 8 % o c c u r s a t a b e n t o n i t e c o n t e n to f 3 3 . 9 % , c o r r e s p o n d i n g t o a c l a y p a r t i cl e c o n t e n t o f 2 8 . 5 % f o rt h e S - P B m i x t u r e s ( F i g . 7 b ) . H o w e v e r, t h e g e n e r a l t re n d o f d e c r e a s -i n g Wo pt w i t h i n c r e a s i n g b e n t o n i t e c o n t e n t s f r o m l 0 t o 2 0 % i s s os l igh t r e la t ive to the overa l l t r end in theop d a t a t h a t a n y q u a n t i t a -

t i v e c o n c l u s i o n r e g a r d i n g a c o r r e l a t i o n b e t w e e n P L a n d Wo p t f o rb e n t o n i t e c o n t e n t s b e t w e e n 1 0 a n d 2 0 % i s p r e m a t u r e . F o r e x a m p l e ,t h e r e g re s s e d m i n i m u m Wop t v a l u e f o r t he S - G B m i x t u r e s o f 1 5 .1 %i s g r e a t e r t h a n t h e ,/ n e a s u r ed w o 0 t v a l u e s f o r t h e s a m e m i x t u r e sc o n t a i n i n g e i t h e r 1 0 o r 1 5 % o f g r a n u l a r b e n t o n i t e .

F i n a l l y, t he m e a s u r e d Wo p t v a l u e s f o r t h e S - G B a n d t h e S - P Bm i x t u r e s a r e p l o t t e d a s a f u n c t i o n o f t h e c o r r e s p o n d i n g m e a s u r e dP L v a l u e s i n F i g . 8 . A s e x p e c t e d , m o s t o f t h e d a t a a r e b e t w e e nt h e r e g r e s s i o n l i n e s b a s e d o n n a t u r a l c l a y s o i l s ( F i g . 6 a ) a n d t h ep u r e c l a y m i n e r a l s ( F i g . 6 b ) . H o w e v e r, n o s i m p l e l i n e a r c o rr e l a t io np a s s i n g t h r o u g h t h e o r i g i n i s a p p a r e n t . T h u s , e v e n t h o u g h t h e r ea p p e a r s t o b e s o m e c o r r el a t io n b e t w e e n Wo pt a n d P L t h a t m a yexpla in pa r t i a l ly th e in i t i a l dec rease in Wopt fo r the sand -ben to n i tem i x t u r e s e v a l u a t e d i n t h i s s t u d y, n o q u a n t i f i a b l e c o n c l u s i o n c a nb e m a d e i n t h is r e g a r d f r o m t h e r e s u l t s o f t h i s s t u d y.

E f f e c t o fC u r i n g P e r i o d

T h e s t a nd a r d c o m p a c t i o n c u r v e s ( A S T M D 6 9 8 ) f o r Te s t N o s .

1 3 - 1 8 ( s e e Ta b l e 5 ) , p e r f o r m e d t o e v a l u a t e t h e e f f e c t o f c u r i n gp e r i o d f o r t h e S - G B a n d t h e S - P B m i x t u r e s , a r e s h o w n i n F i g . 9 .C u r i n g p e r i o d r e f e r s t o t h e t i m e a l l o w e d b e t w e e n m i x i n g a n dc o m p a c t i n g t h e s a n d - b e n t o n i t e m i x t u r e s . T h e c o m p a c t i o n r e s u l t sf o r t h e o n e - d a y c u r i n g p e r i o d u s i n g M i x i n g P r o c e d u r e 1 a r e re p r e -s e n te d b y Te s t N o s . 6 - 8 f o r t h e S - G B m i x t u r e s a n d Te s t N o s .1 0 - 1 2 f o r t h e S - P B m i x t u r e s a s p r e v io u s l y p r e se n t e d . T h e c o m p a c -t i o n r e s u lt s f o r a s e v e n - d a y c u r i n g p e r i o d u s i n g M i x i n g P r o c e d u r e1 a r e r e p r e s e n t e d b y Te s t N o s . 1 3 - 1 5 f o r th e S - G B m i x t u r e s a n dTe s t N o s . 1 6 - 1 8 f o r t h e S - P B m i x t u r e s . T h e t r e n d s i n Wo p t a n dYdmax va lue s v e rsus ben to n i te con te n t fo r a l l o f these t e s t s a re

prese n ted in F ig . 10 .A s s h o w n i n F i g . 1 0 a , t h e g e n e r a l t r e n d o f d e c r e a s i n g Wo pt w i t h

i n c r e a s i n g b e n t o n i t e c o n t e n t f o r t h e s e v e n - d a y c u r i n g p e r i o d i s t h es a m e a s t h a t f o r t h e o n e - d a y c u r i n g t i m e . A l s o , e x c e p t f o r t h e S -

4 0

3 0Q .

e

O

2 0

EE0 . 100

Regression L ine-Natural Soils

. . . . . Regression Line - Pure ClayMinera l s

[ ] S a n d - G r a n u l a r B e n t o n i te ( S - G B )

S a n d - P o w d e r y B e n to n it e ( S - P B ) [ ]

0 1 0 2 0 3 0 4 0Plastic Limit, PL ( )

FIG. 8--Correlation between plastic limit and optimum water content

fo r sand-granular bentonite S-GB) and sand-powdery bentonite S-PB)mixtures evaluated in this study for a one-day curing period and MixingProcedure 1.



11/16

HOWELL ET AL ON CLAY SOIL MIXTURES 453

( a ) M i x i n g P r o c e d u r e 1 w i t h7 - d a y C u r i n g P e d o d

] - - - -1 ~ I . = = , t . . . . I . . . . . I . . . . . I . . . . I ~ ~/

~ 1 7 .0 ~::, ::~:::: ::~:. 'r--~-~.~.-. :- .- :-I 1 0 % G B ~................................... 108.3~ 1 6 .8 -~ ." . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. E] 15 % G B [L-~-107.0 _o.. . 16.6-~-:-:.-:~:~iiiEi:='~iEi'::i:::~::lt- ~ 2 0 go GB_____~1 0 5 7. ~ ~ . +----:--- ,:--+ ,r ~ . O .~

13. ~+~`+~-+~-`~,+`~=+-++~+t+~+~+-~+~`~-+ ~++t+~`~- ~+++~ r+~.~;+~`~.:L~+-+-+-+-+-+-+-~- U R ' . D. ~ ~- ' b -~ +~*4 ~ i~+~`~ ' ` +b~ '4 `~4 .~ - ~ ` '+*4~`P +~+~h~ '~ , +. - 1 6 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....... ....... . ; ; ~ ................................... ~......... ,. 1 0 3 . 2 ~

- + - + - - - + - . . p + - f - + - - - ~ + . . . p - .p .p . . f -1 .+ .p+ .p . .+ .~++ . l . . . p . I . - -+ .. +. -p .. p- + . .. . p . . . . . + .. +. .+ .. .. +p .+ .. - .+ .. .p - -= 1 6 .0 - : ~ + + + i- - , - . + ~ + + . .. .. .. .. .. .. .. .. . + . .. .. .. .. .101.9+.,,.~ . . ' t . . . . . . . - ; - . .+ .+ .+p + . . . p . . . . . . . . . ,

1 5 8 ~ + ~ ~ + ~ . . . + . , - . - . . . . - ,.- 1 O 0 a

---_1 5 . 6 ~ j ~ i i ~ ~ ' + ' *.................................................................... .: ~-9 9 . 4 =. , - . :~::: 1~:~+':~ ~L+~-~`++ +~+ .~'- '~..+.-~ ...'~..~ .~++-~.~+.~.~. .~+~'...~.~`~ . . . . . :: 3| . 'I ~ + + 1 ~ ' + ~ - - + - + t - - = + . - ~ - - ' t . . . 1 ~ . + - - + . ~ 1 . - - I . - - < + - - . ~ + * - 1 . - - + 4 . . . ~ o .....i...+.I++o..~. ++_ ..~ ,. . . . :~:: ~+ ~::~+. . +-+.. ~,-+ .++-.+` -`~+ .~+~+~+.~ ~..+~-.~.:y~.+-~- +...+.~-d~.1 >

k - - -- ~ + ` + ~ ` ~ = ` ` ~ + + ~ - ` ~ ` + ~ + + ' ~ . .' + ` ~ ' ~ * ` ~ . '~ ' ~ ' ` { ~ + ~ ` + + ~ 4 P. `` k ` ` d ~ ' ` ~ t ` + ~ - + , ' + . . . . . ~ -

c 15.2-~-p++,r.:-+r.+.... .. ~--~:. . . . . . . . . . . . . . . . . ~ . . . . . . . . . a a m c . , ,+ . . . . ~ . - p . . .. p + + + .. . p. + + ~_ . + H .p . + ~. . p_ ~ . +. ~ + .+ _ . p. . . ~ i ~- + - - + - . ~ + . . p - +- + * . * ; . - . p * * + +p + ~ . - p . + - p . +p + = p - + . . + . - + . . . . . ~ . . . . . . . . . ,

- ~ i ---~ = 9 5. 55 . ::::::::::::::::::::::::::::::::::1 ~t I=t ::::::::::::: ::::::::::::: :::::::::::::: :::::::::::::: :::::::::::::: ::::::: ~aA ,'~+ -r s I . . . . I I . . . . I | ~ O H I . i d l

5 1 0 1 5 2 0 2 5 3 0M o l d i n g Wa t e r C o n t e n t , w ( % )

( o ) M i x i n g P r o c e d u r e 2with

( b ) M i x i n g P r o c e d u r e 1with


1 0 9 . 51 0 8 . 31 0 7 . 0 o ~1 0 5 . 7104 .5 pY1 0 3 . 2 . ~1 0 1 . 9 . ~1 0 0 . 6 R99.4 -'=-c9 8 . 1 : 39 6 , 8 ~ '9 5 . 59 4 . 3

( d ) M i x i n g P r o c e d u r e 2with7-day Cur ing Per iod 7 -dayC u r i n g P e r i o d

1 7 9 J . . . . i . . . . i . . . . t . . . . i . . . . , t n a ~ J i t , . . . . 1 9 51 7 . 2 ~. ........... +-+-;-'-.-,-.,~--;---::,.J.:- ~-L........ ..... ...............~ 0 .:1:-,-.,..++...::1:-,-+.....+ ~-,__,_. -+ . . . . +' , .- = :t : ........ = . . . . . . . . . . . . . . . . . ~ ..................................... ...... . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . 1 7 0 ......... ........... ............ ........... ........... ............ . 1 8 3,, 1 7 .0 ~. -; . . . . . . _,. ,. .. .. .. .- .= . .. .. .. .. .. .. . I - - I - - 1 0 " / ,G B 1 ~ 1 0 8 .3 ~ .-~ ..~ . .. .. .. .. .. .. .. .. . ~ ~ . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ~ 0 .

. ~ - ' : : . ~ : E : . ' Z : = : . . - . ' : : . ' ~ . ' : . = . . ~ . 7 ~ . ~ . - t - ~ : . E + : - + * - ' : - ' ~ ' - ; * ' : - - ' : * ~ ~E 1 . .. .. .. .. .. .. .. .. .. .. ~ . . . . . . . . . * = 1 6 . 8 : : : : : : : : = . : : : : : : : . ~ : : . - " : : : : : : : . ~ : : ' : : : : : . ' : . ~ : : : : : : 1 0 7 . 0 o,. 6.8~_.~_.~...+..~ ......................l - E ] 1 5 % G B ~ . : .~ 1 0 7 . 0 C 21 6 .6 -L% '~--::::~==:--"z'--~:.. .. .. [ 20 */0 G B ~L--~..1 0 5 7

1 :~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ . : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : - - o .' - " 1 6 : - T ' ~ ' : - : : : : * : : :: : : ~ - : l - d : : : : :* = : : : : : : : * : : ~ : : : : * ' - '+ : : : : = t1 0 5 7 " - "

. . . . . . . . . . . . . . . . . . . . . . : r 1 6 . 1 0 4 . 5

~ ~ ~ 2 ~ - - ~ 1 6 2 - - , - . ~ : ' - ' : : ' = - ~ : - - ~ . . . . . . . . . . . . . . . . 1 0 3 . 26 . 2 - . ~ ..2~.- .~ ~ 10 3 .2 ~ "= =- =:~--~: ; : : "~="-~:"" 1

. . . . . . . . - ~ . - -~ :-= .:- ~-~ - . . . . . . . . ~ u ~ , a ) c , 1 6 .O - ~ ;-'-.:--; _ ::- '~ .-".-i~ .:-1 01 .9 "~. . . . . . . . . . . . . . . . . . . . . . . . . . . ~ . . . . . . . . . . . . . . . . 1 5 . 8 u ~ ' - ' ~ 7 . - ~ ] T l l : - ~ : : t : - + ~ , ~ - : = : : ~ : . ' r " - 1 0 0 . 6

_z -: . ::::.::.~.~.-_._.::.:.. 3+'~ ~E-.--:--.'--:-.-~.--~--= ---. .. ~' ' ~' -' :- E~.~ 15 .6 : :~ - : ; : - - t - ~ : : :~ -~ < .= i~ : - z : ~ . : :~ : ; :~ : 9 9 .4 :~ 1 5 .6 - ~: : E:E ? . . .. . .. . .. . .. . .. . .. . .. -~-~::L-..--_--~"..~ .=::-::~ .z .:..-'ii~- .4 c, = , . . . . . I - - - I - - 1 0 % P B | . . . . . . . . . . . . . . ~ . . . .. . . , , ,: 3 1 5 .4 - - ~_ ~ - - t= I - - - ~ . . . . . . . . . . . . . . . . . . . ~ . . . . 98 1 "~ '- ""~ , :== .. .~ .= :: :z :. r_ -+ .,z_. :: ::

:-~_.T_.~=- _~ - -~ -~ . . . . . . . . . . . . . . . . . . . . . . . . . . , ~ , , : :.~ ::.= -,:1 - - [3 - - 15 ' ~ P B ~ - : : : - r. - ,.L -= -m.~ : :: , , , , , , ~ '_ . . . = . _ : . z ~ . _ ~ _ ~ . z .~ . : ~ _~ . . .2 _ . T _ . ~ . . . . , . . 3 . ~ . r . . ~ : : ~ : : ~ ~ ; J ~ ~ - , - + + - ' ~ o - - + - - ~ ~ - + - - ~ - , ~ + - - ~ o~ " 1 5 . 2 - ~ - ~ : ~ - ~ ~ d _ ~ - - _ ~ . _ + . ~ - . ~ - ~ - ~ - 9 6 8 = o . - ....~-_~.~.~ - o n oL ~ g k ~ - ' - : - ~ . ~ - ~ : ~ . - U O .O

5 1 0 1 5 2 0 2 5 3 0 5 1 0 1 5 2 0 2 5 3 0Molding W ater Content , w ( ) Molding W ater Content , w( % )

F I G . 9 - - S t a n d a r d c o m p a c t i o n c u r v e s ( A S T M D 6 9 8 ) f o r s a n d - b e nt o n i te m i x t u re s b a s e d o n t w o d i ff e r e n t m i x i n g p r o c e d u r e s [ G B = g r a n u l a r P B = p o w d e r y b e n to n it e ]

GB mix tu re a t 20% ben ton i t e con ten t , the d i ffe rence in Wopr e s u l t i n g f r o m t h e d i f f e r e n t e u r i n g p e r i o d s f o r t h e s a m e s a n d -b e n t o n i t e m i x t u r e a n d b e n t o n i t e c o n t e n t i s l e s s t h a n ~ 0 . 5 p e r c e n t -a g e p o i n t s .

T h e t r e n d s i n t h e ~ /d m ax v e r s u s b e n t o n i t e c o n t e n t f o r b o t h t h eS - G B a n d t h e S - P B m i x t u re s s h o w n i n F i g . 1 0 b b a s e d o n t h e

s e v e n - d a y c u r i n g p e r i o d a r e e s s e n t i a l l y i d e n t ic a l t o t h o s e b a s e don the one -day c ur ing pe r iod . Also , the A~/dmax va lues r e su l t ingf rom the d i ffe ren t cu r ing pe r iod s fo r the same sand-ben ton i t e mix-tu re an d b en ton i t e con ten t a re -


12/16

454 GEOTECHNICALTESTING JOURNAL

- - -BI-- Sand-Granular Bentoni te (S-GB ) w / l -D ay C ur ing Per iod I- -O Sand-Granu la r Ben ton it e (S -GB) w/7 -Day Cur ing Pe riod I- A. - Sand-Pow dery Bentoni te (S-PB) w/ l -D ay Cudng Per iod- -z~-- Sand-Pow dery Bentoni te (S-PB) w/7-D ay Cudng P er iod I

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Clay So i l Con ten t (% )FIG. lO lnfluence of bentonite content on(a) opt imum water content

and (b)maximum dry uni t weight for Mixing Procedure 1 and two curing periods.

tu re wi th a seven -day cur ing per iod re la tive to the one-day cur ingperiod prev iously i l lustrated in Fig. 10a is consistent with respectto the different mix ing procedu res and, therefore, can be at tr ibutedpart ial ly to the difference in the curing periods.

Al though the t rends inWop an d 'Ydmaxversus bentoni te conten tshow n in Fig. 11 are consistent regardless of the mixing proced ure,som e differences in the Woptan d 'Ydmaxvalues based on the different

mix ing procedures a re apparen t . Except for the S-PB m ixture a t20% bentoni te conten t, the use of Mixing Procedure 2 cons is ten tlyresults in gre ater Wopt and ~/dmaxvalues than when Mixing Proce-dure 1 is used regard less of the type of bentonite . In addit ion, thegreatest differences in Wopt,o r A w o p tof 1 .9 percentage po in ts forthe S-GB mixture and 0.7 percentage points for the S-PB mixtureoccur a t the h ighes t b en toni te conten t o f 20% , w hereas the grea tes tA~dmax va lues of 0 .26 kN/m3 (1.7 pcf) for the S-GB mixture and0 . 1 8 k N / m3 (1 .0 pcf ) for the S-PB mixture occur a t the lowes tbentonite content of 10%. Both of these relat ive differences areconsistent with the expected effects of an increase in bentonitecontent on Wopt and 'Ydmax. How ever, the Awopt at 20% bentonitecontent and A~dma at 10% bentonite content are greater for theS-GB mixtures than for the S-PB mixtures. Thus, the part icle-sizedistr ibution of the bentonite in an air-dried condit ion apparentlyaffects the resu lts in Wopt and ~dmax at the relat ively h igh and the

relat ively low bentonite contents evaluated in this s tudy,respectively.

Except for the S-GB mixture wi th a 20% bentoni te conten twhe re the Awop is 1.9 percen tage points , the Awopt values due tothe two different mixing procedures (


13/16

H O W E L L E T A L . O N C L A Y S O I L M I X T U R E S4 5 5

- - I - - S a n d - G r a n u l a r B e n t o n i te ( S - G B ) w / M i x i n g P r o c e d u r e 1- - E l - S a n d - G r a n u l a r B e n t o n i te ( S - G B ) w / M i x i n g P r o c e d u r e 2- i - - S a n d - P o w d e r y B e n t o n i t e ( S - P B ) w / M i x i n g P r o c e d u r e 1- - zx - - S a n d - P o w d e r y B e n t o n i t e ( S - P B ) w / M i x i n g P r o c e d u r e 2

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1 7 . 0 - , ' - - - = - - ~ i - . . . . . . . ~ _ _ i . _ . ~ _ ~ . . . . ~ _ ~ . . . . _~ ~ . . . .i ' i ~ [ ' i i ' ~ " - q "4 - 4 - ~ - . - - + - I ~ - i - - ~ . - ~ -~ - ~ : - ~ : . . ~ L ~: - ~ - + . - ~ :t - ~ - - . - b - . p . - ~ - - . ~ - ~ . ~ - . + - + - + - - - . ' . . ~ - - q4 _ i - - ~. . " - . .~ . .. . __ p _

~ ; ; i i i i \ . ~ _ l t t I I - ' - ~ :. ,1 6 . 0 - ~ - - ~ - , - * - - - ~ - , . ~ - - * - - ~ - - ~ - ~ - - ~ - - ~ - - - ~ . . . . . ~ - -~ ' . . ~ . - = ~ . , = ~ - - ~ ~ F ~ - ~ - - ~ - ~ - - - - .- f - t ~ , , , - - 7 - - i " " - - - a , - . , - ~ - : - ~ I , ' - ~ - - i i - -. i i t i i i i ~ ~ L ~ Z ~ J _ L . _4 - -~ _ _ -- L -~ _ . ' _L _ L ._ . :

I : I f i i : ; : = l = : : :

1 5 . 0 . . . . . . . . . . . . . . . . . i- ~ - - - ~ - - . i - - - . , - - .,--- ; - 4 - - - ~ 4 - + - ~ , ~ - - ~ - I . . . . . . . . . . . . . . . . . . . .+ -q - - , ' . ~ q - - + - . - F - F - 4 - 1 ~ - + - ~ : { . ~ - - p . . . . . . . . . . . .~ -- F~ .- -- +- -~ -P.. -. ~- +. -- ~ ~ i ~ ~ - i i --~-~.--------:~ ~ - , ~ - - ~ - ..... , . . . . . .

. _ _ _ L . i i i : : . = , - r - : : - - - i - - - . k - - k - - F - - - i - - , , i i I ~ ' - - t ~ ' - . . . . . . . . .1 4 . 0 , ~ . . . . i , , . , ,- b " + - ~ F - . '- + - -+ - - 4 -. . . . ' - - ~ - - - ' ~ - , - - - - ~ + - ' - . -r ', -T-. . . . . . . . . . .J , -- -L - -L ~ .L . _ : ~ : : = l : = ~ - - : . = = ~ :

~ ' L ~ f i t ~ i : i i i t t ; l~ , . : : i/ i i f ' ' t : I i - - 7 7 " - ' ~ . i I i T l I - - ' :t ~ i . ~ i t i t i I t : : i i l:

1 3 . 0 1 - T - F - t ~ , , I ti I , i5 1 0 1 5 2 0 2 5

C l a y S o i l C o n t e n t ( % )

I , , , , I , , , , i , . , I , , , , I1 7 . 2 , , , , ~ __ ~ ~ , , , ~ , , ~ , , I t 1 0 9 . 5~- -SS- . _~ - ~ - l " - - , ~ - - ~ ' - - ' t - : ' t - - ~ . . . . . . .; - ~ . : . " r - t ~ ' T u1 - - - i - T ' T . . - - I ~ = " i ~ " -' " .- -" - ~ r 7 - - I - - ~ i " - r - - T - - F - % ~ ' t T- - ~ - - n - - - . - - - . i i ~ - v - - ~ - - - ~ - - ~ - - . -r - - -

~ . u ~ - " t - - T- ' ~ - T- - . - r - - , - - r - . , i ~ ' . 4 = i . ~ . ~ j ~ - - - r - - - ~ - - , , - - - ~ r - - - T - ~ u o . o ~ I1 i i ' | l ) - " t ' ~ l - , A ~ - = ~ - - I - - I i = ~ : ; " -~ 1

, o . o ~ ~ . V - f - : ? + " ~ - + - ~ , - - t - - ~ - : - + - + Iw . u. ~ ~ . - - ~ , - , , ~ : I ~ ~ - l - , - t ~ i ' - , - - ~ ~ - - - + - - +K l i .= ~ , , . - I - - - - ; - - - f - - . - + - - ~ - - - r - - - F - - = . ', I "; I - - . 4 - - - . i . - 4 - - - - - 4 - - ' ; - - - - i - . . - - I - , , , . , , . . . . ,

mo . o ~ - ~ - . - - ~ - - ~ . ~ , ~ . 4 - . 4 . - - .~ - - ~ + - - ~ , ~ - ~ - - i I- + - - i - - - 4 - - , . L . - . . t - -mu o . /~ - , , i . . . . . . - ~ - - ~ - . ~ - . r ~ . . . . - p - - ~ . ' ~ i " " . . . . ~ . - - 4 - . . - +1 i 1 i t .: ~ ~ i ~ ~ i l . , ' .: i #

l - - -. + -- l - -~ . . ,- ~ .. -- l - - - -~ - - e . . . . . t - . -+ - * - -~ - . . . . . - + ~l . - . - - - - - t - - - - - t . - - - - p . ' - - i . - - . = . . . - - - + . ' - - ~ - . l . - . - - ~ . . - . i . - - . - - t - - - z - - J . . . , , i . - . - i ~ i - - i . . . . . . . . ~b - . . . ~ . . : , . . - - + - . . . ~ . 4 - . . - - i . ~ . i . . . - . . - a . - - . i . - - ~ - . . . ~ . . t - - - ~ . - . i - . - = . . - - . ~ - -l - - . . i - - j ~ . L . . . J , _ ~ . - . . . . ~ _ . = _ L . . . r q . _ L . . i = r L . . . i . _ . ~ _ .~ .. .. .J L_ _.t - - V . -4 - -- F -- t- 4 _ :. 1 -~ - ;- ~ -- % - -- ~ ~ - - t ~ - : 4 - - ~ - - i _ _ 4 . . . .i l . i | : : = : 1 : 1 - - - - - ; , = :.l . . - - . ~ , - - . . . r - . - - . r . . . . ~ - - . . - - . . . ~ . - - . ~ _ . - _ _ i . - - , . ~ . . b _ _ . . ~ . . . _ t - - . - - . _ _ . i - _ . . ~ _ . - - : . . . . ..

l = = = ~ l I ~ t l : :

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FIG. 1 Inf luen ce o f bentonite content on( a ) opt imum water content and( b ) maxim um dry uni t weight for a seven day cur ing per iod an d twomixing procedures.



14/16

4 5 6 G E O T E C H N I C A L T E S TI N G J O U R N A L

l ' n m l e s l S i g n t f l c s a ee

T h e r e s u l t so f t h i s s t u d y i n d i c a t e t h a t d i f f e r e n c e s i n Wo p~ a n d' y/ m a x v a l u e s b a s e d o n l a b o r a t o r y c o m p a c t i o n o f s a n d - p r o c e s s e dc l a y s o i l m i x t u r e s c a n o c c u r d u e t o d i f f e r e n c e s i n t h e a m o u n ta n d t y p e o f p r o c e s s e d c l a y s o i l u s e d i n t h e m i x t u r e a s w e l l a s

d i f f e r e n c e s i n t h e c u r i n g p e r i o d a n d t h e m i x i n g p r o c e d u r e u s e dw i t h a g i v e n s a n d - c l a y s o i l m i x t u r e a t a g i v e n c l a y s o i l c o n t e n t .A l t h o u g h t h e d i f f e r e n c e s i n Wo p t a n d ' y/ m a x v a l u e s r e p o r t e d i nt h i s s t u d y a r e r e l a t i v e l y s m a l l i n m o s t c a s e s , t h e m a g n i t u d e s o ft h e s e d i f f e r e n c e s m a y b e s i g n i f i c a n t i n s o m e p r a c t i c a l a p p l i c a -t i o n s . F o r e x a m p l e , i n t h e c a s e o f c o n s t r u c t io n s p e c i f i c a t i o n sf o r c o m p a c t e d c l a y l i n e r s a n d c o v e r s t h a t r e q u i r e c o m p a c t i o na t a f i e l d w a t e r c o n t e n t , w ~ g r e a t e r t h a n o r e q u a l t o t h e o p t i m u mw a t e r c o n t e n t b a s e d o n l a b o r a t o r y c o m p a c t i o n ( i . e . ,wf >- WopO,a s m a l l d i f f e r e n c e i n Wo p t c a n h a v e a s i g n i f i c a n t e f f e c t o n t h er e s u l t in g h y d r a u l i c c o n d u c t i v i t y o f t h e c o m p a c t e d c l a y l i n e r.H o w e v e r, t h i s e f f e c t w i l l d e p e n d o n t h e s e n s i t i v i t y o f t h eh y d r a u l i c c o n d u c t i v i t y t o t h e c o m p a c t i o n w a t e r c o n t e n t w h i c h ,i n t h e c a s e o f t h e u s e o f s a n d - c l a y s o i l m i x t u r e s , m a y n o t b ea s s i g n i f i c a n t a s i n t h e c a s e o f n a t u r a l c l a y s o i l s ( e . g . , K r a u s

( a ) Ba t ch Mix ing P rocedure

- - - " " Q - "10%Clay Soil (5%A C+ 5% G B ) ~-]7- '~-' 1 6 . 2 ' ~ - - E l - 1 5%ClaySoi t (7 .5% AC + 7 .5% GB)_.~_

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t I t 1 i " i i ~ " ~ l " , i I . t .T '~ i i i i i i I i = . ,~~'- ,+ r' r-i- r '1-1 ~i--r'+'~*-~ * 'r-r-i-~ ~-r-~-r-r'+'~-r~,+. *-'~ ; 9 7 .4 ca

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e t a l . 1 9 9 7 ). N o n e t h e l e s s , t h e p o t e n t i a l s i g n i f ic a n c e o f t h is e f f e c tm u s t b e e v a l u a t e d o n a c a s e - b y - c a s e b a s i s .

S u r n n m r y a n d C o n c l u s io n s

T h e e x p e c t e d t r e n d s o f i n c r e a s i n g Wo p t a n d d e c r e a s i n g 'y dr na xw i t h i n c r e a s i n g c l a y s o i l c o n t e n t s f r o m 1 0 t o 2 0 % w e r e o b s e r v e df o r th e s a n d - a t t a p u l g i t e c l a y ( S - A C ) m i x t u r e s . H o w e v e r, f o r c l a ys o i l c o n t e n ts r a n g i n g f r o m 1 0 t o 2 0 % , Wo pt d e c r e a s e d w i t h i n c r e a s -i n g c l a y s o il c o n t e n t f o r b o t h t h e s a n d - g r a n u l a r b e n t o n i t e ( S - G B )m i x t u r e s a n d t h e s a n d - p o w d e r y b e n t o n i t e ( S - P B ) m i x t u r e s ,w h e r e a s ' yd m a x i n c r e a se d f o r t h e S - P B m i x t u r e s a n d r e m a i n e dr e l a t i v e l y c o n s t a n t f o r t h e S - G B m i x t u r e s . T h e r e l a t i v e d i f f e r e n c e sin these t r ends a re a t t r ibu ted , in pa r t , to (1 ) the g rea te r wa te rs o r p t i v i ty a n d l o w e r s w e l l i n g p o t e n t i a l o f a t t a p u l g it e c l a y r e l a t i v et o t h e t w o b e n t o n i t e s , ( 2 ) t h e l a rg e r p a r t i c le s i z e s o f t h e g r a n u l a rb e n t o n i t e i n t h e a i r - d r i e d c o n d i ti o n r e l a t i v e t o t h e p o w d e r y b e n t o n -i te , a n d ( 3 ) t h e p o s s i b l e c o r r e l a t i o n b e t w e e n t h e Wo p t a n d t h e P Io f t h e s a n d - b e n t o n i t e m i x t u r e s .

I n g e n e r a l , t h e t w o d i f f e r e n t c u r i n g p e r i o d s ( o n e - d a y a n d s e v e n -d a y ) c o n s i d e r e d i n t h is s t u d y h a d a s m a l l e f f e c t o n t h e Wo pta n d ' y / m a xv a l u e s f o r th e S - G B a n d t h e S - P B m i x t u r e s a t t h e s a m e c l a y s o ilc o n t e n t s a n d f o r t h e s a m e m i x i n g p r o c e d u r e , F o r e x a m p l e , t h e Aw o pv a l u e s a n d A 'y a~ na x v a l u e s r e s u l t in g f r o m t h e t w o d i f f e r e n t c u r i n gp e r i o d s w e r e ~ 0 . 5 p e r c e n t a g e p o i n t s a n d - < 0 . 0 8 k N / m 3 ( - < 0 .5 p e f )r e s p e c t i v e l y. H o w e v e r, t h e d i f f e r e n t c u r in g p e r i o d s d i d r e s u l t i n d i ff e r e n t t r e n d s i n 'y a m a x v e r s u s b e n t o n i t e c o n t e n t f o r t h e S - G B m i x t u r er e l a t i v e t o th e S - P B m i x t u r e s , p o s s i b l y d u e t o t h e d i f f e r e n t p a r t i c l es i z e d i s t ri b u t i o n s o f t h e t w o b e n t o n i t e s i n t h e a i r - d r i e d c o n d i t io n .

M i x i n g t h e s a n d a n d b e n t o n i t e i n a d r y c o n d i t i o n b e f o r eadd ing wa te r cons i s te n t ly resu l t ed in g re a te r Wopt and 'y /maxv a l u e s t h a n m i x i n g t h e s a n d w i t h t h e a p p r o p r i a t e a m o u n t o fw a t e r b e f o r e a d d i n g t h e b e n t o n i t e r e g a r d l e s s o f t h e t y p e o fb e n t o n i t e . H o w e v e r,th Aw o p v a l u e s t e n d t o b e t h e g r e a t e s t a tt h e 2 0 % b e n t o n i t e c o n t e n t , w h e r e a s t h e A ' y /m a x v a l u e s t e n d t ob e t h e g r e a t e s t a t t h e 1 0 % b e n t o n i t e c o n t e n t f o r a g i v e n s a n d -b e n t o n i t e m i x t u r e . A l s o , t h e d i f f e r e n c e i nWop a t 2 0 % b e n t o n i t ec o n t e n t a n d Y / m ax a t 1 0 % b e n t o n i t e c o n t e n t a r e g r e a t e r f o r t h eS - G B m i x t u r e s t h a n f o r t h e S - P B m i x t u r e . T h i s d i f f e r e n c eb e t w e e n t h e S - G B m i x t u r e s a n d t h e S - P B m i x t u r e s a g a i n i sa t t r ibu ted , in pa r t , to the d i ffe ren t pa r t i c le - s ize d i s t r ibu t ions o ft h e t w o b e n t o n i t e s i n t h e a i r - d r i e d c o n d i t i o n .

T h e m i x i n g o f t h e a t ta p u l g i t e c l a y a n d g r a n u l a r b e n t o n i t et o g e t h e r i n s m a l l a m o u n t s f o r e a c h in d i v i d u a l c o m p a c t i o n p o i n t f ot h e s a n d - a t t a p u l g i t e c l a y - g r a n u l a r b e n t o n i t e ( S - A C - G B ) m i x t u r e scons i s ten t ly resu l t ed in h ighe r ' ydmax and Wopt va lue s re la t ive to

m i x i n g t h e a t t a p u l g i te c l a y a n d g r a n u l a r b e n t o n i t e t o g e t h e r i n l a rga m o u n t s s u f f i c i e n t t o c o v e r a l l c o m p a c t i o n p o i n t s f o r t h e S - A C -G B m i x t u r e s . W h e r e a s t h e A 'y dm a x v a l u e s r e s u l t i n g f r o m t h e s e t wm i x i n g p r o c e d u r e s t e n d t o b e l o w[A ydm ax


15/16

H O W E L L E T A L , O N C L A Y S O I L M I X T U R E S 4 5 7

~ ~ ~ M ~ P ~ U ~I n d i v i d u a l M i x i n g P r o c e d u r e /

J ~ -~ . .. .. ; r I ' '4 ~ m , : : t ~ ~ | - - - . , .

-q.-- ] ~ . . . . .

. ~ * ~ : 1 : : : ~ . . ~ , , t t ~ - L - - 'P - _ ' ; l k - I I 4 - - . P - ~. . . . . . . .

1 7 5 . .. . , I ~ ; ' . ....

I / . u . L L _ L I I I - 4 : 4 : 1 l , , l I 1 ; M x . T- ' 4 - - - : ~ r ~ : . - :- ' . 'LZ P -

: - ' t - , . . . . . . . - - + - -

1 6 0 ' " ~ ~% - P z + . : - T - : : ~ ~ ~ ~ : : : : : . h : :

C l a y S o i lC o n t e n t ( % )2 5

a -

,,I L'~, .a 1 , I t * I * : II o .4 ~ L L ~ I . | l I I l : I I t I I1 1 3 4 . 4

= - , , , - , - , ' ~ - ' j : - ~ - i ' : - - - t - ~ . - - P - k - - - r - ~ : - 4 - - : : : - ~ - - - 4 - - ~ 1 0 3 . 7

16 .2 .k ~d . . . ._ ~ , _ ~ __ i_ \ ~ t t t ; . - - :- ~ -~- - -- - , -- - - -q. - - -4- - -+ ..~ i :: :~_~ ~"

1 0 3 1 - ~ ~ + - - ~ - - - ~ - - i - - 4 - - - ~ , - ~ - - ~ - . . . 4 - - ~m I ~ ~ ~ ' f .'~g_..2.z_.d._.d_ ~_._L_..2___L__: : : ID

~ , - - - ~ - ~ - ~ : = - r- -~ . . , , ~ -- 1 ' : ~ - - - + - ~ - 1 0 2 . 5I 1 : I | : l : : :~

~ 1 6 0 ~ ~ t - - h , ~ . . ~ - I - - P - P ; .--P--~---~--.--., ..... ~ . ,~ ~ 1 0 1 . 8

= : E

. ~ : - T ' - .T ' - i ~ i ~ - .~ . -k--k ~ -~ ~ - -~ . I I - -P-+--- : - -~ -- - -1 5 8 _ ~ , . T- - T- - r - - r - - t - ~ , - - r - - t - - r - r - ~ f - - - i - + - f . . . . . . p -

~ _ . . . . . , . . . . , , , ' . . , . . . . 1 0 0 . 6 ~ E5 1 0 1 5 2 0 2 5

C l a y S o i l C o n t e n t ( % )

FIG. 13--Influence of clay soil content on(a) optimum water content and(b) maximum dry unit weight fo r sand-attapulgite clay-granular bentonite(S-AC-GB) mixtures fo r a one-day curing peri od and two different mixing procedures.

a c k n o w l e d g e d . T h e o p i n i o n s e x p r e s s e d i n t h i s p a p e r a r e s o l e l yt h o s e o f t h e a u t h o r s a n d a r e n o t n e c e s s a r i l y c o n s i s t e n t w i t h t h eo p i n i o n s o f N S E T h e a t ta p u l g it e c l a y a n d g r a n u l a r b e n to n i t e s u s e di n t h i s s t u d y w e r e d o n a t e d b y t h e F l o r i d i n C o . , Q u i n c y, F l o r i d a ,a n d Wy o B e n , I n c . , B i l l i n g s , M o n t a n a . T h e s e d o n a t i o n s a r e g r a t e -f u l l y a c k n o w l e d g e d .

R e f e r e n c e s

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cal Engineering,ASCE, New York, Vol. 116, No. 1l, pp. 1641-1660.Garlanger, J. E., Cheung, E K., and Bishar, S. T., 1987, Quality Control

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Compaction of Sand-Processed Clay Soil Mixtures

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