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Comparison of Soil Suction and One-Dimensional Consolidation
Characteristics of a Highly Plastic Clay
Ser THl N2l_t2 n r . 2 h 5 e . 2 BI.DG
This publication is orre o{ a series of reports produced b y t h e D i v i s i o n o f B u i l d i n g Research,-National Research coun-cil of canada. No abridgement of this report may be published without the written authority of the Divieion. Extracts may be published for purposes of review only.
copies of this and other publications of the Division may be obtained by mailing the appropriate remittance (a Bank, Expresa, 9r Poet office Money order or a cheque made payabre at par in Ottawa, to the Receiver General of Canada, credit National Research council of Ganada) to the publications section, Divieion of Building Research, National Research
Council of Canada, Otta{va. Stamps are not acceptable.
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NATIONAL RESEARCH COUNCIL OT' CANADA DIVISION OF' BUILDING RESEARCH
COMPARISON OF SOIL SUCTION AND
ONE-DIMENSIONAL CONSOLIDATION CHARACTERISTICS OF A HIGHLY PLASTIC CLAY
by
D. G. tr'redlund
A l ' t
A L Y Z E D
Technical Papqr No. 245 of the
Division of Building Research
OTTArrifA JuIy 1967
PREFACE
As fine-grained soils above the water table are dried through processes of evaporation or plant transpiration, pore w a t e r p r e s s u r e s b e c o r n e i n c r e a s i n g l y n e g a t i v e with respect to atmospheric conditions. soils of high clay content extribit large volume change with change in moisture stress. In sub-h u m i d t o s e m i - a r i d c l i m a t e s , n e g a t i v e p o r e w a t e r s t r e s s e s calrse effective stresses on the soil solid phase that may be m u c h l a r g e r t h a n t h e s t r e s s e s i m p o s e d b y e n g i n e e r i n g
s t r u c t u r e s . c h a n g e s i n t h e s e s t r e s s e s a r i s i n g f r o m t h e s o i l climate are then of overriding importance in the long-term performance of foundations placed on such soils.
The purpose of this study was to compare the effects of one-dimensional consolidation caused by the application of load to the solid phase, with the shrinkage caused by a reduction of stress in the fluid phase. This report s u m m a r i z e s r e s u l t s p r e s e n t e d i n a n M . S c . t h e s i s by the author, entitled frComparison of Soil Suction and
One -dimensional Consolidation Characteristics of a
Highly Plastic C1ayt', presented to the Faculty of Graduate Studies, University of Alberta in May L964. Much of the field and laboratory work associated with this study was carried out by the author while employed as a summer assistant with the Division (at the NRC Prairie Regional station in saskatoon) during the summers of 1962 and 1963, and forrns part of a broad Divisional study of problems
affecting building foundations on volume changing clay s u b s o i l s .
Ottawa JuIy 1967
R . F . L e g g e t Director
r t
RESUME
La Division des recherches en b6.tirnent du NRC poursuit depuis plusieurs ann6es des recherches sur les caract6ristiques de retrait et de gonflernent des argiles forternent plastiques des Prairies. La difficult6 qulont l surrnonter les ing6nieurs de g6nie civil provient de lrabsence dtune rn6thode de calcul perrnettant drestirner ilampleur des ddplacernents verticaux dtun ouvrage 16ger. or a rnen6 h. bien une 16capitulation bibliographique des travaux de recherches r6alis6s en Angleterre, en Afrique duSud, en Australie, enrsradl, et aux Etats-unis, etune 6tude de deux rn6thodes de calcul propos6es, ltune par Ie groupe croney (L95zl, et lrautre par Jennings
( 1 9 5 7 ) .
Lrauteur a rnen6 b bien un prograrnrrle dressais pour Ia d6terrnination des caract6ristiques de succion de lrargile de la for -rnation Rdgina, et pour 6tablir une conlparaison entre ces 16sultats
et la courbe pression appliqu6e /tenear en burnidit6 que donnent les essais habituels de consolidation. Lrauteur rnontre que les courbes de pression-prirnitive/indice des vides, tant pour les eesais de con-solidation que pour ceux de succionaux environs du point de satu-ration, sont pratiquernent sirnilaires. Ltarlure des branches des courbes de pression/indice des vides concernant la recornpression sont tout ). fait diff6rentes pour les deux techniques.
COMPARISON OF SOIL SUCTION AND
ONE -DIMENSIONAL CONSOLIDAT ION CHARACTERISTICS
HIGHLY P],ASTIC C]-AY O F A
b y
D. G. Fredlund
ABSTRACT
Investigation of the shrinking and swelling action of highly plastic clays on the Prairie Provinces has been carried out for several years by DBR/WRC. The problern facing eugineers associated with the building industry is the lack of an analysis whereby the probable arnount of Vertical rnovement of a light structure can be predicted. A literature review of research work in England, South Afri.ca, Australia, Israel and the United States was
conducted and a study rnade of two analyses that have been developed; one by Croney et al (L952) and the other by J e n n i n g s ( I 9 5 7 ) .
A testing prograrn was conducted which involved the determination of rnoisture-suction characteristics of Regina Clay and a cornparison of these results with the rnoisture-pressure relationships obtained by the conventional
consoli-dation test. It was found that virgin pressure-void ratio curves are essentially the sarne for both consolidation and suction tests at close to full saturation. The curvatures of t h e r e c o l n p r e s s i o n b r a n c h e s , h o w e v e r , o f t h e p r e s s u r e - v o i d ratio curves for the two test techniques are quite different.
+ + + * & $ rr-T f + + ?F + 4t
I n r e c e n t y e a r s i n c r e a s i n g i n t e r e s t h a s b e e n s h o w n in the behaviour of highly swelling soil. Vertical rnovernents of engineering structures placed on the highly plastic lacustrine c l a y s i n W e s t e r n C a n a d a p o s e a s e r i o u s p r o b l e r n ( B a r a c o s a n d Mararrtz, 1952; Baracos and Bozozuk, 1957; Harnilton, 1963). The basic problern confronting foundation designers appears to be the lack of a rnethod of predicting the probable heave.
- 2
A considerable arnount of research on this problern has been conducted in various countries of the world. A
literature survey revealed two analyses that appear prornising. one was developed in England (croney et aI r95z') and is based on the results frorn a suction test and a shrinkage test. The other, developed in south Africa (Jennings 19571, is based on t h e r e s u l t s o f o n e - d i r n e n s i o n a l c o n s o l i d a t i o n t e s r s .
T h i s p a p e r d i s c u s s e s t h e s t r e s s e s a s s o c i a t e d with the swelling problern in the fierd and an assirnilation of these stresses in the laboratory. The rnajor point of investigation cornprises a cornparison of the soil suction test and the one-dirnensional consolidation test since it is these test results which have been used by other investigators to predict probable h e a v e .
STRESSES ASSOCIATED WITH THE SWELLING PROBLEM
Upward vertical rnovelnents often occur in tight structures as a result of the disturbance of the rnoisture regirne existing prior to construction. The arnount of rnoverrrent depends upon the difference between the initial and final equilibriurn water regirnes. The rnoisture regirnes are related to the relative irnportance of factors such as transpiration, evaporation, and infiltration" In areas where the clirnate is hurnid and the soil profile relatively wet, settlernent of a structure rnay occur due to a cut-off in the arnount of infiltration (Aitchison, l95l). In Western Canada where the clirnate is generally serni-arid, tran-spiration and evaporation give rise to a rnoisture-deficient soil profile. Evaporation and transpiration place a tensile stress on the water phase and thus increase the effective stress in the soil. Construction of a building, however, inhibits transpiration and evaporation and the net upward nrovelrrent of water results in a rnoisture gain. The rnoisture gain decreases the pore water tension and results in a volurne i n c r e a s e .
The distribution of stresses in the soil profile and the changes that can occur due to transpiration, evaporation, and infiltration have been clearly outlined by Jennings and K e r r i c h ( 1 9 6 2 I ( F i g u r e l ) " L e t u s assurne the case of a soil rrrass which is initially saturated, with a water table at a certain distance below the ground surface. tr'or the condition o f n o w a t e r f l o w ( F i g u r e l a ) , t h e p o r e w a t e r stress is negative, linear, and directry related to its height above the water table.
- 3
11""1"::^:"_",1
suction,, is widely used to designate the stress
ll^tl:^Y."
ph.as-e
and is defined as ,,the diffe"Lrr." between
::: ::_" ":",: "f
the s ur fac e f or c e s ;
"r;;;i;;;;r:;
"ff
;"= J";
structuret' (Croney et al, lgSZ!. o
tr'igure lb shows the new equ'ibriurrr pore-water pressure conditions if a constant evaporation is irnposed which is not large enough to cause the entry of air into soil rnass. the
Th
s h ip i s " t i 1r ri,, : a:,:' ;Ji[ : i"" ;; : l:; ""?ffj * :.1il : ?:.,"Jj
w a t e r p f e s s u r e rine. The increase in effective s t r e s s c a u s e s consolidation and thus a settrernent of the ground surface.As further evaporation and transpiratioa
by plants add to the tensile stress in the pore water, the effective 6 t r e s s i s g r e a t l y increased and the high tensire stress r n a y cause the so'to crack (Figure lc). ir."iog-.
right structure o n t h i s s o i l rnass increasu" tt. totar stress] The prevention of evaporation and transpiration, however, and the infiltration o f r a i n w a t e r results in a gradual decrease of pore-water tension'
a reduction in the effective stress, and a vorurne increase.
The vorurne change or the arnount of heave depends upon the rnagnitude of the inilial and final effective stress conditions in the soil rnass.
ICTION OF HEAVE
rdiction of total heave was l ) a n d i s b a s e d on the results e test. This analysis has Great Britain, India, and probable arnount of heave beneath asphalt and concrete roadways and airport runways ( R u s s a r n , lg62I.
The initiar soil conditions are rneasured in terrns of a water content profile- The final conditions are in terrns of an equiribriurn
water content profile based on an estirnated p o r e - w a t e r
s t r e s s p r o f i l e which is below atrnospheric pressure and a function of the distance above the water tabre. (The finar equilibriurn
water conditions are estirnated frorn the soil suction v e r s u s w a t e r content results. ) T h e s h r i n k a g e t e s t r e s u l t s are used to relate water contents io the specificiurk vorurne of the s oil"
+
-A n o t h e r a n a l y s i s w a s d e v e l o p e d by Jennings (195?)
and is based on the results of a rrfield or natural water contentrr c o n s o l i d a t i o n t e s t a n d a ' t f r e e - s w e l l t c o n s o l i d a t i o n t e s t .
The rrnatural water contentrr consolidation test is used to represent field conditions where load is applied to the soil without any other external influence to change the rnoisture r e g i r n e . T h e r r f r e e - s w e 1 1 1 ' t e s t i s u s e d t o e s t i r n a t e the final equilibriurn water content conditions under the applied load which acts as an irnperrneable covering over the soil. The arnount of heave is predicted by deterrnining the change in void ratio which occurs between the initial and final stress conditions in the field. Further research and rnodification o f t h i s p r o c e d u r e h a s b e e n r e p o r t e d by Burland (1962ll. THEORY
Since the two main procedures that have been used t o p r e d i c t h e a v e a r e b a s e d o n t w o different tests, it was d e c i d e d t o s t u d y t h e r e l a t i o n s h i p b e t w e e n the tests on a
typical volurne-changing clay soil frorn Regina, saskatchewan. There appears to be a definite rack of literature which deals specifically with this relationship. There is also the question of whether the suction test or the one-dirnensional consolidation test rnore closely parallels the conditions to which a soil is
subjected in the field such as transpiration, evaporation, infiltration, as well as changes in physical loading.
For clarity, the suction test theory is outlined in considerable detail since it is not found in present soil r n e c h a n i c s t e x t b o o k s . T h e p r o c e s s o f c o n s o l i d a t i o n h a s been explained by Taylor ( 19481 and others by reference to a rnechanical analogy using a piston and spring. A rnodification of their analogy is now proposed to represent t h e p r o c e s s o f c o n s o l i d a t i o n d u e t o suction stresses in the p o r e w a t e r i n s t e a d o f l o a d s a p p l i e d directly to the solid phase. The rnodified piston and spring analogy is shown in Figure 2. Consider two frictionless, tightty fitting pistons, one placed in the charnber and the other in the cylinder as shown. The piston in the charnber has a hole in it which represents a pore at the surface of a soil rnass. Initially, the stopcock at the bottorn of the charnber is closed to prevent the escape of water and a load is placed on the pan connected to the bottorn piston. The instant the stopcock is opened, water starts to rnove frorn the charnber into the cylinder and as both pistons sink, the load
)
-is taken up by the spring. The length of tirne required for the spring to take up the applied load depends upon the rate at which water escapes through the stopcock. 'when the piston stops rnoving, the load on the spring is equivalent to the stress in the water phase. It should be noted that the water rneniscus that forrns as part of the top piston has a radius of curvature which is a function of the tension applied to the water phase. The rnaxirrrurn tension that the water phase can develop is equal to the air entry value of the opening. Considering the case of a clay soil, the rnaxirnurn air entry value rnay be in excess of one atrnosphere, perhaps up to fifteen atrnospheres orf greater.
The changes in neutral and effective stresses during t h e t r c o n s o l i d a t i o n p r o c e s s r r i n a s u c t i o n t e s t are shown in Figure 3. Let us consider an undisturbed soil sarnple, the neutral and effective stresses of which are unknown. Initially, the sarnple is placed on the porous plate in the suction apparatus and allowed access to water until it cornes to equilibriurn under an applied suction. The total neutral and effective stresses are then known and are as shown in Figure 3a" Apprication of a new
suction incrernent does not alter the stresses throughout the sarnple, except at the drainage surface where the neutral stress g o e s t o - P 2 a n d t h e e f f e c t i v e s t r e s s to +P2 (FiSure 3b). As c o n s o l i d a t i o n p r o c e e d s , t h e e f f e c t i v e stress increases and the tension in the pore water increases a corresponding arnount (Figure 3c)" When the pore-water tension throughout the sarnple is equal to P2, the effective stress is also equal to P2 and the consolidation is coneplete. Several points about the suction test are noteworthy: the total stress is atrnospheric pressure throughout the consolidation process; after consolidation the water is in a state of tension; volurne changes are always of a thr ee -dirnensional natur e.
It should be noted that the laboratory testing prograrn w a s c a r r i e d o u t o n p r e s s u r e p l a t e a n d p r e s s u r e r n e r n b r a n e apparatus rather than on a true suction apparatus. The t h e o r e t i c a l d i f f e r e n c e b e t w e e n a t r u e s u c t i o n t e s t a n d a p r e s s u r e t e s t i s r e l a t e d t o t h e c h a n g e i n p r e s s u r e d a t u r n .
Lowering the stress in the water and leaving the surrounding a t r n o s p h e r i c p r e s s u r e c o n s t a n t ( a s i s d o n e i n a s u c t i o n test) is the sarne as raising the surrounding aft pressure in the cell and keeping the water stress at atrnospheric (as is done in a p r e s s u r e t e s t ) .
6
-C o n s i d e r i n g t h e p r e s s u r e p l a t e test, Figure 3 would rernain essentially unchanged. In either test the irnportant factors to rernernber in drawing stress diagrarns are that stress is being applied to the water phase only and that the flow gradient rnust initially be at the rrstopcockrt or point of drainage. The above e><planation refers only to a saturated soil rnass"
SOIL AND TESTING PROGRAM
The soil used for this testing prograrn was clay of high plasticity frorn the glacial Lake Regina sedirnent. It was obtained at elevation I866. I ft. , i. e. , L5.6 ft below t h e o r i g i n a l g r o u n d s u r f a c e o f I 8 8 1 . 7 5 f t . , f r o r n a test pit in the basernent excavation for the new Saskatchewan
Governrnent Telephones Building on the northwest corner of college Avenue and Albert st. , in Regina, saskatchewan. A surnrnary of the classification tests is shown in Table I.
A p r e s s u r e p l a t e e x t r a c t o r ( F i g u r e 4 ) and a pressure rnernbrane extractor (Figure 5) were used to obtain results in a pressure range cofirparable to that of the standard consolidation test. The pressure plate extractor had an operating range of 0 to 1 kg per sq crn. The specirnens
a r e p l a c e d o n a p o r o u s s t o n e o f h i g h air-entry. A i r p r e s s u r e is applied frorn above; the water beneath the stone is at a t r n o s p h e r i c p r e s s u r e ( R i c h a r d s et al, 1943I. The pressure rnernbrane extractor extends the operating range by rneans of a cellulose rnernbrane which has a very high air-entry v a l u e ( C r o n e y e t a l , 1 9 5 8 ) .
As part of this study, a new pressure plate apparatus was built which allows the rneasurernent of the rate of con-solidation (tr'igure 6). The perrneability of the porous stone is rnore than 100 tirnes greater than that of the soil and does not cause significant error in the deterrnination of rate of c ons olidation.
The testing prograrn involved the deterrnination of the soil suction versus water content relationship, and a cornparison of these results with those obtained frorn the standard one-dirnensional consolidation test. specific burk volurne was deterrnined during the suction test as well as during evaporation after the sarnples were rernoved frorn
7
-the suction test apparatus" All testing was perforrned on soil which was initially rernoulded at a water content near the liquid rirnit. The suction test sarnples were prepared by consolidating slurry in a one-dirnensional consolidorneter to various pressures after which they were rebounded to a token pressure. varying the consolidation pressures gave rise to the various initial water contents. Thus the stress conditions associated with the preparation of the suction and one-dirnensional consolidation test specirnens were the sarne.
DISCUSSION OF TEST RESULTS
T h e r e s u l t s o f t e s t s c a r r i e d o u t i n t h e p r e s s u r e p l a t e and pressure rnernbrane apparatus are referred to as soil s u c t i o n v a l u e s " T h e s e t e s t s , h o w e v e r , d o n o t r e d u c e t h e p o r e - w a t e r s t r e s s b e l o w a t r n o s p h e r i c b u t r a t h e r i n c r e a s e t h e s u r r o u n d i n g a i r p r e s s u r e a n d l e a v e t h e p o r e - w a t e r stress at atrnospheric pxessure. The difference is essentially one of technique and does not appreciably alter the test results ( P e n n e r , 1 9 5 9 ) .
Figure 7 shows the relationship between water content and logarithrn of soil suction for all suction tests perforrned on both the pressure prate and pressure rnernbrane extractors. The one-dirnensional consolidation results are shown in Figure 8 which is a plot of water content versus logarithrn effective
pressure. In cornparing the test results, it should be first noted that the one-dirnensional consolidation test induces anisotropic consolidation of the sarnple while the suction test causes isotropic consolidation, Cornparisons of the two p r o c e s s e s o f c o n s o l i d a t i o n ( A b o s h i a n d M o n d e n , I96I; Bishop and Henkel, 1962) have shown that rnore water is forced out of the soil during isotropic consolidation. The
difference in the arnount of consolidation occurring is explained in terrns of changes in the soil structure resulting frorn aniso-t r o p i c a n d i s o aniso-t r o p i c c o n s o l i d a aniso-t i o n . T h e s h e a r s t r e s s e s b e t w e e n the soil particles is lower in isotropic consolidation and perrnits lnore consolidation of the soil rnass. In the field, evaporation and transpiration are conducive to isotropic consolidation.
Cornparison of the suction and one-dirnensional consolidation test results shows their virgin cornpression
branches to be very sirnilar (Figure 9). when the consolidation curve was corrected for the corrrpressibirity of the filter paper and side friction in the consolidation ring, the curve appeared to fall directly on top of the suction curve for pressures up to
- 8
T h e r e a p p e a r s t o b e a d i f f e r e n c e i n t h e r e c o r n p r e s s i o n branches of the two curves (tr'igure 9). The suction test shows a srnoother curve with no distinct break in curvature at the point w h e r e t h e p r e c o n s o l i d a t i o n p r e s s u r e i s e x c e e d e d . I n a d d i t i o n , the suction results have lower water contents than the one-dirnensional consolidation results on the recornpression branch. The difference in the two curves is probably related either to t h e s t r u c t u r a l r e s i s t a n c e s a n d s h e a r i n g s t r e s E e s a s s o c i a t e d with isotropic and anisotropic consolidation or to the effect of side friction in the consolidation rings.
J e n n i n g s ( 1 9 6 0 ) a n d A i t c h i s o n ( 1 9 6 0 ) p r o p o s e d r h a t a point would be reached on the virgin cornpression branch where the suction and consolidation results separate. This point was believed to coincide with the cornrrlencernent of air
entry into the sarnple. Figure l0 shows the relationship between specific bulk volurne and water content as sarnples o f R e g i n a c l a y w e r e d r i e d , f i r s t i n t h e p r e s s u r e p l a t e e x t r a c t o r and rater by evaporation, Specific bulk volurne is herein defined as the volurne in cubic centirneters occupied by one hundred grarns of rnoist soil. Figure 11 shows the degree of saturation versus water content for the sarne sarnples. On the basis of the test results, it can be predicted that the curves should begin to diverge at a water content of approxirnately 25 per cent, with the one-dirnensional consolidation curve going below the suction curve. The classification tests showed the plastic limit to be 25 per cent. The soil suction at this point would be approxirnately l6 kg per sq crn. The conventional effeclive stress equation for a two-phase systern wiII not hold below this water content as the soil then constitutes a three-phase systern.
In the analyses previously reviewed for the prediction of heave, the suction and the free swell test were used to
estirnate the final equilibriurn conditions. Since the test results appear to be essentially the sarrre, either analysis should give the sarne equilibriurn conditions up to the air entry value of the soil. The rnain discrepancy would occur in the recofirpression range of the curves.
The rate of consolidation for Regina clay in the suction tests and in the one-dirnensional consolidation test are next cornpared. Figure l2 shows the coefficient of consolidation versus soil suction and effective pressure for the suction and one-dirnensional consolidation tests. In all cases, the load incrernent ratio was approxirnately I. since several of the
- 9
factors affecting the coefficient of consolidation are equal in both tests, it is advantageous for the sake of clarity to plot pressure versus tirne to 50 per cent consolidation for a corrected length of drainage path. Figure I3 shows the plot of tirne to 50 per cent consolidation versus effective pressure for a corrected drainage length of 1 crn. The results show that at very low effective pressures (approxi-rnately 0. I kg per sq crn) the tirne to 50 per cent consolidation for both types of tests is sirnilar. At higher effective pressures the suction test requires rnuch longer tirne for 50 per cent
consolidation.
CONCLUSIONS
The following conclusions have been reached in this inve stigation:
1. The virgin cornpression branch of the suction and the one-dirnensional consolidation test results are essentially t h e s a r n e i n t h e p r e s s u r e r a n g e t e s t e d .
Z" The recornpression branch of the suction test shows no distinct break in curvature at the preconsolidation pressure. At a given stress within the recompression range the equilibriurn rnoisture content in the suction test is lower than in the conventional c o n s o l i d a t i o n t e s t . T h i s d i f f e r e n c e i s b e l i e v e d t o b e a r e s u l t o f s t r u c t u r a l r e s i s t a n c e t o r e c o r r l p r e s s i o n d u e t o shearing stresses and/or side friction in the consolidation ring.
3. When Regina clay is dried frorn a slurried condition the soil rernains saturated to a water content near the plastic lirnit which corresponds to a soil suction of approxirnately
16 kg per sq crn" At rnoisture contents lower than the plastic Iirnit, air invasion takes place resulting in partial saturation. At this and lower rnoisture contents the suction and the one-dirnensional tests are not cornparable.
4. The rate of consolidation appears to be different in the suction test than in the one-dirnensional consolidation t e s t . A t l o w l e v e l s o f e f f e c t i v e s t r e s s ( i . e . b e l o w 0 . 15 kg Per sq crn) the rate in the forrner is greater than in the latter. A t h i g h e r s t r e s s l e v e l s t h e r e v e r s e is true with the difference in rate increasing at higher effective stress levels. The plot of consolidation tirne to 50 per cent consolidation versus effective pressure shows the tirne to be longer in the suction t e s t w i t h a g r e a t e r d i f f e r e n c e w i t h i n c r e a s i n g pressure. T h e low effective pressure range should, therefore, be further investigated.
- l 0
ACKNOWLEDGMENTS
The authorts interest in the shrinking and swelling behaviour of highly plastic clay soils was stirnulated during surrrlner ernployrnent with the National Research council 0f canada at the Prairie Regional Laboratory in saskatoon, Saskatchewan.
He wishes to acknowledge the guidance and assistance given during the study and in the preparation of this report by Mr. J. J. Harnilton of the Division o1 Building Research and Dr. S. Thornson of the Civil Engineering Departrnent,
- 1 1 REFERENCES
Aboshi, H., and H. Monden, 1961. Three Dirnensiol2| Consolidation of Saturated Clays. Proc. 5th Int. Conference of Soil
Mechanics and Foundation Engineering.
Aitchison, G. D. , I960. Relationship of Moisture Stress and Effective Stress Functions in Unsaturated Soils. Pore Pressure and Suction in Soils, London, Butterworths" A i t c h i s o n , G . D . , a n d J . W " H o l r n e s , 1 9 6 1 . S u c t i o n P r o f i l e s
in Soils Beneath Covered and Uncovered Areas. Proc. 5th Int, Conference on SoiI Mechanics and Foundation Engine ering.
Baracos, A", and O" Marantz, L952. Vertical Ground Movernents. Proc. 6th Canadian Soil Mechanics Conference of the
Associate Cornrnittee on Soil and Snow Mechanics,
National Research Council Tech. Merno. 27, p. 29-36. Baracos, A., and M. Bozozuk, 1957. Seasonal Movernent in
Sorne Canadian Clays. Proc. of the 4th Int. Conference on Soil Mechanics and Foundation Engineering, London, V o I . 3 , p . 2 6 4 - 8 .
Bishop, A. W. , and D.J. Henkel, 1962. The Measurernent of Soil Properties in the Triaxial Test. Edward Arnold (Publishers) Ltd. Second Edition.
Burland, J. B. , 1962. The Estirnation of Field Effective Stress and the Prediction of Total Heave using a Revised Method of An'aLyzing the Double Oedorneter Test" Die Sivielle Ingenieur in Suid-Afrika, JuIy 1962.
C r o n e y , D " , J . D . C o l e r n a n , a n d P . M . B r i d g e , L 9 5 2 " T h e S u c t i o n of Moisture Held in Soil and Other Porous Materials.
Road Research Tech. Paper No. 24, H. M. Stationary Office, London"
Croney, D. , J. D. Colernan, and W. P. M. Black, 1958. Movernent and Distribution of Water in Soil in Relation to Highway Design and Performance. Water and its Conduction in Soils, Highway Research Board, Special Report No. 40.
t z
Fredlund, D. G. , L964" Cornparison of Soil Suction and
One-Dirnensional copsolidation characteristics of a Highly
Plastic Clay. MoSc Thesis, University of Alberta, Edrnonton, Alberta.
Harnilton, J. J. , 1963. volurne changes in undisturbed cLay Profiles in western canada. canadian Geotechnical Journal, Vol. l, No. I.
J e n n i n g s , J . E . B " , and K. Knight, lg57. Discussion by G. W. Donaldson and C. M. A. de Bruijn of ilThe Prediction of rotal Heave frorn the Double oedorneter Test. tt Syrnposiurn on Expansive Soils, Trans. of the South African Institution of Civil Engineers.
J e n n i n g s , J. E., I950. A Revieed Effective stress Law for use in the Prediction of the Behaviour of unsaturated soils. P r o c e e d i n g s of the conference on pore pressure and
Suction in Soils, Butterworths, London.
J e n n i n g s , J. E., and J. E. Kerrich, 1962. The Heaving of Buildings and the Associated Econornic consequences, with Particurar Reference to the orange Free state
Goldfields. Die Sivielle Ingenieur in Suid-Afrika.
Penner, E., 1959" Soil Moisture Suction - Its lrnportance
and Measurernent, National Research council, ottawa,
Technical Paper No. 76.
R i c h a r d s , L. A. , and M. Firernan, Lg43. pressure plate Apparatus for Measuring Moisture Sorption and Transrnission by Soils. Soil Science.
Russarn, K., 1962. The Distribution of Moisture in Soils
at Overseas Airfields. Road Research Tech. paper
N o . 5 8 .
T a y l o r , D . W. , 1948. Fundarnentals of SoiI Mechanics. John Wiley and Son, New york, N. y.
TABLE I
SUMMARY OF CLASSIFICATION TESTS ON REGINA CLAY
T E S T RESULT Specific Gravity Atterberg Lirnits Liquid Lirnit Plastic Lirnit Shrinkage Lirnit Plasticity Index Grain -size Distribution*
S a n d S i z e s S i l t S i z e s C l a y S i z e s
Mineralogical Cornposition of Material Iess than 2 rnicrons**
Montrnorillonite Illite
Kaolinite Exchange C apacity{.*at
(rnilliequivalents per 100 grarns dry weight of soit).
Exchangeable Cations Magnesiurn Calciurn Potassiurn Sodiurn
2 . 8 3
7 5 . 5 2 4 . 9 1 3 . I 5 0 . 6%
To
%
To 8 Y o 4 L % 5t o/o o/o%
%
7 7
t 5
I 3 L . 7 r n e / I 0 0 g r n I 5 . 3 r n e / I o O 54. 4 rne/t OO 0 . 5 9 r n e / t o o I . 7 7 r n e / t O } grn grn grn grn * M . I . T . G r a i n - s i z e S c a l e:** X-ray Analysis perforrned by Alberta Research Council :F** B;<gtrange capacity analyses perforrned by the Soil Science
Departrnent, University of Alberta
Specific gravity, Atterberg lirnits, and grain sLze are the average of three sets of tests; X-ray analysis and exchange capacity were perforrned on one average sarnple" N O T E :
+
T o t a l
st r e s s
T o t a
I
s t r e s s
{ a ) N o e v a p o r a t i o n
f r o m s u r f a c e ( b ) W i t h e v a P o r a t i o n
s m a l l e n o u g h
t h a t n o a i r e n t r Y o r c r a c k i n g
o f t h e s o i
l o c c u
r s
Z o n e o f
s e a s o n a l
I m p e r
m e a b l es u r f a c e lo a d
i n f l u e n c e
T o t a
I o v e r b u
r d e n
p r e s s u r e
v e r b u r d e n
F i n a l e q u i
p o r e w a t e r
l i b r i u m
p r e s s u r e Plus
p r e s s u r e d u e
t o s u r f a c e lo a d
p r e s s u r e
( c ) E v a p o r a t i o n
l a r g e e n o u g h to c a u s e a i r e n t r y a n d c r a c k i n g o f t h e s o i l
F I G U R E I
S T R E S S E S
A C C O M P A N Y I N G
T H E D R Y I N G
A N D C O V E R I N G
O F A S O I L M A S S .
( A f t e r J e n n i n g s a n d K e r r i c h , 1 9 6 2 )
+l n p a r t i a l l y '
s a t u r a t e d
s o i l
( p o r e w a t e r
a n d
p o r e a i r s t r e s s l
8 e 3 t t 1 - tTop
piston
Water
meniscu
Bottom
piston
FIGURE 2
SUCTION
TEST - PISTON AND
Chamber
Cylinder
ANALOGY
8 P 3 8 3 4 - 2
TOTA
L
0
N E U T R A L
- P , 0
t h e
E F F E C T I V E
O P
a p p l i c a t i o n
o f a n e w p r e s s u r e
P,
a f t e r t h e a p p l i c a t i o no f a p r e s s u r e
( a ) Just prior
0
b ) T h e i n s t a n t
i n c r e m e n t
t o
- P ' 0
- P 20
0
.-q 0
0 r P ,
- P 2c ) A f t e r p a r t i a l c o n s o l i d a t i o n
( d ) After complete
c o n s o l i d a t i o n
N o t e : D r a i n a g e
a t b o t t o m
o f sample
o n l y
F I G U R E J
S T R E S S
C H A I ! G E S
D U R
I N G T H E C O N S O L I D A T I O N
P R O C E S S
I N A S U C T I O N
T E S T
0
I P 3 8 J 4 - 3M e r c u r y
r n a n o m e t e r
L o w p r e s s u r e
r e g u l a t o r
( w a t e r lread
b u b b l e r )
A i r
p r e s s u r e
r e g u la t o r
I
P r e s s u r e
r e l e a s e
( b } PRESSURE
P L A T E
E X T R A C T O R
D r a i n s
R u b b e r s t o p p e r
V e r t i c a l s u p p o r t b a r
D r a i n s
C l i l ; s
N e o p r e n e
r u b b e r
d i a p h r a g m
B u r e
v a l v e
( a ) ASSEMtsLY
O F P R E S S U R E
P L A T E
E X T R A C T O R
S o i l s a m p l e
P r e s s u r e
C e r a m i c
i n le t
p l a t e s
F I G U R E 4
8 p J 8 3 4 - 4l n l e t v a l v e
B y - p a i s
P r e s s u r e
m e m b r a n e
e x t r a c t o r
C o n n e c t i n g
h o s e
P r e s s u r e
r e g u l a t o r
C e l l u l o s e
m e m b r a n e
0 u t f lo w
w a t e r
f r o m s o i l
M i c r o s c o p i c
p o r e s
N it r o g e n
t a n k
M e r c u
r y
d i ff e r e n t i
a I
r e g u l a t o r
( a I ASSEMBLY
O F P R E S S U R E
M E M B R A N E
E X T R A C T o R
S o i l p a r t i c l e s
P r e s s u r e
i n c h a m b e r
S u p p o r t
s c r e e n
0 u t f lo w
t u b e
W a t e
r
f i l m s
( b ) S E C T I O N
V I E W O F E X T R A C T I O N
P R O C E S S
F I G U R E
5
P R E S S U R E
M E
M B R A N E
E X T R A C T O R
8 F 3 8 3 4 - 5P r e s s u r e
c h a m b e r
P r e s s u r e g a u g e
P r e s s u r e
r e g u l a t o r s
P r e s s u r e
s u p p l y li n e
( a )
A S S E M B L Y O F N E W P O R O U S
P L A I E A P P A R A T U S
6 s m a l l b o l t s
L u c i l e c a p
R u b b e r
s e a
I
* - G l a s s
p r e s s u r e c h a m b e r
S o i l s a m p l e
P o r o u s p l a t e
D e - a i
r e d w a t e r
S t o p c o c k
N E W P R E S S U R E
P L A T E
A P P A R A T U S
T o p r e s s u r e
s u p p l y li n e
i
( b )
F I G U R E 6
8 P 3 A 3 4 - 6N o t e : N u m b e r s i n b r a c l i e t s r e f e r t o p r e c o n s o l i d a t i o n p r e s s u r e i n k g / c m l 8 0 ( 0 . 0 6 2 ) o t 0 . 2 5 1 z. u c) n l o L! o_
A o o
F z. (-) EH 5 0
= ( 0 . 5 0 ) 1 2 . 0 1 ( 4 . 0 ) 4 0 0 . 0 1 0 . I 1 . 0 S O I L S U C T I 0 N , k g / c m 2 V E R S U S W A T T R C O N T E N I F O R R E M O L D E D R E G I N A C L A Y l 0 F I G U R E i S O I L S U C T I O N a P J e J l - 7( 0 . 0 6 2 ) N o t e : N u m b e r s p r e c o n s o l i d a t i o n i n b r a c k e t s p r e s s u r er e f e r
i n k g / c m 2
t o
8 0 ( 0 . 2 5 ) o -z U C) 7 n E -U o-;3 o o
z. O (-) v. - 5 0 = ( 0 . 5 0 ) 0 . 0 I F I G U R E 8 T F F E C T I V E P R E S S U R E V E R F R O M O N E - D I M E N S I O N A Lt . 0
P R E S S U R E , k g / c m 2 a 0 . 1 E F F E C T I V E S U S W A T E R C O N T E N T F O R C O N S O L I D A T I O N T E S T S 8 P 3 A 3 4 - t R E M O L D E D R E G I N A C L A Y D E R I V E D( 0 . 0 6 2 - - - - S u c t i o n te s t r e s u l t s - 0 n e - d i m e n s i o n a l c o n s o l i d a t i o n r e s u l t s t 0 . 2 5 1 ( 0 . 5 0 ) p r e c o n s o l i d a t i o n p r e s s u r e
______il
( 2 . 0 ) ( 4 . 0 ) 9 0 8 0 F z. lrJ o 7 0 E U o-= 6 0 L|J F z <> q) c e 5 0 t d = 4 0 3 00 . 0
r
0 . 1 S O I L S U C T I O N A N D E i T T C T I V g R E C O M P R E S S I O N B R A N C H E S T E S T S F O R R E G I N A C L A Y 1 . 0 P R E S S U R E , k g / c m 2 F O R S U C T I O N A N D O N E - D I M E N S I O N A L l 0 F I G U R E 9 C O M P A R I S O N O F C O N S O L I D A T I O N a P ' A J 1 - 9crl
o
O E. UJ o-(J (J uJ = O 6 CJ LL ; UJo-a
140
120
r00
60
80
40
40
R E IO
IFIC BULK VOLUME
N A C LA Y
8 P 3 8 3 4 - t o
WATER
CONTENT,
PER CENT
60
80
I00
FIGU
SPEC
R EG I
Evaporation
plate
Pressure
extractor
/
Saturation line
o^64o-e-' /,t / o o I I I I I o a ,, o o o o E v a p o r a t i o n I C J z U t o 8 0 E U
