Ge 440106

Tin& C. M. R., Sills, G. C. & Wijeyesekera, D. C. (1994). Ghotechnique 44, No. 1, 101-109

Development of KO in soft soils

C. M. R. TING*, G. C. SILLSt, and D. C. WIJEYESEKERAf

This Paper presents observations of the develop ment of K,, the coefficient of lateral earth pressure at rest, in a soft kaolin undergoing one-dimensional consolidation up to 150 kPa. A consolidometer with flush diaphragm transducers was linked to a system controlled by micro- processor for controlled gradient consolidation. Remoulded and artificially sedimented samples of kaolin in distilled and sea water chemistry were used in the experimental programme. Experimen- tal observations indicate that K,, is not a constant but varies linearly with void ratio. It is suggested that the traditional empirical correlations between K, and friction angle + may be applicable at low stress levels, given that $ may be higher at low effective stress levels than at higher values.

KEYWORDS: clays; consoldation; earth pressure; laboratory tests.

Larticle pr6sente des Ctudes de la dktermination de K, , coefilcient du poids lateral des terres au repos, pour un kaolin mou soumis i une consolidation unidimensionnelle pouvant atteiodre 150 kPa. LJn consolidom&tre, P capteurs ii diaphragmes afileu- rants, a et& relii! zi un sysdme pilotb par un micro- processeur permettant de contrBller le gradient de consolidation. Des &hantillons de kaolin remariirs et artificiellement sCdiment&s dans de Ieau distillb et dans de leau de mer ont &ti! utili&s dans le programme expbrimental. Les r&ultats exp&imen- taux montrent que K, nest pas constant et quil varie linbairement avec lindice des vides. II semble que les corritlations empiriques traditionnelles entre K,, et Iangle de frottement $ peuvent exister pour de faibles niveau de contrainte si lon suppose que $I est plus grand pour les faibles contraintes effec- tives que pour les contraintes plus elevbes.

INTRODUCTION

The significance of the horizontal effective stress in geotechnical analysis is increasingly being rec- ognized in modern geotechnical theories such as critical state theory, where the mean normal stress plays an important role in describing the stress history of the soil and in the analysis of its behaviour. Field instruments such as the cone penetrometer, the pressuremeter and the dila- tometer are influenced largely by the horizontal in situ stress, and may provide a way of measuring its value. The particular condition of zero lateral strain may often be assumed to exist in a soil foundation before the application of a load or construction of a slope. The horizontal effective stress in this condition can be related to the vertical effective stress by a parameter K, (defined as the ratio of horizontal to vertical effective stress in an element of soil under zero lateral strain). The value of K, is found to be related to the soil itself and to the stress history. It is therefore an

Manuscript received 15 December 1992; accepted 29 March 1993. Discussion on this Paper closes 1 July 1994; for further details see p. ii. * Travers Morgan Consulting Engineers. 7 University of Oxford. f: University of East London.

important parameter in the design and analysis of earth retaining structures, piles, slope stability and so on. However, information on the development of K, in soft soils is limited by the difficulty of sample handling and measurements under the strictly defined condition of no lateral deformation.

Nevertheless, there are published research measurements of K, with various methods chosen to provide the zero lateral strain condition. These methods fall into two distinct classes. The first uses a rigid lateral boundary (consolidometer type) which provides the required lateral strain condition, but also allows undefined friction between the wall and the consolidating soil. The second uses a flexible lateral boundary with feed- back systems to maintain the position of the boundaries (triaxial type). The advantage of this is that there is no side friction, but the disadvan- tage is that the best that can be achieved for the soil sample is zero mean lateral strain.

Within these two classes of experimental conditions there is a wide range of approaches. Newlin (1965) and Edit & Dhowian (1981) used strain gauges on the thin oedometer wall. Brooker & Ireland (1965) and Singh, Henkel & Sangrey (1973) developed a system of null strain condition by regulating the hydraulic pressure behind a thin

101

102 TING, SILLS AND WIJEYESEKERA

oedometer wall. Davis & Poulos (1963) and Lewin (1970) developed the controlled volume triaxial apparatus, in which the volume of the cell fluid surrounding the sample was maintained constant and hence it was presumed that the diameter of the soil sample remained unchanged. Bishop (1958), Moore (1971) and Menzies, Sutton & Davies (1977) used a conventional triaxial apparatus with various lateral strain devices to measure and regulate the cell pressure for zero lateral strain condition. Abdelhamid & Krizek (1976) used flush diaphragm transducers in a rigid consolidometer for lateral pressure measurement.

Since the publication of Jakys (1944) paper on the theory of K,, many researchers have suggested empirical or semi-empirical correlations of K, with the angle of shearing resistance 4 for normally consolidated soils. These relations are summarized in Table 1, which also gives the values of K, calculated for 4 = 22, appropriate for kaolin, for example. This Paper reports K, measurements made on very soft kaolin samples in a consolidometer under controlled gradient consolidation, with measurement of horizontal stress by a transducer mounted flush in the wall of the cell, and examines the results in the light of these correlations.

EXPERIMENTAL PROGRAMME Controlled gradient consolidation test

Lowe, Jonas & Obrician (1969) developed the controlled gradient consolidation test to provide two main advantages over the conventional step loading test. The rate of strain can be set to lower values, closer to those experienced in field conditions, without unduly increasing the length of the test. In addition, the pore-pressure gradient can be set sufficiently low to provide a distribution of effective stress across the height of the sample that is close to uniform. The sample therefore

remains in a reasonably uniform condition throughout the consolidation process, and a reli- able estimate of K, can be obtained from measurements of the pore pressure distribution and the horizontal and vertical total stresses.

Consolidation cell The rigid consolidation cell developed for this

programme was made from a Perspex tube of 4 mm thick wall, prestressed by a 10 mm wall thickness outer aluminium casing. The inner Perspex lining provided a good low-friction surface; the aluminium provided a stiffer lateral constraint. The radial strain of the cell under a maximum lateral stress of 200 kPa is calculated, based on elasticity theory of a thick composite cylinder, to be less than 2.0 x 10e5. This strain is considered small and is unlikely to affect the K, state of a soil during consolidation. Both the top piston and the base pedestal were grooved with circular and radial channels for drainage. A 3 mm thick Perspex plate, containing over 400 2 mm drilled holes, was placed above the base pedestal, with filter paper in place above it. A similar Perspex plate and filter paper arrangement was used beneath the top piston. The 104 mm dia. cell is 50 mm high and is equipped with strain-gauge- type pressure transducers which measure the top and base vertical total stresses, mid-plane horizontal total stress, and mid-plane and base pore- water pressures. The upper surface of the sample in contact with the loading piston is the drainage boundary. The cell is shown in Fig. 1.

Transducers The vertical total stresses are measured directly

by two flush diaphragm transducers (Druck PDCR-lOF, 300 kPa range) located at the top and base of the soil sample. Two transducers were used for measurement of the base pore pres-

Table 1. Summary of &-I$ correlation and K, values for kaolin

K, equation Reference

K, = 1 - sin 4 Jaky (1948)

K, = O-9 (1 ~ sin 4) Jaky (1944), Fraser (1957)

K, for kaolin (& = 22)

O-63

0.56

K 0

= (1 + i sin @)(l - sin 4)

1 + sin f#~ Jaky (1944)

K, = tan 45 - 1,15(& - 9) Rowe (1957),

0.59 2 Abdelhamid & Krizek (1976)

K, = 0.95 - sin 4 Brooker & Ireland (1965) 0.58

K, = 1 - sin (1.2@)(OCR) I w) Schmidt (1967) 0.56

DEVELOPMENT OF K, IN SOFT SOILS

Piston total stress transducer

Bleed valve I Upper drainage port

103

Horizontal total

Base total 3 stress transducer

Base pore-pressure total and differential

Mid-plane pore-pressure transducer

Fig. 1. Consolidation cell

sure (Druck PDCR-lOF, 100 kPa range for direct measurement and Druck PDCR-120, 100 kPa range for differential measurement). The differential pressure transducer enabled the difference in pore water pressure across the sample to be measured when drainage was allowed to a back pressure. In these experiments, with no back pressure, the differential pressure transducer simply acted as a back-up, and confirmed the results of the base pore water pressure transducer. Both transducers were mounted outside the cell, connected through the drainage line in the base pedestal to the pore water in the sample. The horizontal total stress at the mid-plane of the sample (125 mm above the base) is measured by a miniature flush diaphragm strain-gauge-type pressure transducer (Druck PDCR-200, 100 kPa range). The diameter of this transducer diaphragm was 3 mm. The transducer was fitted into the cell wall with its diaphragm made flush with the cylindrical wall by a drop of self-levelling silicon rubber sealant (Silastic 734RTV). The sealant lens was less than 0.5 mm thick. It remained elastic even after drying, and effectively transmitted lateral total stress from the soil to the transducer. Under a stress of 100 kPa, the transducer diaphragm deflects about 5 urn, according to the manufac- turer. A pressure transducer (Druck PDCR-lOF, 100 kPa range), with a small sintered stainless steel filter plug mounted in front of it, detachable for cleaning and saturating, is installed into the consolidation cell at the same height as the lateral total stress transducer to measure pore-water pressure. These two measurements enabled the lateral effective stress to be determined.

The pressure transducers are calibrated simul-

taneously inside the consolidation cell subjected to the same water pressure. The reference pressure for the calibration is taken from a pore- pressure transducer with known transducer constant and good linearity. Calibrations are carried out at the beginning of each test. Water pressure tests conducted at the end of some of the tests indicated that a small amount of zero drift had occurred giving an overall accuracy of stress measurement better than f0.5 kPa. The conse- quent accuracy of K, measurement is better than _+ 0.02.

Control system The apparatus consists of a microcomputer, the

autonomous data acquisition unit (ADU-ELE, 1984), the loading control system and the consolidation cell. The computer acts as a communica- tor with the ADU which records data, controls the loading system and maintains the room tem- perature at 20C f 1C.

The loading system consists of an air pressure actuator connected to an air-oil interface and a hydraulic jack. The resolution of the air actuator is 0.025% of the full-scale range of 840 kPa (i.e. kO.21 kPa); the area ratio of the hydraulic jack to the sample is 0.66 to 1. This gives an overall loading resolution of kO.14 kPa on the soil sample, which was adequate to maintain the lowest controlled gradient used in the tests. The loading system is closed-looped with the ADU, which is programmed to maintain the required pore-water pressure gradient during the test. The time interval for each looping and regulation was set to 5 s.


Sample preparation Kaolin was chosen as the soil for these tests

because of the large amount of reported research on it, its homogeneity when purchased com- mercially, its convenience of preparation and its generally low creep. The kaolin used in the experimental work is a white powder marketed as Speswhite China clay, which is excavated in Cornwall. Two methods of sample preparation were adopted : remoulded and sedimented. Samples were prepared with distilled water or sea water; the latter was prepared by mixing good- quality sea salt (Tropical Marine) with distilled water. The liquid limit and plastic limit are 58% and 30% respectively in distilled water and 62% and 36% with sea-water chemistry.

The remoulded samples were prepared by mixing dry kaolin with water at a water content of 175%, more than twice the liquid limit. This was wet enough to allow thorough mixing without entrainment of air into the soil. Sedi- mented samples were prepared by mixing 1.5 kg of dry kaolin to form a dilute slurry of initial density 1.055 g/cm. The slurry was then pumped into a 2 m high sedimentation column at whose base the consolidation cell was mounted. Sedi- mentation was carried out for a period of 3 days before the careful removal of the consolidation cell with the sample for the subsequent controlled gradient consolidation stage. The void ratios at the end of sedimentation for distilled and sea- water samples were about 4.3 and 3.5 respectively.

RESULTS There were four different sets of test conditions,

depending on the specific combination of sample

Table 2. Test summary

preparation technique (remoulded or sedimented) and water chemistry (sea or distilled water). Tests were carried out at one of three hydraulic gra- dients, i = 5, 10 or 50; some tests were repeated. Table 2 summarizes the test conditions. For clarity the results now given are for eight tests only: the repeated ones are omitted. However, the repeated tests are subsequently compared directly with each other.

Typical results of stresses and displacement Figure 2 shows typical observations from one

of the slower tests, i = 5, loaded to a vertical stress of 150 kPa over 64 h. Both pressure transducers recording the pore pressure at the base of the cell gave the same readings, marked simply as differential pore pressure (Fig. 2). The pore water pressures are evidently very small. The vertical effective stress can therefore be assumed with con- fidence to be reasonably uniform across the sample. The results of the faster test (i = 50) are not shown, but are similar in form, although larger differential pore pressures were generated up to a maximum of 25 kPa at the beginning of the consolidation stage, reducing to about 13 kPa when the soil sample was later consolidated to a final thickness of about 27 mm.

Stress-strain curves The consolidation curves e-log crV for the dis-

tilled water remoulded (KRD) and sedimented (KSD) kaolin samples (Fig. 3) are almost identical, suggesting that the two fabrics are essentially similar and no particle segregation has occurred through sedimentation. Also, there is no apparent difference between the results of sea-water (KRS)

Test Sample Fluid Hydraulic Final void ratio preparation chemistry gradient (at 150 kPa) technique

KRS-CG-6 Remoulded Sea water 5 1.34 KRS-CG-7 Remoulded Sea water 50 1.29 KRS-CG-8* Remoulded Sea water 50 1.27

KRD-CG-10 Remoulded Distilled water 50 1.32 KRD-CG-9* Remoulded Distilled water 10 1.32 KRD-CG-11 Remoulded Distilled water 10 1.31

KSS-CG-2 Sedimented Sea water 5 1.14 KSS-CG-14* Sedimented Sea water 5 1.16 KSS-CG-8 Sedimented Sea water 50 1.16

KSD-CG-6 Sedimented Distilled water 10 1.33 KSD-CG-5 Sedimented Distilled water 50 1.32 KSD-CG-1 I* Sedimented Distilled water 50 1.33

* Repeated test.

DEVELOPMENT OF K, IN SOFT SOILS 105

Top vertical tots. stress

Base veriical total stress

Horizontal total stress

60 40

0 L 0

Percentage settlement

Dlfferentlal pore pressure

Time: h

Fig. 2. Typical results from controlled gradient consolidation tests: teat KS-CG-2, HO = 4922 mm, i = 5-O

and distilled water remoulded (KRD) samples. This is in accordance with the observations of Sides & Barden (1971), who reported difficulty in flocculating large colloidally inert kaolinite.

However, salt did affect flocculation during sedimentation. For the entire range of effective stress, Fig. 3 shows a considerable difference between the e-log eV results of sea water (KSS) and distilled water (KSD) sedimented samples. The sedimented sea-water samples have consistently lower compression index C,, and lower void ratio. The consistency of the test results for the same water chemistry indicates good repeata- bility of the tests.

2.6-

2.4 -

K, results Figure 4 shows the values of K, plotted against

vertical effective stress, demonstrating that K, is not independent of the vertical effective stress as is usually assumed. The value of K, increases non-linearly with vertical effective stress, with a low K, value during the early formation of soil mass from slurry. The higher the rate of K, increase, the lower is the stress level; this increase mainly occurs below an effective stress level of 30 kPa. The rate of increase reduces at higher stress levels, although results of tests KSD-CG-11 and KSS-CG-14 show that there is a trend for K, to continue to increase up to consolidation stresses

Test

x - KRS-CG-6 0 __ KRS-CG-7

+ - KRD-CG-10 XI 0 q ~ KRD-CG-11

x Q.+

. __ KSS-CG-2

fi - KSS-CG-6

zx . __ KSD-CG-6

5% . __ KSD-CG-5

. fi .

.

0.6 I1l111, I I 1 IC111, r

1 10 100 a,: kPa

Fig. 3. e-log a, from controlled gradient consolidation tests


r r Range of K, correlations

*:+- +- . x KRS-CG-6

0 KRS-CG-7

0 + KRD-CG-10

0 KRD-CG-11

. KSS-CG-2

n KSS-CG-6

v KSD-CG-6

l KSD-CG-5

0 I I I I I I I I, I

50 100 150 uv: kPa

Fig. 4. Ko-u, from controlled gradient consolidation tests

of 300 kPa. A similar pattern is apparent if K, is due in some way to different fabric arrangements plotted against the horizontal effective stress. in the two situations.

A consistently linear K,-e relation was observed in each test (Fig. 5). There is a wide spread of results, but it seems to be a consistent pattern that the lower values of K, at a given void ratio are associated with the two sets of sedimented samples. The difference between sea-water and distilled water sedimented samples observed in the e-log gu plots does not exist in the present correlation. The overall range of the results is higher than would be expected from natural variability between tests, as demonstrated in Fig. 6, which shows repeated tests under identical conditions, two remoulded and two sedimented, with little variation between pairs of tests. It therefore seems likely that the difference between remoulded and sedimented samples is real, and

The best-fit least-square straight lines for the K,-e variations in Fig. 5 have the equations

K, = -0.22e + 0.90

correlation coefficient - 0.90 (1)

K, = -0.25e + 0.87

correlation coefficient -0.95 (2)

for remoulded and sedimented kaolin respectively. If a realistic estimate of the lowest likely values of void ratio e is taken, and it is assumed that these equations will hold for the full range of void ratios, they indicate that upper bounds on K, of about 0.8 and 0.75 may exist for remoulded and sedimented samples respectively. It must be

0.6

Ko = -0.22e + 0.90>. 6

u 0.4 -F I

HTa .

Ko = -0.25e + 0.67

Test

x KRS-CG-6

0 KRS-CG-7

+ KRD-CG-10

0 KRD-CG-11

l KSS-CG-2

A KSS-CG-6

. KSD-CG-6

l KSD-CG-5

I I I I I I I I I I I I I 2-4 2.2 2.0 l-6 1.6 1.4 1.2 1-O

e

Fig. 5. K,-e from controlled gradient consolidation tests

DEVELOPMENT OF K, IN SOFT SOILS 107

r 150 < uv < 300 kPa

0.6 -

+f* *++ i-

u x+ +* 7

X.X :X=xX&

x x 0.4 - + l x x

l X +

+ KRD-CG-10 l l X X l KSD-CG-5 X KRD-CG-9 x x x KSD-CG-11

o-2 A I I I I I I I I I I

2.2 2.0 1.6 1.6 1.4 1.2

0.6 -

160 < 0 < 300 kPa

I-

0 O

oy Q @@@oxoo( x xx$*Xxx

XX...

u 0 xx Xm

0.4 - m m

0 KRS-CG-7 m KSS-CG-2

X KRS-CG-6 X KSS-CG-14

0.2 1 I I I I I I I I 2.2 2.0 1.6 1.6 1.4 1.2 2.0 1.8 1.6 1.4 1.2 1.0 e e

Fig. 6. K,-e variation in repeat tests with identical conditions

emphasized that equations (1) and (2) are the results of the tests carried out in this research for the specified stress range 5-150 kPa. Their appli- cability to lower (say ~5 kPa) or higher stresses (> 150 kPa) must be investigated further.

DISCUSSION Measurement offriction angle q5

To correlate K, with the friction angle 4 for the present test results, consolidated undrained triaxial tests were carried out on remoulded kaolin mixed with distilled water. The triaxial test samples were prepared by consolidating dilute slurry of 175% initial water content in a consolidometer to 100 kPa vertical stress one- dimensionally. The consolidometer is a 100 mm dia. by 300 mm tall cylinder with simple hanger type dead-loading mechanism. The slurry was loaded in 24 h stages to 6.3 kPa (hanger weight) and 25 kPa and then maintained at 100 kPa for 3 days. The consolidated sample had a final thickness of about 100 mm, which provided three 38 mm dia. by 76 mm high triaxial samples. Each sample was further consolidated for 24 h in the triaxial cell under isotropic conditions, with the provision of filter paper side drains, with back pressure 100 kPa and cell pressures 300 kPa, 500 kPa or 700 kPa. (Side drains are not recommend- ed for conditions of one-dimensional consolidation under a uniaxial applied load, due to the non-homogeneities that arise in the consolidated sample. However, given the different boundary

conditions for a sample consolidating under all- round pressure in a triaxial cell, these problems are much less serious.) The samples were sheared in the undrained condition with an axial deformation rate of 0.048 mm/min. Failure was defined by maximum stress ratio. A 4 value of 22 was measured from both stress paths and Mohr circles (Figs 7 and 8). These tests were carried out at higher effective stress levels than the consolidation tests, lower values being very difficult to achieve due to the difficulties of handling very soft samples.

Comparison with K, correlations If an elastic-plastic model is assumed to

describe soil behaviour, the process of normal

400

m 300

4

b- 200 I

. . . -iy;b, ~: , f ~

200 400 600 P = (~1 + 2os)/3: kPa

Fig. 7. Stress paths for undrained triaxial tests on kaolin

108 TING. SILLS AND WIJEYESEKERA

400-

I 0 100 200 300 400 500 600 700

0,'. 03'. kPa

Fig. 8. Mohr circles for undrained triaxial tests on kaolin

consolidation can be identified with the condition of yielding, and expansion of the yield envelope. It is therefore not surprising to find some correlation between K,, a stress parameter of one- dimensional normal consolidation, and the friction angle $, representing the failure condition. Such a correlation is implicit in the empirical determinations of K, given in Table 1. Assuming the value 4 = 22 found from the triaxial tests for effective stress ranges of 200-600 kPa, the calculated values for remoulded kaolin are shown in Table 1. The range is 0.5660.63. By comparison, the K, values measured in the consolidometer for remoulded kaolin mixed with distilled water lie within this range for effective stresses above 70 kPa, and are therefore consistent with the original correlations. Below about 60 kPa, however, the K, values are lower than the empirical correlation would suggest if the value of 4 were constant independently of stress range. However, if 4 is assumed to be higher at low effective stresses, the correlation may still be valid. It is difficult to measure 4 at these stress levels in the triaxial test, but Kamhawi (1992) reported experiments in direct shear under conditions of controlled shear load increment on kaolin consolidated from slurries of initial water content about 400%. They found a failure angle of 22.5 at vertical stresses > 10 kPa, with 38 for ~5 kPa vertical stress. In displacement- controlled tests, on the other hand, they found values of 22.5 at all stress levels. The high values of 4 were attributed to thixotropy, developed in the time elapsed between the shear load increments, and therefore not occurring in the displacement-controlled tests. If a value of 4 = 38 is taken, the corresponding value of K, calculated from (1 - sin 4) is 0.38. The consolidometer results for kaolin (both sedimented and remoulded) shown in Fig. 4 lie between 0.33 and 0.44 for a vertical effective stress of 10 kPa. Thus, although the conditions of the controlled gradient test would not traditionally be expected to cause

thixotropic effects to develop, it is clear that 4 values can be sufhciently high at low stresses to explain the observed K, values within the pre- viously proposed empirical correlation.

CONCLUSIONS Experimental observations indicate that K, is

not a constant parameter, but increases non- linearly with increasing effective stress, the lowest values and the fastest changes of K, occurring at low stress levels. The fact that the K, correlation has been observed to vary linearly with void ratio offers an intriguing possibility of predicting qS values at lower effective stresses from the void ratio+.ffective stress relation for the soil. Thus, by measurement of K, at higher stress levels (say, within an effective stress range of 100-500 kPa), the appropriate K,-e relation could be estab- lished. This could then be extrapolated to higher void ratios, corresponding to softer soils. The value of 4 could be calculated from K, = 1 - sin 4: and related to the corresponding effective stress level by way of the effective stress-void ratio relation. The present data would support this approach down to effective stress levels of about 10 kPa.

Extrapolation of the linear K,-e correlation in the other direction, assuming a likely minimum value of e, allows an upper bound to be placed on K, and hence on 4. However, there is less justifi- cation for this from the experiments reported here, since none have been carried out to confirm that the linear relation holds at effective stress levels above 500 kPa. Comparison of sea-water remoulded and sedimented kaolin sample results indicates a large effect of fabric on compressibility, with a much smaller effect on K,

The results of this experimental programme confirm that soft soils cannot, in general, be treated simply by applying parameters obtained at higher stress levels. However, they also suggest that the general relations still apply, provided that appropriate parameters are used.

NOTATION e

cc HO

4 M

OCR P 4

01) u3

0

void ratio compression index initial height hydraulic gradient coefficient of lateral earth pressure at rest critical stress ratio overconsolidation ratio mean effective stress deviatoric stress principal effective stresses vertical effective stress shear stress effective angle of shearing resistance

K, IN SOFT SOILS 109

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earth pressure of a consolidating clay. .I. Geotech. Engng Div. Am. Sot. Civ. Engrs 102, GT7,721-738.

ADU-ELE (1984). Autonomous data acquisition unit-a new approach to data acquisition. Equipment hand- book. Engineering Laboratory Equipment Interna- tional.

Bishop, A. W. (1958). Test requirements for measuring the coefficient of earth pressure at rest. Proceedings of conference on earth pressure problems, Brussels 1, 2-14.

Brooker, E. W. & Ireland, H. 0. (1965). Earth pressure at rest related to stress history. Can. Geotech. J. 2, 1-15.

Davis, E. H. & Poulos, H. G. (1963). Triaxial testing and three-dimensional settlement analysis. Proc. 4th Aus.-NZ ConjI Soil Mech., Adelaide, 233-243.

Edit, T. B. & Dhowian, A. W. (1981). At rest lateral pressure of peat soils. J. Geotech. Engng Div. Am. Sot. Civ. Engrs 107, GT2,201-217.

Fraser, A. M. (1957). The influence of stress ratio on compressibility and pore pressure coefficient in com- pacted soils. PhD thesis, University of London.

Jaky, J. (1944). The coefficient of earth pressure at rest. J. Sot. Hung. Archit. Engrs 78, 355-358.

Jaky, J. (1948). Pressures in silos. Proc. 2nd Int. Conf. Soil Mech., Rotterdam 1, 103-107.

Kamhawi, K. Z. R. (1992). The shear strength of two

resedimented clays at low and very low effective stresses. PhD thesis, University of London.

Lewin, P. I. (1970). Stress deformation characteristic of saturated soil. MSc thesis, University of London.

Lowe, J., Jonas, E. & Obrician, V. (1969). Controlled gradient consolidation test. J. Soil Mech. Fdn Engng Div. Am. Sot. Civ. Engrs 95, SMl, 77-97.

Menzies, B. K. Sutton, H. & Davies, R. E. (1977). A new system for automatically simulating K, consolidation and K, swelling in the conventional triaxial cell. GCotechnique 27, 593-596.

Moore, C. A. (1971). Effect of mica on K, compressibility of two soils. J. Soil Mech. Fdn Engng Div. Am. Sot. Civ. Engrs 97, SM3, 1275-1292.

Newlin, C. W. (1965). Lateral stresses during one- dimensional consolidation. PhD thesis, Northwestern University, Evanston.

Rowe, P. W. (1957). C, = 0 hypothesis for normally loaded clays at equilibrium. Proc. 4th Int. Conf: Soil Mech., London, 1899192.

Schmidt, B. (1967). Discussion on Earth pressure, by E. W. Brooker et al. Can. Geotech. 3. 3,239-242.

Sides, G. & Barden, L. (1971). The microstructure of dispersed and flocculated samples of kaolinite, illite and montmorillonite. Can. Geotech. J. 8, 391-399.

Singh, R., Henkel, D. J. & Sangrey, D. A. (1973). Shear and K, swelling of overconsolidated clay. Proc. 8th Int. Conf: Soil Mech., Moscow 1, 367-376.

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Ge 440106