Results of drained and undrained triaxial compressions tests on a sensitive clay are presented in this thesis. Contours of water content from both drained and undrained tests are compared, and it appears that for the clay tested, there is not a unique relationship between effective stresses and water content as found by Rendulic and Henkel for remolded soil. The Roscoe concept of a state boundary surface, which is similar to the Rendulic concept is examined, and it also does not hold for the clay tested. The Roscoe energy equation is applied to the results of all tests and it appears to hold quite well. It indicates that for a soil which is yielding there is only one fundamental strength parameter, M, which is independent of both strain and strain rate. Methods of predicting stress-strain relationships are examined. The Roscoe method, which is based on the existence of a state boundary surface is not strictly applicable, but does yield results which are of the same order as the measured relationships. The Landanyi method does not appear to apply to the clay tested. A method for predicting residual pore pressures and or permeability in drained triaxial tests is derived. This enabled allowances to be made for the effect of residual pore pressures in drained tests. However, it is felt that the method may have more application in the examination of soil structure, since a comparison of the permeability of samples at the same void ratio and temperature yields a measure of structural difference. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

A review is given on the factors important to the build-up of a gel structure in clay suspensions. The effect of salt is especially stressed. The maximum yield stress of a 19.06 weight per cent washed Bentonite clay paste was measured with a Rotovisco viscometer as a function of the concentration of five salts which were added individually to the paste. The salt concentration was varied from .002 molality up to the coagulation concentration. Two groups of salts were studied; those which had cations in common with the caly: NaCl and CaCl₂, and those found only in trace amounts in clay: CuCl, MnCl₂ and CeCl₃. The behavior of the two groups of salt was quite different. The latter group produced a maximum developable yield value in the clay which was inversely proportional to the valence of the cation. Sodium Chloride produced the largest maximum yield value at a high salt concentration while no yield value could be found for clay with concentrations of CaCl₂ above 0.002M. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

A theoretical and experimental investigation into the creep of a sensitive clay under different deviator stresses is presented. The effect of deviator stress on pore-pressures within the soil is also studied. An explanation of the phenomenon of creep is offered which is based on a consideration of the micro-structure of the clay. Experimental evidence to support this explanation is presented. The experimental work consisted of standard triaxial "consolidated undrained tests" performed on cylindrical specimens. Pore-pressures were measured by means of a pore-pressure panel based on the M.I.T. design. The observed data show that, with other variables remaining constant, the strain rate increases with increase in applied stress. Experimental results do not conclusively prove the existence of an upper yield value for the clay tested, but they do suggest it as a possibility. With the temperature remaining constant, the test results show that the pore-pressure increases with increase in applied stress. Under a given applied deviator stress the pore-pressure increases at a decreasing rate and does not attain a maximum or constant value at any time during the test. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

An important consideration in the design of clay foundation for seismic or wave loading is the undrained response of clay during and after cyclic loading . Cyclic loading of clays causes, in general, a reduction in both stiffness and undrained strength on subsequent static loading. No systematic study has been carried out to assess this loss in stiffness, and there are conflicting conclusions as to the magnitude of strength reduction in studies reported in the literature. This thesis presents a study of the influence of cyclic loading on the post-cyclic undrained stress-strain characteristics of a marine clay. The influence of factors, such as, cyclic stress level, number of cycles, amplitude of maximum axial strain during cyclic loading, residual pore pressure and residual strain at the conclusion of cyclic loading is systematically investigated. In addition, the influence of initiating cyclic loading with the type of loading pulse (compression and extension) and the sense of residual strain in relation to the sense of strain during post-cyclic monotonic loading is studied. It is shown that the loss in undrained stiffness and undrained strength of the undisturbed clay as a consequence of cyclic loading are not uniquely related to the amplitude.of strain during cyclic loading, as commonly assumed. Nor can they be explained in terms of overconsolidation induced as a result of pore pressure generated due to cyclic loading. A rational explanation and correlation of both the changes in post-cyclic stress-strain and strength of clay is provided in terms of hysteretic work absorbed by the clay during cyclic loading. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

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This paper discusses several proposed methods for estimating undrained shear strength from cone penetration tests. This correlation has been studied in the past, however, most have focussed only on the cone bearing. In addition to discussing these traditional methods, this paper evaluates recently proposed methods of estimating Su from CPT pore pressure data. The results of field vane and cone penetration tests from five lower mainland sites are presented in relation to the different proposed correlation techniques. The results show that there is no unique cone factor for estimating Su from CPT for all clays, however, a reasonable estimate of Su can be made by comparing the predictions from several of the proposed methods. With local correlations these techniques can be quite reliable. The results also show that the estimation of Su from CPT is influenced by various factors relating to: the choice of a reference Su, cone design, CPT test procedures and the soil characteristics. In particular, the estimation of Su from CPT is strongly influenced by such soil parameters as stress history, sensitivity and stiffness. Increases in OCR and sensitivity were reflected by increases in the traditional cone factors Nc and Nk. The use of pore pressure data appears to be a promising means of estimating. Su from CPT. Expressions have been developed that predict excess pore pressures based on cavity expansion theory and attempt to include the effects of sensitivity, stress history and stiffness. In addition, comparisons between friction sleeve measurements and Su and a method for estimating sensitivity from friction ratios are presented. Lastly, recommended procedures for estimating Su from CPT are given. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate