A hypothetical rheological model of the nonlinear Maxell type has been proposed to study the stress-strain characteristics of a saturated clay, assuming the soil structure resistance to be viscoelastic. The various elements in the proposed model consider both the elastic and viscous character of clays. The viscous character is considered in the form of structural viscosity derived from the considerations of the theory of rate processes. Experimental verification is done by strength tests on saturated kaolinitic clay whose initial structural state is mainly controlled by system chemistry. The existence of postulated initial structural difference has been amply substantiated by indirect and direct methods of identification of soil structure. An attempt has been made to explain the relationship between the flow parameters and the mechanism of the clay behaviour in relation to initial soil structure. The experimental evidence regarding the prediction of the model has been examined and the limitations highlighted. It is believed that this analysis would ultimately help in developing a more comprehensive constitutive relationship.Prediction of the general stress-strain behaviour of clays has been the object of numerous investigators in recent times. A general picture of this behaviour would be of immense help not only in understanding the stress-strain relations but also in forming a basis of solving many field problems with given stress or strain paths. It is postulated that the shearing stresses developed in a saturated clay subjected to a constant rate of strain are due to the resistance offered by the forces developed at interparticle contacts. Further deformation of a soil mass involves microscale movements of particles and proceeds at a rate commensurate with the initial structural state of clay-water-electrolyte system and the rate of strain (Mitchell 1964). The theory of rate processes is being used in the analysis of stress-strain-time behaviour of saturated clay since it postulates that an activation energy is required for loosening of particles from their equilibrium positions and displacement to new positions. Much of the pioneering work on the deformation behaviour of clays is done by Murayama and Shibata (Murayama and Shibata 1958, 1959, 1961) by applying the theory of rate processes. Analysis of shearing resistance (Mitchell 1964) and consolidation behaviour (Wu; Resendiz and Neukirchner 1966) have also been attempted by the application of theory of rate processes.

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Idealizations in soil mechanics are usually necessary in order to obtain solutions and to have these solutions in a readily applicable form. Limit equilibrium has been a method of solving various soil stability problems.One weakness of the limit equilibrium method has been the neglect of the stress-strain relationship of the soil. According to the mechanics of solids, this condition must be satisfied for a complete solution. Limit analysis, through the concept of a yield criterion and its associated flow rule, considers the stress-strain relationship. However, a soil with cohesion and internal friction is not modeled accurately by a theory of perfect plasticity. Nevertheless, indications are that the stability problems in soil mechanics will, in time, be computed on the basis of the limit theorems of plasticity. A discussion is given, therefore, of the significance of the limit analysis in terms of the real behavior of soils and their idealizations. With this background the meaning of existing limit equilibrium solutions is discussed, and the power and simplicity of application of the limit analysis method is demonstrated.

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When an accurate stress analysis is to be made for excavation problems, it is desirable to make a step-by-step calculation by simulating the actual steps of excavation procedure. In this connection, there arise some fundamental questions as to whether the solutions are all identical when the order of cutting is changed, and whether the solution for multistage cutting equals that for a single-step cutting. To check the uniqueness of the solution for these different methods of cutting, the uniqueness proof was investigated by following the conventional method of approach which has been used extensively in the theory of elasticity and plasticity. The well-known theorem of virtual work was applied to the proof together with the stress-strain relationship of the material. It is shown that the uniqueness depends strongly upon the material properties, and that the sufficient condition for the uniqueness to be established is that the material is linear, time-independent and elastic throughout the cutting process.

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Response of vertical pile to the action of lateral loads is one of the complex soil-structure interaction problems in the field of foundation engineering. Any realistic analysis of the problem should take into account both the elastic and plastic properties of the soil, as both these states occur along the embedded length of the pile. Herein, analysis of laterally loaded piles is presented taking elasto-plastic nature of the soil into account for both cohesive and cohesionless soils. The results show that the flexural behaviour of laterally loaded pile in an elasto-plastic soil is considerably influenced by type of variation of plastic resistance, soil modulus variation and the boundary conditions at the top.

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In the application of the Fellenius, the Bishop and the friction circle methods of slope stability analysis the factor of safety is defined in terms of the failure shear stress that may be mobilized at the existing in-situ value of effective normal stress. No account is taken of the additional pore pressure change (positive or negative) that may occur between the in-situ state and the failure state when the possibility of undrained failure is being examined. Expressions for all three methods in which allowance is made for the development of these additional pore pressures, have been derived. It is claimed that the resulting redefinition of the factor of safety is more logical and more valid than the conventional definition. The use of these expressions is illustrated by their application to the analysis of the failure of the Seven Sisters embankment in Canada.

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The finite element method of analysis has been applied to a wide variety of problems in the realm of soil and rock mechanics during the past few years. This information is published in a number of technical journals in various disciplines, and the paper reviews the developments that are of particular interest to soil engineers. Applications of the method to problems in slope stability, embankments, culverts, pavements, bearing capacity, piles, soil dynamics, seepage and rock mechanics are reviewed. General comments on the state of the art of the subject are made.

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