Analysis of Strain Rate Influence on Shear Strength by Rate Processes

Abstract

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.