A MODELLING PROCEDURE FOR SHEAR YIELDING CHARACTERISTICS AFFECTED BY VISCOUS PROPERTIES OF SAND IN TRIAXIAL COMPRESSION

Abstract

A series of triaxial compression (TC) tests were performed on Toyoura sand to evaluate the viscous effects on the stress-strain behaviour following the shear yielding mechanism. It is shown that very different shear stress and shear strain relations obtained from TC tests performed along different stress paths become rather unique when converted into relationships between the stress parameter X^t_s=(q/p_a)/(p' /p_a)^βf_s, which is deemed to control the shear yield mechanism, and the normalized irreversible shear strain energy k_s, which is the stress path-independent strain hardening parameter for shear yielding. Along each inviscid yield locus quantified based on the test results, with an increase in the effective mean principal stress p', the deviator stress q increases at a relatively large rate while the stress ratio q/p' decreases at a relatively small rate. According to the non-linear three-component model described in the paper, the stress parameter X^t_s is decomposed into the inviscid and viscous components, X^f_s and X^v_s. The inviscid shear yield loci are described in terms of X^f_s and develop with an increase in k_s. The viscosity function g_v(k_s) is introduced to relate X^v_s to X^f_s in the form of X^v_s=X^f_s-g_v(k_s) based on the test results. It is shown that the viscous effects on the X^t_s-k_s relations obtained from the TC tests performed along a wide variety of stress path could be simulated rather well by the model taking into account the decay of the viscous component X^v_s with an increase in k_s.