Abstract
Elastoplastic models for sand named tij-sand model and kinematic tij-sand model have been proposed which can describe properly the stress-strain behavior of sand under three dimensional stresses. These models can take into account the influence of intermediate principal stress on the deformation and strength of sand by using modified stress tij. However, they can not sufficiently describe the deformation and strength characteristics of sand by using unified soil parameters, when the change in confining pressure and void ratio are involved.
In the present study the previous models are extended to one which can describe not only the influence of the change of void ratio and confining pressure but also strain hardening and softening behavior by introducing a concept named “state variable” based on critical state of sand and Hashiguchi's sub-loading surface concept. The present model is confirmed to be valid by analyzing some triaxial compression and extension tests under drained and undrained conditions on Toyoura sand with different void ratios and different confining pressures. It is shown that the present model can predict well these influences.
