A Unique Critical State for Sand?

Abstract

The development of localized strains (shear banding) in soils near peak stress levels and the subsequent continued deformation within shear bands during observed softening render important issues such as critical state difficult to investigate. The determination and overall validity of critical state behavior in sand is of considerable importance, as it provides the basis both for failure criteria/postfailure behavior of many constitutive models and for stability analysis. A series of drained plane-strain experiments on sand specimens with detailed local analysis was carried out to investigate the evolution of stress state and void ratio, as well as the uniqueness of critical state. Persistent shear bands form at the peak effective stress ratio; subsequent strain softening behavior occurs in concert with localized deformation with the shear band. A unique critical stress state was found to exist for a given confining stress; however, the test results indicate that there is no unique relationship between void ratio and confining stress at the critical state.