A UNIQUE CRITICAL-STATE FOR SAND

The development of localized strains (shear banding) in soils near pea k stress levels and the subsequent continued deformation within shear bands during observed softening render important issues such as critic al state difficult to investigate. The determination and overall valid ity of critical state behavior in sand is of considerable importance, as it provides the basis both for failure criteria/postfailure behavio r 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. Persiste nt shear bands form at the peak effective stress ratio; subsequent str ain softening behavior occurs in concert with localized deformation wi th the shear band A unique critical stress state was found to exist fo r a given confining stress; however, the test results indicate that th ere is no unique relationship between void ratio and confining stress at the critical state.