A Triaxial Characteristic State Model for Sand

A non-associated plasticity model for sand is presented. The loading surface is a closed two-parameter surface in the principal stress space, determined by a size and a shape parameter. The shape parameter is determined explicitly from the slope of the characteristic line. For small mean stress the loading surfaces approach the zero-tension planes asymptotically, generating a nearly triangular contour in the deviator ic stress plane. The gradient of the flow potential is generated directly from the gradient of the loading potential by scaling of the mean stress component. Two hardening rules that permit ultimate stress states beyond the characteristic line have been proposed. Results from drained triaxial tests show good agreement with the model, usi ng a weighted work hardening rule.