Cyclic Critical Stress States of Sand with Nonfrictional Effects

Abstract

New observations of experimental facts are made in this study to understand the physical essentials regarding the changes in mobilized maximum stress and phase-transformation stress states of saturated sands subjected to cyclic undrained shear applications. Saturated sands are not purely frictional materials that are governed only by frictional law (i.e., the shear-normal stress ratio). They are also characterized by the following effects of nonfrictional behavior: (1) Irreversible dilatancy effect; (2) viscous effect at large strain rate; and (3) coupling effect of viscous to frictional resistance. It was found that the first effect reduces the limiting shear resistance, whereas the second and third effects increase it. Based on this finding, 2D and 3D criteria that consider both the frictional and nonfrictional effects are developed by introducing several new concepts such as the “true effective stress,” “moving stress space,” and “moving spatially mobilized plane.” Their effectiveness is confirmed experimentally.