LIQUEFACTION OF SAND UNDER BIDIRECTIONAL MONOTONIC AND CYCLIC LOADING

A laboratory study is presented of the liquefaction behavior of sand subjected to bidirectional monotonic and cyclic simple shear loading conditions using a new bidirectional simple shear apparatus. Tests were performed with the monotonic and cyclic components being ''parallel'' and ''perpendicular'' to provide an approximate representation of the seismic loading conditions produced within earth embankments or slopes by the transverse and longitudinal components of motion, respectively. For a static horizontal shear stress ratio of 0.2 to 0.3, for a sand at relative densities of 35%, 45%, and 55%, and for failure criteria of 3% to 7.5% single amplitude shear strain, the perpendicular (i.e., longitudinal) cyclic loading resistance ranged from 70% to 95% of the parallel (i.e., transverse) cyclic loading resistance. The lower cyclic loading resistance for perpendicular versus parallel static and cyclic loads is attributed to differences in the amount of principal stress rotation and shear stress reversal that occurs for these two loading conditions.