UNDRAINED DEFORMATION CHARACTERISTICS OF SAND IN MULTI-DIRECTIONAL SHEAR

Abstract

In order to study the deformation and liquefaction characteristics of sand subjected to cyclic stresses involving changes not only in magnitude but also in direction, several series of static cyclic tests were performed on cubical saturated sand specimens in undrained conditions using a true triaxial test apparatus. The octahedral plane in the three-dimensional stress space was envisaged as representing the horizontal plane in the in-situ sand deposit, and three principal stresses were cyclically applied to the specimens so that circular, elliptic and crisscrossing stress paths could be produced in the octahedral stress plane. The analysis of stress and strain increment vectors on the octahedral plane showed that the sand manifests the deformation characteristics like an elastic body at the beginning of cyclic loading where the developed pore water pressure is still small, but at the end of the cyclic loading near the incidence of liquefaction the sand tends to behave more like a perfectly-plastic body. The results of the tests also indicated that the resistance to liquefaction became smaller as the stress paths changed from the straight-line to the ellipse and further to the circle.