Abstract

ABSTRACT Based on the results of a series of cyclic triaxial tests and cyclic torsional simple shear tests on saturated Toyoura sand performed under drained conditions, stress-dilatancy equations under cyclic loadings were studied. It has been found from the experimental work that in each of the testing methods a unique relationship between the stress ratio and the rate of dilatancy (strain increment ratio) exists which is independent of void ratio and pressure level. It has also been found experimentally that the rate of dilatancy, as defined as the rate of volumetric strain increment to shear strain increment (positive for volume expansion), becomes negative by unloading after the reversing of loading direction, and it increases continuously with shearing without showing any discontinuous behavior at the moment when the sign of shear stress changes, and subsequently it becomes positive. Thus, at the same stress condition, two different rates of dilatancy are possible to exist depending on the direction of shear straining. Four different representative stress-dilatancy relations based on (i) the sliding block theory, (ii) the Rowe’s theory, (iii) the Roscoe’s energy dissipation theory, and (iv) the Taylor’s energy dissipation theory, were modified to apply to cyclic loading conditions with reversed loading directions. It was found that after these modifications some of these theories can well simulate the stress-dilatancy relations under drained cyclic conditions obtained by the tests. Finally, curves of equal plastic potential in cyclic drained simple shear were portraied on a stress plane. It is a double plastic potential function in the sense that two different plastic potential curves are passing through any given stress point, which are for two different directions of shear-straining.

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