EFFECT OF FABRIC CHANGE IN MODELING OF GRANULAR MATERIAL RESPONSE UNDER CYCLIC LOADING

Deformation of dams during and after earthquakes is one of the concerns in designing of dams. It was shown that constitutive equation is one of the most important factors in dynamic analysis and design of dams. Modeling of granular material behavior under cyclic loading has not been satisfactory compared with that under monotonic loading. Continuous softening behavior, even in relatively dense sands, is caused by significant decreasing of shear stiffness of granular materials. This continuous softening is made some difficulties in application of advance constitutive models and validity of their parameters in simulating earth and rock-fill dams performance during earthquake. In this study, it was shown that the response of granular materials under cyclic loading can be simulated by using only one set of model parameters, considering the internal fabric of soil and its change during loading. Dilation parameter of a model has been related to a second order fabric tensor. The effect of fabric change during loading and also the effect of previous loading, which were neglected in most of existing constitutive models, were considered partly in this study. As a result, the predictions of the model were modified significantly under cyclic loading.