Three-Dimensional Constitutive Model for Partially and Fully Saturated Soils

Abstract

Constitutive models for partially saturated soils often assume linear relationships for the variation of shear strength with suction and the shape of the partially saturated isotropic compression lines. It has been established, however, that for some soils these relationships are nonlinear. The shape of the isotropic compression line for partially saturated conditions is of particular importance, as it is directly related to the amount of potential collapse that a soil will experience upon wetting. When boundary value problems are analyzed, ignoring this nonlinearity can lead to very inaccurate predictions, and such models are of limited applicability. None of the current models have been demonstrated to predict collapse behavior in a satisfactory manner, especially at high values of stress and suction. In this paper, an exponential expression for partially saturated isotropic compression lines is implemented in an existing elastoplastic framework for saturated and partially saturated soils. As a result, the constitutive relationship presented here is more flexible in its ability to model the collapse behavior of partially saturated soils over a larger range of suctions and stresses. A nonlinear expression is also adopted for the variation of shear strength with suction. In addition, a number of other refinements to the existing framework are introduced. Also presented in this paper are the results of a series of single element finite-element analyses. These results demonstrate the model’s capabilities and added flexibility.