ABSTRACT
In the last few years an important number of constitutive models based on the single stress variable approach have been developed to simulate the behavior of unsaturated materials. Two of the main advantages in using the single stress approach are that the hydro-mechanical coupling is implicit into the formulation and that a single compressibility index is required, usually written as a function of suction. The simulation of the phenomenon of collapse upon wetting was one of the main objections to this approach in the past. It is presently acknowledge that the simulation of this phenomenon requires, in addition to the effective stress equation, an appropriate elastoplastic framework. This approach can be written in the following general form
d v
dp pv
vε λ= − ′ ′
(2)
where p′ and dp′ represent the preconsolidation effective stress and its increment, respectively and λv represents the slope of the compression curve in the axes of the logarithm of the effective mean stress versus specific volume. Parameter λv can be written as a function of the mean net stress, the
1 INTRODUCTION
Two main trends have been used to study the volumetric behavior of unsaturated soils. One is the independent stress variables approach. The other is the single stress variable approach. In the former two different coefficients are used to account for the contribution of net stress and suction on the volumetric behavior of unsaturated soils. In the later, a single volumetric coefficient is related to a single stress variable (in most cases referred as the effective stress) to simulate the volumetric behavior of these materials.
