ABSTRACT
ABSTRACT: The paper presents a generalized plasticity stress-strain relation for unsaturated soils. The constitutive equations are introduced by thermodynamics; the decomposition of the Helmholtz free energy is used to explain collapse strain recorded upon wetting. The model is formulated by a thermodynamically consistent expression of the effective stress acting on the solid skeleton. Besides, the hierarchical enhancement of the basic saturatedmodel is obtained introducing a second plastic term. The mechanical equation is coupled with a scalar function defining the water storage mechanism which is modelled accounting for its hydraulic hysteresis. The basic saturated generalized plasticity model is recovered in the presented formulation, as special case, when the saturation degree is equal to one and the transition between saturated and unsaturated conditions takes place without discontinuity. The model can reproduce the behaviour of unsaturated soils under monotonic stress path and it is also suitable for cyclic loading. Numerical validations of the proposed equations are reported.
