ABSTRACT
These last few decades some new models accounting for unsaturated soils behavior were developed using enlarged effective stress concept (Russel and Kalili, 2006, Pereira et al. 2005, Coussy et Dangla 2002, Laloui et al. 2009, Loret and Khalili 2002). These models are, in most of cases, adaptation of existing models that were initially developed for saturated or dry soils as CJS (Cambou, 1988) for Pereira (2005). This article presents some calculations about the incorporation of suction in models adapted for unsaturated soils. For those models where effective stress and suction are used as independent state variables, suction plays a double role. It represents firstly a loading parameter since suction physically induces a mutual attraction between grains and is in a way similar to an external compressive loading. On the other hand, however, it also induces a strengthening effect because this attraction force increases the
normal contact pressure between grains hence the shear strength against inter-granular sliding. Relative to theoretical modeling using plasticity theories, this phenomenon of capillary hardening can be simulated by an expansion of the elastic domain bounded by the yield surface. This double role played by suction is reflected in the fact that suction intervenes twice in the plastic yield function: on one hand it defines the effective stress and on the other hand it also represents the shear strength as an independent variable in the yield function. It can be taken into account in theoretical modeling as a generalized stress variable or not. So we will consider as “case 1” the case where suction is considered as a generalized stress variable. And we named “case 2” the other case (Table 1).
