A state-dependent elasto-plastic model for saturated and unsaturated soils

Abstract

A state-dependent elasto-plastic constitutive model for both saturated and unsaturated soils is presented in this paper. The model, which is developed under an extended critical-state framework, uses two independent stress state variables: net normal stress and matric suction. In addition, the influence of a simplified non-linear soil-water characteristic curve on mechanical behaviour is incorporated in the model by using a bi-linear function. Most importantly, a state-dependent dilatancy formulation is introduced to account for the effects of stress level or stress ratio, internal state (density) and soil suction. In this paper, details of the model formulation and the determination of model parameters are described and reported. By using the new model, numerical simulations of triaxial tests have been carried out on both saturated and unsaturated fine-grained (sandy silt) and coarse-grained (gravelly sand) weathered soils. The simulated triaxial tests include undrained shear tests on saturated specimens, constant water content tests and wetting tests under constant deviator stress on unsaturated specimens. The computed results show that the stress–strain and volumetric-shear–strain relationships at both loose and dense and saturated and unsaturated states can be modelled properly with a single set of parameters. Moreover, the model is capable of capturing some key observed features, such as a sudden increase in shear strain and volumetric strain as suction is reduced under a constant deviator stress.

Stability analysis of rainfall-induced slope failure: a review

“…Constitutive models for the hydro-mechanical behaviour of unsaturated soils can be divided into two groups: elastic models (Lloret et al, 1987;Thomas and He, 1997) and elasto-plastic models (Chiu and Ng, 2003;Georgiadis, 2003;Thomas and He, 1998;Toll, 1990;Wheeler and Sivakumar, 1995;Wheeler et al, 2003). Alonso and his colleagues have developed a series of coupled hydro-mechanical models with increasing complexity to deal with problems of the flow in saturated and unsaturated soil systems and the mechanical interaction associated with changes in soil suction (Alonso et al, 2003;Lloret and Alonso, 1980;Olivella et al, 1996).…”

Modelling hydro-mechanical behavior for unsaturated soils

“…Most models in the literature use suction either as a stress (external) variable or as a hardening (internal) variable. Some of these models are established in the space of net stress and suction (e.g., Alonso et al, 1990;Cui and Delage, 1996;Chiu and Ng, 2003;Thu et al, 2007;Sheng et al, 2008a;Zhou and Sheng, 2009), whereas others are in the space of effective stress (Bishop, 1959) and suction (e.g., Kohgo et (2) The yield surface or the elastic zone is defined in the space of stress versus suction; (3) The shear strength is defined in terms of stress and suction (or degree of saturation).…”

Yielding of rockfill in relative humidity-controlled triaxial experiments

“…This formulation was also adopted by Chiu & Ng (2003) in their constitutive model for unsaturated soils recognizing that material parameters should also depend on suction. Cecconi et al (2002) criticize also the oneto-one correspondence between d and  implied in the classic dilatancy models.…”