A three-phase model for unsaturated soils

Abstract

SUMMARYA comprehensive framework to de"ne the constitutive behaviour of unsaturated soils is developed within the theory of mixtures applied to three-phase porous media. Each of the three phases is endowed with its own strain and stress. Elastic and elastic}plastic constitutive equations are developed. Particular emphasis is laid on the interactions between the phases both in the elastic and plastic regimes. Nevertheless, the clear structure of the constitutive equations requires a minimal number of material parameters. Their identi"cation is provided: in particular, it incorporates directly the soil}water characteristic curve. Crucial to the formulation is an appropriate de"nition of the e!ective stress. The coupled in#uence of this e!ective stress and of suction makes it possible to describe qualitatively many of the characteristic features observed in experiments, e.g. for normally consolidated soils, a plastic behaviour up to air entry followed by an elastic behaviour at increasing suctions, and, on the way back, an elastic behaviour, unless compression is applied in which case plastic collapse occurs.

Strain Localization in Unsaturated Elastic-Plastic Materials Subjected to Plane Strain Compression

“…The relationship between the effective stress and strain equivalent to the one given by Loret and Khalili (2000) …”

“…Rates of change of pore water and pore air volumes per unit reference volume under the assumptions adopted herein, were given by Loret and Khalili (2000) …”

Experimental Study on the Behavior of Unsaturated Compacted Silt Under Triaxial Compression

“…Stress variables for suction and the excess total stress over the air pressure (or the excess total stress over the water pressure) have been used to describe the mechanical behavior of unsaturated soil (Bishop, 1960;Fredlund and Morgenstern, 1977;Alonso et al, 1990;Wheeler and Sivakumar, 1995). Karube and Kawai (2001) used a generalized Bishop's stress, while Kohgo et al (1993) and Loret and Khalili (2000) adopted an eŠective stress that includes constitutive parameters. Recently, the term``eŠective stress,'' or``average skeleton stress,'' has been used when considering the mixture theory (Bolzon et al, 1996;Jommi, 2000;Ehlers et al, 2004).…”

Cam-Clay plasticity. Part V: A mathematical framework for three-phase deformation and strain localization analyses of partially saturated porous media

“…Energy consideration provides support for this idea, at least from a continuum standpoint, as well as elucidates possible definitions for a constitutive effective stress conjugate to the macroscopic deformation of the solid matrix. Possible constitutive effective stresses include the net stress and the Bishop stress [5][6][7][8][9][10][11][12][13][14][15].…”