NUMERICAL IMPLEMENTATION OF AN ELASTOPLASTIC MODEL FOR UNSATURATED SOILS

This paper describes some issues related to the numerical implementation of a constitutive model for unsaturated soils based on the BBM [1]. The focus of the paper is on the stress variables used and on the numerical algorithms adopted. Conventional stress variable approach (net stress and suction) as well as the approach that takes into account the degree of saturation (Bishop's stress and suction) are examined. To solve the constitutive stress-strain equations, two stress integration procedures have been implemented, an explicit stress integration scheme with automatic substepping and error control techniques [2] and a fully implicit stress integration scheme based on the Backward-Euler algorithm with substepping [3]. Their performances during the integration of the constitutive laws are compared.