ABSTRACT
Since Roscoe et al. proposed the Cam-clay model last century, a large number of classical and practical elastoplastic constitutive models of clay, aiming to describe the compressive hardening, shear dilatancy and structural behaviors of clay comprehensively, have been proposed on the basis of large amounts of experimental data obtained at the strain rate about 10−710−5s−1. However, geotechnical engineers sometimes are very interested in the long-term deformation and strength characteristics of earth structure deforming at the strain rate about 10−11-10−8s−1. In order to predict the time-dependent behavior of clay at different strain rate, various elastic-viscoplastic constitutive models (e.g.Adachi & Oka 1982, Kutter & Sathialingam 1992, Hinchberger & Rowe 1998) have been proposed based on the overstress theory of Perzyna (1963). But these models are usually not able to describe the complicated deformation behavior of the overconsolidated or structural clay as the existing advanced elastoplastic models (e.g. Hashiguchi 1989, Asaoka et al. 1998, 2000). In recent years, some researchers (e.g. Rocchi et al. 2003, Kimoto & Oka 2005, Hinchberger et al. 2009,Yin et al. 2011) also proposed the advanced elastic-viscoplastic models, which can model the rate-dependent behavior
and structured characteristics of natural clay, but these models are either too complicated to understand for the engineers, or not easy to be implemented into finite-element code. In this paper, three existing classical elastoplastic constitutive models, i.e. Cam-clay model, subloading surface model and superloading surface model, are improved to predict time-dependent behavior of the normally consolidated, overconsolidated, or structured clay, respectively. These proposed models are easy to understand, and their stress integration algorithms are also present, which make the new models convenient to be implemented into the finite element software such as ABAQUS.
