Abstract
In this paper, an elasto-viscoplastic constitutive model with strain softening is proposed based on Adachi-Oka's model. In the model, a time measure, instead of strain measure adopted in a previous model, is introduced as an internal variable to account for not only stress history but also time change. The yielding function is defined in the way that the structural deterioration of geologic materials with time is considered. The application of the model to the experimental results for soft sedimentary rock indicates that the model can not only describe the time dependency, such as strain rate dependency, creep and stress relaxation to some extent, but also the strain softening behavior of geologic materials.
