AN ELASTOPLASTIC CONSTITUTIVE MODEL FOR SOFT ROCK WITH STRAIN-SOFTENING

Dense sands, overconsolidated clays and soft rocks exhibit strain-hardening and strain-softening behaviour in a certain range of confining pressure. The aim of the present paper is to construct a constitutive model of soft rock that can describe not only the strain-hardening behaviour, but also the strain-softening behaviour. An elasto-plastic constitutive model for soft rock is derived by introducing a stress history tensor.* The model is evaluated through a comparison of the calculated results and the experimental results of tests on sedimentary soft rock (porous tuff). In addition, the applicability of the model to numerical analyses is discussed in relation to the uniqueness of the solution in initial and boundary value problems.