AN ELASTOPLASTIC CONSTITUTIVE MODEL FOR SOFT ROCK WITH STRAIN-SOFTENING

Dense sands, overconsolidated clays and soft rocks exhibit strain-hard ening and strain-softening behaviour in a certain range of confining p ressure. The aim of the present paper is to construct a constitutive m odel of soft rock that can describe not only the strain-hardening beha viour, but also the strain-softening behaviour. An elasto-plastic cons titutive model for soft rock is derived by introducing a stress histor y tensor. The model is evaluated through a comparison of the calculat ed results and the experimental results of tests on sedimentary soft r ock (porous tuff). In addition, the applicability of the model to nume rical analyses is discussed in relation to the uniqueness of the solut ion in initial and boundary value problems.