Principle of analysis of strain-softening rock mass and its application

In stress-strain curve, the process of decline of uniaxial stress at increasing strain is defined as strain-softening. Many types of geomaterials behave in strain-softening way in the case of disturbance of engineering activities. When the stress-strain relationship is described in mathematical formulation, the matrix of tangential elastic moduli is no longer positive-definite. Thereby difficulties arise in finding the solution to strain-softening problem. Strain-softening process is simplified into a series of brittle-plastic behavior; and solving brittle-plastic problem comes down to obtaining a series of brittle-plastic solutions. On the basis of classic plasticity theory, the method for analyzing strain- softening behaviour is proposed; and the corresponding solution process is implemented in finite element code. Furthermore, the influences of different strength-weakening modes on the distribution of plastic zone in the surrounding rock mass of a circular tunnel are studied. The longitudinal deformation profile (LDP) obtained by strain-softening constitutive model is also analyzed; and it is compared with the measurements in a tunnel. The preliminary numerical analyses indicate that the presented results look reasonable.