Rock mass unloading and relaxation has a great influence on the global safety degree of a project in high terrestrial stress region. In order to give a reasonable evaluation of the impact caused by relaxed rock mass, a new damage constitutive relation has been established systematically. Firstly, the internal variable in elastoviscoplastic theory has been used to establish the damage variable, by which the rock mechanical parameters pre- and post- damage can be obtained definitely. Then, based on the relaxation mechanism of rock mass and in light of mechanical parameters changes pre- and post- relaxation in each damage sub-step, a corresponding finite element algorithm for the evaluation of the relaxation effect is established and then the elasto-viscoplastic damage constitutive relation of relaxed rock mass could be derived. At last, the relaxation phenomenon in an underground tunnel is taken as an example for the validation of the proposed damage constitutive relation.
Rock mass unloading and relaxation is one of the most prominent problems during the engineering construction in high terrestrial stress region. The relaxation of rock mass can be regarded as a phenomenon of surface instability, with the main performance of rock burst, onion skin, appear tensional fissures which extend for a large scope and generally parallel with the excavated section, and also the deterioration of rock mechanical parameters is the salient feature of the relaxation process. Generally speaking, in addition to the rapid and small-scale disintegration of rock burst, the relaxation process is usually changing as time goes on, and the rock mass after damage still has some residual strength. In order to give a reasonable evaluation of the impact caused by relaxed rock mass on the global safety degree of a project, it is of great necessity to establish a corresponding algorithm considering relaxation effect.