Abstract: In order to illuminate the anisotropic rheological characteristics and the damage evolution of quartz-mica schist from Danba Hydropower Station, the stress relaxation tests are carried out for the mica-quartz schist samples, which were divided into the parallel group and the vertical group. Each of these samples sustained the different loads for almost 720 hours on the program-controlled creep test instruments. The test results show that the relaxed process contains three phases, i.e. rapid relaxation phase, slow relaxation phase and steady-state relaxation phase, and is non-fully damped relaxation. This conclusion is suitable for both parallel and vertical groups. And the difference exists in that the damped duration of the parallel group is longer than that of the vertical, because of the influence of schistosity direction. Furthermore, based on the relaxation characteristics of mica-quartz schist, the rheological constitutive equation of Bingham model are improved by introducing the damage factor of dissipated energy into the equation. And the stress relaxation equation are derived by the modified Euler method of finite difference, in order to identify the parameters of the improved model for the mica-quartz schist by the method of integrating artificial neural network. The results demonstrate that at the rapid relaxation phase, the damage evolution develops very fast and damage rate decreases with the relaxation processes, which is also fit for both parallel and vertical groups and is parallel to stress relaxation. In addition, it is obvious that the theoretical solution is highly consistent with the test data. So it means that the improved model can well describe the relaxation properties of mica-quartz schist, so as to provide significant guidance for the soft rock engineering.

Key words: mica-quartz schist, stress relaxation, damage evolution, Bingham model