Abstract：Triaxial cyclic loading-unloading tests on Beishan granite from deep underground were conducted using the rock mechanical test system MTS815 to investigate the variation of strength parameters of the rock. The variation characteristics of rock strength parameters were discussed in detail according to the Mohr-Coulomb theory. The measured complete stress-strain curves under the different confining stresses were analyzed. The plastic shear strain was regarded as the plastic parameter to describe the strength and dilation behaviors of rock. The results indicate that the damage stress can be regarded as the zero point of plastic parameter and as the start point of the strength parameter variation. When applied stress is larger than the damage stress，the cohesion of the rock decreases exponentially with increasing the plastic parameter and finally approaches zero. Meanwhile，the frictional angle increases to the peak value and then decreases gradually to a constant value as the plastic parameter increases. The logarithmic normal distribution can be used to fit the data. The dilation behavior of the rock after the damage stress is similar to that of the post-peak stage. The dilation angle decreases with increasing plastic deformation and confining stresses，and is sensitive under the low confining pressures. The established models were implemented in the numerical software(FLAC) to simulate the triaxial compression tests. The predictions reproduced the main features of actual mechanical and dilation behaviors of Beishan granite.
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2017, Vol. 36 
