Physico-mechanical Behaviors of Granite Under Coupled Static and Dynamic Cyclic Loadings

The stress distribution around constructions in deep rock can be modified by dynamic disturbances, such as earthquakes. For this, we proposed a new loading method applied to granite sample under coupled static and dynamic cyclic loading (CSDCL) condition. The variations in P-wave velocity, gas permeability, and mechanical properties of granite before and after CSDCL are revealed. It shows that with increasing axial static stress, the dynamic cyclic loading amplitude and cycle number, P-wave velocity, uniaxial compressive strength (UCS) and elastic modulus decrease, whilst the permeability and Poisson’s ratio increase. It seems that variations in those parameters have a close relation with the exciting frequency. In this case, CSDCL is applied for crack development along the axial direction in the rock samples, and subsequently results in degradation of mechanical properties, delay of P-wave propagation, and increase of the transport paths. The results show that the permeability and Poisson’s ratio are likely to be more sensitive to the CSDCL, in particular under the axial static stress. The empirical relationships of the P-wave velocity with permeability, UCS, and elastic modulus are established for a pragmatic monitoring purpose. From design point of view, we have established the relationships of the disturbance factors to damage variable. Then the correlations of the damage variable to permeability, UCS, and elastic modulus are analyzed. The testing results in this context could facilitate our understanding of rock stability upon excavation subjected to dynamic disturbances.