Cracking and Creep Behavior of Rocks Considering Propagation and Interaction of Adjacent Cracks Under Hydro-Mechanical Coupling

The sub-critical propagation and interaction of cracks are important factors affecting the cracking and creep behavior of rocks, especially under the long-term coupling effect of the geo-stress and groundwater. The multi-stepped triaxial creep tests were conducted by using the mortar specimen containing two connected cracks to investigate the time-dependent fracture and mechanical characteristics of rocks under hydro-mechanical coupling. A creep rate model for rocks was proposed taking into account the sub-critical propagation and interaction effect of cracks, and the corresponding parameters were analyzed by comparing the test data. The results showed that: the mortar specimen containing adjacent cracks presented a tensile-shear failure mode; Due to the influences of water pressure and crack interaction, only one crack propagated and formed macro fracture, while another crack was inhibited; the proposed creep rate model reflected well the crack propagation and interaction effect, and it was suitable to describe the rock creep with good accuracy; the interaction effect between cracks decreased with the increase of deviatoric stress, and the 45° cracks had the strongest inhibition effect on the adjacent crack; the rocks entered a stable creep stage quickly under the lower stress condition, while the creep rate decayed slower under higher stress conditions; the transition time was shorter for the rocks containing 45° cracks, due to its larger creep rate during the stable state.