Study on Progressive Damage and Failure of Sandstone Samples subjected to Cyclic Disturbance Loads using a Modified Triaxial Test System

The deep-buried rock may experience external disturbance loads and bear overstress simultaneously in the process of free surface formation of excavation. However, the mechanical behaviors and responses under these complex stress conditions are still poorly understood. The main purpose of this paper focuses on investigating effect of frequency and amplitude of external disturbance load on stress-strain behaviors of rock samples, progressive damage evolution and failure characteristics. Using a newly developed triaxial test system at Huaqiao University a series of disturbance tests with different frequencies (5 Hz, 10 Hz, and 20 Hz) and different amplitudes (1.0 MPa, 2.5 MPa, and 5.0 MPa) was carried out on sandstone samples at the axial stress level of 85% of uniaxial compressive strength. According to the experimental results, the frequency and amplitude of the axial disturbance stress have important effects on time duration until failure, and the changing trends of axial and radial strain versus time in disturbance loading phase are extremely similar with regime I and regime II transient creep and steady-state creepin idealized one-dimensional creep curve. Furthermore, damage variable defined in terms of residual strain method can well reflect the gradual increase in damage degree of rock samples in disturbance loading tests under different disturbance frequencies and different amplitudes conditions. The fragmentation degree and ductility characteristics of the failure of rock sample gradually increase with the disturbance frequency and amplitude.