The Acoustic Emission Behavior and Its Fractal Characteristics of the Sandstone Under the Disturbance Stress Paths

A series of mechanical tests and acoustic emission (AE) monitoring are conducted considering the disturbance stress paths, disturbance modes (low disturbance (LD) mode, medium disturbance (MD) mode, and high disturbance (HD) mode) and initial confining pressures (ICPs). The fractal dimensions of the AE temporal distribution (Dt) and spatial distribution ( Ds) are calculated, analyzed, and compared with the normalized AE count. The "sensitive effect", "inferior sensitive effect", and "delayed sensitive effect" of the disturbance mode can be observed through the temporal-spatial distribution of AE activities under the ICP of 12.5 MPa, 25 MPa, and 37.5 MPa, respectively. According to the normalized AE count, the damage of the disturbance modes under the ICP of 12.5 MPa, from serious to mild in proper order is HD, MD, and LD modes. The rapid increase in Dt and the sharp decrease in Ds appear in the MD and HD modes, respectively. This is in accordance with the "sensitive effect". Under an ICP of 25 MPa, only the HD mode can cause remarkable damage, as the evolution of the AE parameters does not vary obviously in the LD and MD modes, which can be regarded as the "inferior sensitive effect". Likewise, under an ICP of 37.5 MPa, each parameter presents a significant difference in the late period of DS among the three disturbance modes. This may correspond to the "delayed sensitive effect". The consistency in the occurrences of the discrepancy of the parameters indicates that the damage propagation and mechanical behavior of the engineering rocks are simultaneously dominated by the ICP and disturbance mode.