Experimental Study on Acoustic Emission Response and Damage Evolution Characteristics of Frozen Sandstone under Lateral Unloading

Abstract

Coal mine shaft excavation with the freezing method causes surrounding rock deformation under lateral unloading. In this paper, the failure process of frozen sandstone under lateral unloading was studied based on the acoustic emission (AE) response. The point where the deformation of rock samples under lateral unloading accelerates was taken as the plastic yield critical point (PYCP). The PYCP was defined as a fracture warning point. The mechanical properties of frozen rock samples under lateral unloading were also studied according to the AE response, and a damage model was established based on the number of cracks. The research showed that the number of cracks under lateral loading and cumulative acoustic emission energy in frozen sandstone increased slowly with time before the PYCP was reached and rose exponentially after the PYCP was reached. Following the sandstone (20°C) freezing, the peak stress under lateral unloading increased by 2.3–3 times and accounted for 52%–68% of the triaxial compressive strength. The peak stress increased with the initial confining pressure of the frozen rock sample, with a larger value indicating more severe damage. The model results were close to the experimental results before peak stress was reached, and the number of cracks could represent the damage degree and fracture level of the frozen sandstone.