Acoustic Emission Location Accuracy and Spatial Evolution Characteristics of Granite Fracture in Complex Stress Conditions

Microseismic/acoustic emission (MS/AE) location technology is a powerful means to study the spatial evolution characteristics of rock fracture and early warning of geological hazards. This paper investigated the variation in MS/AE location accuracy and the spatial evolution characteristics of granite fracture in complex stress conditions by using the velocity-free MS/AE source location method. Results show that the variation of wave velocity caused by granite fracture is a key factor for the variation of location accuracy. It is expected to improve the location accuracy by dynamically correcting the iterative wave velocity. The evolution process and results of granite microcracks in uniaxial and biaxial stress conditions show consistency and difference. The consistency is that the microcracks start from the edges and corners at both ends of the rock and gradually develop to the central side of the rock. The distribution of AE events changes from scattered to clustered, nucleated, and finally to banded distribution. The difference is that the advance of rock damage strain point and the macroscopic fracture surfaces are mostly perpendicular to the minimum principal stress direction in biaxial stress conditions. This paper is not only a useful supplement to the MS/AE location methods and theories, but also provides a reference for the disaster-causing mechanism of rock instability as well as disaster prevention and control.