Experimental study of energy and frequency characteristics of acoustic emissions induced from tensile and shear cracks in tunnel rockburst process

Abstract

Studying the characteristics of tensile and shear cracks in a rockburst event is crucial for understanding the rockburst mechanism. In this study, several specimens were tested under biaxial compression, and the released acoustic emissions (AEs) of the resulting tunnel rockburst event were recorded. Based on the AE energy and dominant frequency parameters, the different AE characteristics and dominant frequency evolution law of tensile and shear cracks during the rockburst were analysed. According to the results, there are four types of AE signals in a rockburst event: low-frequency and low-energy signals, low-frequency and high-energy signals, medium-frequency and low-energy signals and high-frequency and low-energy signals. The low-frequency and low-energy signals are mainly generated by tensile cracks, and the low-frequency and high-energy signals originate from both tensile and shear cracks. The medium-frequency and low-energy signals and high-frequency and low-energy signals are often generated by tension cracks. The rockburst process can be classified into four stages: calm period, small-grain ejection period, sheet-like peeling period and violent ejection period. Before the occurrence of rockburst, both tensile and shear cracks produce low-frequency and high-energy signals. The low-frequency and high-energy (amplitude) AE signals are crucial for monitoring and early warning procedures for rockburst events.