Structural degradation and fracture behavior of granite after microwave irradiation: Assisted hard rock breaking

Non-blasting excavation (such as mechanical rock breaking) of underground rock mass engineering can effectively avoid blasting vibration damage of surrounding rock. However, there are significant tool wear problems in mechanical excavation of hard rock. Microwave-assisted mechanical rock breaking is considered as a promising method in recent years. The existing results focus on analyzing the impact of microwave irradiation on the physical and mechanical properties of rocks, with scant attention given to the fracture behavior of rocks. The novelty of this study is that it reveals the effect of microwave irradiation on the structural degradation of granite, and obtains the characterization results of crack evolution inside the rock. The results show that increasing the microwave power will induce more transgranular fractures. Microwave irradiation will increase the content of cross-scale pores by degrading the rock microstructure. Increasing the power will cause more surges in AE counts rate (ACR) during active phase. There is a quiet period before rock failure, and microwave irradiation can only shorten the quiet period, but not eliminate it. The existence of quiet period has no connection with the thermal damage state. The 5.5 kW is a key parameter because it leads to the disappearance of micropores and original cracks.