The deep surrounding rock under true triaxial stress is easy to break at the new excavation face, which will induce engineering disasters to threaten personnel and equipment. Many studies have shown that the intermediate principal stress (IPS) has a great influence on rock failure. To accurately understand the influence of IPS on the gradual failure mechanism of the new excavation face under true triaxial stress and extract the key precursor information of rock failure, this study is based on true triaxial tests of acoustic emission (AE) monitoring, which provides a creative explanation to the phenomenon that sometimes the sudden increase of the AE counts rate (ACR) and the energy release rate (ERR) changes asynchronously. This paper analyzes the influence of IPS on the crack type in the failure process, studies the transitional behavior and gradual evolution of AE dominant frequency, and presents the precursor information index for rock failure. The results show that the sudden increase times of ACR and ERR under different IPS values are different. The rock under lower IPS is prone to produce intergranular fracture with low energy consumption, while the rock under higher IPS is prone to produce transgranular fracture with high energy consumption. Near the peak stress, the dominant frequency at lower IPS shows obvious downward transitional behavior, and the dominant frequency under higher IPS presents downward and upward transitional behavior. This study verified that $t_{\mathrm{III}-\max }$ can be used as the key precursor information for predicting rock failure.

High energy consumption in ore crushing brings great challenges to the mining industry. Microwave irradiation provides a promising solution for rock breaking. However, there is currently a lack of detailed understanding of the microwave parameters regarding magnetite ore. The purpose of this study is to fully understand the potential value of microwave irradiation applied in auxiliary crushing of magnetite ore. It is typically found that increasing power reduces the mechanical properties of ore, increasing energy utilization, and crushing degree, more than extending time. Based on wave impedance, this reveals the dependence of energy utilization on thermal damage. Increasing irradiation power, time and cooling rate will cause more transgranular cracks and cleavage tears in the crushed ore. Based on the separate microwave response of several minerals, the microwave-damage mechanism of magnetite ore is further demonstrated.