The characteristics and mechanism of microwave-induced borehole fracturing of hard rock under true triaxial stress

• Published in: Engineering geology 2022-09, Vol.306, p.106768, Article 106768
• Main Authors: Zhang, Jiuyu, Feng, Xia-ting, Yang, Chengxiang, Lin, Feng, Li, Shiping, Tong, Tianyang, Su, Xiangxin
• Format: Article
• Language: English
• Subjects: Deep hard rock engineering; Destressing; Microwave-induced borehole fracturing; Rockburst; True triaxial stress
• ISSN: 0013-7952; 1872-6917
• DOI: 10.1016/j.enggeo.2022.106768

High stress induced by excavation disturbance in deep hard rock engineering can cause rockburst accidents. Microwave-induced borehole fracturing of hard rock is a promising technique for preventing rockbursts, the principle of which is to reduce energy and stress concentration levels in rock mass through microwave heating. The characteristics and mechanism of microwave-induced borehole fracturing of hard rock under different true triaxial stresses were experimentally investigated. After microwave-induced borehole fracturing under different σ1 and σ2 conditions, a complex crack network dominated by tensile cracks was generated in the rock specimen, which is consistent with the results obtained by AF and RA. According to the P-wave velocity before and after the test, the degree of thermal fracture is positively linearly correlated with σ1 and σ2 as a whole, and has good consistency with the length and number of thermal cracks. The results show that the technique will have better applicability and higher fracturing efficiency in high-stress areas. The thermal fracture process of basalt specimens under different σ1 and σ2 conditions is similar, which can be divided into a silent period, quiet period, dense period, and persistent period. In addition, thermal fracture exerts a significant threshold temperature effect, and fracture rate increases rapidly when the temperature reaches 150–192 °C (average about 172 °C). The relationship between thermal fracture and stress provides guidance for parameter design. •Microwave-induced borehole fracturing of hard rock is a promising technique for preventing rockbursts.•Microwave-induced borehole fracturing tests are conducted under different true triaxial stress.•The characteristics and mechanism of microwave-induced borehole fracturing under different σ1 and σ2 conditions are investigated.•Microwave-induced borehole fracturing process is investigated by AE technique.