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

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 01 and 02 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 01 and 02 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 01 and 02 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 degrees C (average about 172 degrees C). The relationship between thermal fracture and stress provides guidance for parameter design.