Failure characteristics of microwave heat-treated stressed sandstone: Implications for deep rock breakage using TBM cutting

Microwave-assisted rock fragmentation is a clean, safe, and economically viable method in deep energy development. The innovation of this study lies in the first investigation of rock breaking under initial stress using microwave-assisted tunnel boring machines (TBM) cutters. To overcome the problem of inaccurate monitoring of crack information in laboratory tests, a new concept was adopted to simulate the failure process of microwaveirradiated sandstone caused by a TBM cutter. The microscopic parameters of the model were calibrated based on the laboratory test results. The results showed that an increase in the microwave power led to an increase in the damage level of the sandstone. The dominant failure modes at a low initial stress were vertical and diagonal cracks. At a high initial stress, the failure modes were a combination of vertical, diagonal, and subhorizontal cracks. The critical range of the initial stress to inhibit crack expansion was 10-20 MPa. The rock-breaking efficiency was negatively correlated with initial stress and positively correlated with microwave power. The assisted rock-breaking effect of microwave power was evident at 30 MPa. These results serve as a guide for selecting the appropriate microwave power for rock-breaking under initial stresses.