The Influence of the Rotary Speed of a Microwave Applicator on Hard-Rock Fracturing Effect.

Microwave-induced hard rock fracturing technology has potential application prospects in tunnel boring machine (TBM) hard tunnel excavation. It is of great significance to research the hard rock cracking induced by rotary microwave applicator irradiation to promote the application of microwave–TBM coupling. Based on a rotary open microwave irradiation hard rock fracturing true triaxial test system independently developed by Northeastern University, Chifeng basalt is taken as the research object. The crack propagation characteristics of hard rock irradiated by a microwave applicator at different rotation speeds under the conditions of no stress and true triaxial stress are studied, and the fracturing mechanism of hard rock irradiated by rotary microwave applicator is revealed. The results show that the temperature in the same area of hard rock rises in a "step shape" under rotary microwave applicator irradiation. The faster the microwave applicator rotation speed is, the shorter the intermittent irradiation time of the same area of hard rock, the quicker the temperature rise is, and the earlier the hard rock cracking time is first detected. The degree of crack propagation and the decrease in compressional wave velocity are positively correlated with the microwave applicator rotation speed. In the process of rotary microwave applicator irradiation, the cracks in the irradiated hard rock surface develop and expand from the high principal strain region at the boundary to the central region of the irradiated surface. Under the condition of no stress, tensile failure in hard rock is induced by rotary microwave applicator irradiation. Under the condition of true triaxial stress, tensile failure induced by rotary microwave applicator irradiation mainly occurs in hard rock, although shear failure occurs at the same time. This makes the crack development in the irradiated hard rock surface denser and the crack network more complex. This research provides a new perspective for microwave–TBM coupled tunneling in hard rock tunnel engineering. Highlights: A rotary open microwave irradiation hard rock fracturing system is developed independently. The influence of microwave applicator rotation speed on cracking effect of hard rock under a true triaxial stress condition is studied. The fracturing mechanism of hard rock irradiated by rotary microwave applicator is revealed. This study provides a new perspective for microwave–TBM coupled rock breaking in hard rock engineering. [ABSTRACT FROM AUTHOR]