Experimental investigation on rock breaking by the TBM cutter assisted with the laser-induced groove

Tunnel boring machines (TBMs) have been increasingly applied in extreme regions such as "Three highs" (high confining pressure, high rock hardness and high quartz content), researchers have introduced laser technology to the TBM field to improve cutting efficiency. The aim of this study is to investigate the effect of laser power, laser moving speed, blade width, distance between the cutter and laser-induced groove (DCLG), and edge angle on rock breakage after coupling the laser with TBM cutter-head, and obtain the optimal combination of these parameters. Two sets of indentation tests were conducted: one with the assistance of laser-induced grooves (LG) based on a L18(37) orthogonal design table; the other was a controlled trial without the laser. The corrected indentation hardness index (CIHI), specific energy (SE) and penetration force were utilized as performance indicators to comprehensively evaluate the experimental results. Additionally, a new method proposed in this paper allowed for accurate measurement of the volume of rock debris, avoiding the difficulties associated with the traditional weighing method, which requires collecting rock fragments caused by rock bursts. Finally, variance analysis, range analysis, and comprehensive evaluation analysis were performed on the three performance indicators. Results show that LG can greatly reduce the penetration force of the cutter and improve cutting efficiency. The primary and secondary factors affecting the rock breaking performance of a laser-assisted cutter are: blade width, DCLG, laser moving speed, laser power and edge angle, and the optimal combination of rock-breaking parameters: The blade width is equal to 3 mm, the DCLG is equal to 5 mm, the laser moving speed is equal to 2 mm/s, the laser power is equal to 20 W, and the edge angle is equal to 12 degrees.