Experimental and numerical simulation study on the relationship between cutting depth of high-pressure water jet with high traverse speed and disc cutter penetration of TBM in hard rock tunnel

The disc cutting load of a TBM is insufficient to induce crack propagation in hard rock tunnels due to the high strength of the rock. High-pressure water jets, considered an auxiliary rock-breaking method, enhance the disc cutter's capacity to penetrate cracks by creating pre-existing fissures. In order to examine the correlation between cutting depth achieved by a high-pressure water jet operating at high traverse speeds and the penetration capability of TBM disc cutters, we conducted rock cutting experiments employing varying traverse velocities for the water jet. Additionally, we performed linear disc cutting experiments using full-size disc cutters equipped with grooves. These experiments were conducted using high-strength granite from China's Bei Shan region. We utilized the Discrete Element Software PFC2D to construct a rock breaking model based on Tyson polygons, enabling us to investigate the microfine influence mechanism of grooves with symmetry. The experiments involving high-pressure water jet grooving at high traverse velocities revealed a logarithmic decrease in groove depth as the nozzle's traverse velocity increased. These findings suggest that when high-pressure water jets are employed as an auxiliary method in TBM operations, increased distance from the center of the disc hob leads to higher traverse velocities, resulting in less efficient rock breaking. Nonetheless, increasing the nozzle diameter can enhance the rock-breaking effect. Linear disc cutting experiments indicate that, at a penetration depth of 4 mm, grooves with depths less than 4 mm have minimal impact on assisting in disc cutter rock breaking. However, when the groove depth exceeds 4 mm, there is a noticeable improvement in the disc cutter's breaking performance. The numerical simulation results provide initial validation for the linear disc cutting experiment. Lastly, considering the specific conditions of the Beishan tunnel, we propose a design scheme that involves the zoned arrangement of water jets. Additionally, we recommend appropriately reducing the rotational speed when employing high-pressure water jets as an auxiliary method for rock breaking. The research findings presented in this paper can serve as valuable references for the design and implementation of high-pressure water jet-assisted TBM cutter rock breaking.