Rock-crushing mechanism caused by TBM ball-tooth cutter in water jet slotting condition

To study the rock-crushing mechanism of the TBM ball-tooth cutter in water jet slotting condition, the rock-crushing process and phenomenon in slotting condition was simulated and observed with finite element simulation and experimental test, respectively. Then, the difference in rock-crushing features in varying slot depths and cut breadths were compared. The research findings indicate that the rock surface exhibits some intermittent pits in the cut trajectory while the ball-tooth cutter cut rock in slotting condition. For a certain slot depth, there exists a critical cut breadth within which the slotting condition has an auxiliary effect for the ball-tooth cutter. While the cut breadth is beyond the critical cut breadth, the auxiliary effect of the slotting condition will disappear. The critical cut breadths for the ball-tooth cutter at slot depths of 5 mm, 15 mm, 25 mm, and 35 mm are 20 mm, 30 mm, 30 mm, and 40 mm, respectively. At a certain slot depth condition, both the vertical and tangential loads rise then stabilize, but the side load firstly reduces and eventually stabilize with the growth of the cut breadth. Furthermore, the efficiency index initially grows with the growth of the cut breadth, but after reaching a peak, it begins to reduce and ultimately stabilizes. For each slot depth, there exists an optimal cut breadth that maximizes the efficiency index and enhances rock-crushing efficiency, and the optimal cut breadth corresponds to the critical cut breadth. Additionally, for a certain cut breadth which is below the critical cut breadth, both the vertical load and the tangential load tend to reduce, whereas the average side load and efficiency index of the ball-tooth cutter show an upward trend with the growth of slot depth from 5 mm to 35 mm. While for the certain cut breadth which is beyond the critical cut breadth, both the rock-crushing loads and efficiency index of the ball-tooth cutter under varying slot depth are similar. Overall, by the assist of water jet slotting condition, the rock-crushing loads and the efficiency index of the ball-tooth cutter could be evidently improved.