TBM-cutter rock-breaking effect and mechanism considering different cutting sequences

For a tunnel boring machine (TBM), the cutter rock-breaking effect and mechanism are key components of the machine design and construction. Each cutter on the TBM cutterhead is affected by adjacent cutters and exhibits different rock-breaking effects under different rock-breaking sequences. Considering the influence of two adjacent cutters, the target cutter has three rock-breaking sequences, A–C, for which the target cutter cuts as the second, first, or last tool, respectively. Most previous studies considered the sequential rock-breaking method, i.e., sequence A, and ignored jumping rock-breaking, i.e., sequences B and C. To quantify the obvious differences in rock-breaking effects between jumping and sequential rock-breaking, and to analyze the jumping rock-breaking mechanism itself, a series of special experiments was performed in this work. The experiment results show that, in terms of the rock-breaking force and boreability index values, the order is sequence B > A > C. For the specific energy, when the penetration is greater than the optimal penetration of the sequence C, the order is sequence B < A < C. These differences in rock-breaking effects can be reasonably explained from the perspective of pre-damage using the crack development method. As jumping rock-breaking constitutes a considerable proportion of the TBM cutter operation, consideration of this mechanism with its unique rock-breaking characteristics provides new directions for fine-tuning the design of TBM cutterheads and selection of TBM construction parameters.