Study on the influence of joint dip angle and spacing on rock fragmentation by TBM double disc cutters

Tunnel boring machines’ construction efficiency is significantly affected by the formation of joints. Indentation tests were performed to explore the influence of joints on rock fragmentation by double cutters on a gray sandstone. The process of rock fragmentation was captured by the digital image correlation method. Simulations based on the cohesive element with zero thickness were then conducted to simulate the failure process and evolution of jointed rock under the action of double cutters. A mechanical model is established to deduce the stress evolution in a rock mass by double disc cutters with different penetration depths. The action mechanism and mechanical influence of joints on rock fragmentation were determined. The results show that, under the action of double cutters, the rock with joints is more ready broken than the intact rock mass. The joint acts as a weak interface in the rock mass. Finally, the rock mass is destroyed along the vertical joint, forming rock slag with the joint as the boundary. When the joint dip angle is about 30°, the interaction force between the rock mass and the cutter is low, and the rock fragmentation efficiency is high. And the spacing of joints is also a key factor in the rock-breaking efficiency of double cutters.