Abstract: The full-section tunnel-boring machine(TBM) is widely used in the tunnel construction due to many advantages include high efficiency, safety and environmental protection etc. The rock breaking mechanism of the TBM cutter is the essence deciding the design and construction of TBM. The rock will break when it interacts with the TBM cutter. The discrete element method (DEM) has become an effective means to study the rock breaking mechanism of the cutter. However, the dimension of the numerical model generated by most discrete element softwares is relatively small and the simplified two-dimensional models are always applied, which has an obvious size effect. The MatDEM software based on discrete element method is used to construct a large-scale 3D model of rock breaking cutter, thus simulating the real rock breaking process of the cutter. The clustering unit is used to simulate the rigid cutter, which can realize the dynamic process of rock breaking under different conditions using the double cutters. The forces of cutters during the rock breaking process can be monitored, and the force model of cutters and variation of specific energy (SE) under different cutters spacing/penetration ratio (S/P) are calculated and analyzed. The simulation results show that the cutting force is a complex and irregular impact load during the rock breaking process. It is related with the cutting parameters, rock properties etc. The increase in the penetration depth and the cutters spacing requires a much higher force to break the rock. For a specific rock, there is an optimal ratio of the spacing/penetration degree, making the minimum SE for rock breaking. The MatDEM software can better simulate the rock breaking process of the cutter, which matches well with the indoor linear cutting test, thus it is beneficial to comprehensively explore the rock breaking mechanism.

Key words: full-section tunnel-boring machine(TBM), rock breaking mechanism, MatDEM software, cutting force, discrete element