Engineering

Breakage

Geotechnical engineering

Materials science

Computer simulation

Overburden pressure

Distribution (mathematics)

Geology

Fractal

Physics

Finite element method

Simulation

Mathematics

Fractal dimension

Mathematical analysis

Geometry

Composite material

Structural engineering

Discrete element method

Mechanics

Tunnelling and Underground Space Technology

Confining pressure is an important factor that affects the rock breakage efficiency of Tunnel Boring Machines (TBMs). This study analyses the influence of the confining pressure on the rock breakage process, rock breakage efficiency and fragmentation distribution after crushing using a coupled FEM-DEM method. First, the parameters of the rock numerical model are calibrated using numerical uniaxial compression tests and Brazilian tests. Second, the rock breakage by the cutter is simulated under different confining pressures, and the influence of the confining pressure on the rock breakage process is determined. Third, using a post-processing program developed for extracting the induced fragments, the distribution of fragments after rock fragmentation is obtained, which accurately provides the fractured area of the rock to determine the variation of the specific energy (SE) with confining pressure. Finally, the equivalent length distributions of the fragments are analysed using the fractal method. The results show that the confining pressure has a significant inhibitory effect on the propagation of median cracks. The angle of the lateral crack increases with increasing confining pressure, and the length of the crack first increases and then decreases. The maximum normal force and the maximum indentation distance also increase first and then decrease with increasing confining pressure. The SE first increases with increasing confining pressure; however, when the confining pressure reaches the first critical value, the SE begins to decrease with increasing confining pressure and then continues to increase after the confining pressure reaches the second critical value. The variation of the fractal dimension with the confining pressure is similar to the variation of the SE with the confining pressure.

Numerical study of the effect of confining pressure on the rock breakage efficiency and fragment size distribution of a TBM cutter using a coupled FEM-DEM method