Numerical study on effects of confining stress on rock fragmentation by TBM cutters

A novel meshless numerical method known as general particle dynamics (GPD) is used to study the effects of confining stresses on rock fragmentation by TBM cutters. The processes and modes of rock fragmentation and the diggability by TBM cutters under confining pressures of 0, 5, 10, 15 and 20 MPa are studied. The following results are obtained: (1) The confining stress is adverse to the propagation of the central cracks during the process of rock fragmentation. (2) With the increasing confining stress, the propagation direction of the Hertz cracks between two cutters changes, and the angle of cracks decreases. (3) Under the same penetration, the crack initiation forces and the diggability index significantly increase with the increasing confining stress. Moreover, the GPD method is introduced to the tunnels in the Jinping Ⅱ Hydropower Station, and the influcnces of high geostress on rock fragmentation are analyzed and plate cracking is discovered. The analysis results show that if the plate cracking is caused by high geostress, the geostress promotes the rock fragmentation by TBM cutters.