Physical and numerical studies of rock fragmentation subject to wedge cutter indentation in the mixed ground

To study the effects of the mixed ground conditions on the cutter force and failure pattern during the tunnel boring machine (TBM) excavation, rock cutting tests under wedge cutter are conducted both in the physical experiments and the bonded particle model (BPM) numerical simulations. The results of simulation are generally comparable with those of experiments under single cutter. It demonstrates that the softer bottom material causes more disperse stress distribution which leads to wider AE accumulated area and more rapid displacement change in the indentation direction. Further simulations are conducted under double cutters. Crack may propagate deeper into the specimen due to the weaker bottom material. When the inclination of the material interface changes, the failure pattern of the specimen becomes highly asymmetric and the forces of the two cutters are not equal any more. Frequent change of ground conditions causes high asymmetric cutter force distribution, frequent changing cutter force as well as high eccentric moments on the cutter head.