Distinct element method analysis of jointed rock fragmentation induced by TBM cutting

The mechanism of rock breaking and optimal design of the cutters are especially significant in tunnel excavation by Tunnel Boring Machine (TBM). In order to investigate the jointed rock fragmentation induced by TBM cutting, and to improve the capability and efficiency in rock breaking, a series models of jointed rock cutting were simulated by the Distinct Element Method, where an improved zero-thickness bond contact model was implanted to capture the main mechanical behaviour of the hard and brittle rocks. The fragmentation of intact and jointed rock induced by TBM cutting with double cutters was simulated to investigate the influence of jointed angle, spacing and cutter penetration depth on the rock breaking. The main results show that: the process of intact rock or jointed rock fragmentation can be divided into loading stage, unloading stage and residual leaping broken stage and the existence of the joint will make unloading phase in advance; the failure modes for jointed rock breaking can be classified into four types: joint-prevent failure mode, joint-propagation failure mode, joint-tendency failure mode and joint-initiation failure mode; the optimum cutter spacing can be found in the process of jointed rock fragmentation. The result will be useful in the optimisation design of cutters and estimation of penetration depth.