Abstract: In order to evaluate the rock breaking mechanism and to consider the effect of free surface in the tunnel excavation, a series of Universal Distinct Element Code (UDEC) models are established simulating the process of rock fragmentation by Tunnel Boring Machine (TBM) cutters. The analysis shows that, if an appropriate TBM cutter distance and penetration are maintained due to the existing of the adjacent free surfaces, the crack propagation energy decreases; the density of the cracks increases, cracks are prone to be initiated. Therefore, the rock mass are easier to be disintegrated and the efficiency of the cutters can be improved.

Key words: TBM, Disc Cutter, Rock Breaking, UDEC, Free Surface