When tunnels are constructed near existing structures or on shallow soft ground there is possibility of very large deformations of the ground. These deformations may in turn cause failure of the tunnel as well as adjoining structures. Also another primary design issue of tunnels is the determination of stress levels associated with the yield of wall due to excavation. Hence proper steps should be taken to ensure the safety of the tunnel by providing suitable supports and reinforcement. Since the ground behaviour is not properly understood, it is necessary to estimate the appropriate support and reinforcement and their response through numerical modelling. In this study, several simulations have been done to understand the effect of excavation for tunnels on a soft ground through numerical modeling by discrete element method (DEM). The numerical simulations adopting discrete element method predicts the mechanical behaviour of soil/rock masses through grain scale modelling. Here, a three dimensional ground surface is modelled in a weak rock like sandstone and a tunnel is excavated inside the modelled ground surface. The response of the system after excavating the tunnel is studied for various cases viz. tunnel without any support or lining, tunnel with lining alone and tunnel with both lining and reinforcement. The studies clearly indicate that the tunnel without any lining on this considered weak rock fails immediately and the stability considerably improves with lining and reinforcement.
