Computer modelling and roof support design for large diameter road tunnels in Sydney Hawkesbury sandstone

This paper looks at the design of the roof support systems for the M2 tollway twin tunnels located at Epping in Sydney, Australia. The tunnels pass through Hawkesbury Sandstone which is subject to high insitu horizontal stresses. Making use of a finite difference computer modelling program, the tunnel excavations were simulated on computer and the results predicted that differential movements could occur along horizontal bedding planes in the sandstone, immediately above the tunnel crown. These movements, caused by the high horizontal stresses became an important factor in the design of roof rock bolts.