Discrete Fracture Network Modelling for a Shallow Cover Road Tunnel System

Abstract The city of Sydney (Australia) is currently undergoing a major infrastructure construction boom, with numerous rail and road tunnels currently under construction. This paper presents DFN modelling undertaken as part of the tunnel design process for a major road tunnel system in western Sydney. The primary discontinuities controlling block formation are expected to be joints, bedding planes and seams / bedding plane shears, which were included in the DFN model. This paper presents the necessary input parameters for the modelling and derivation of these parameters, along with the model generation process. Multiple realizations of the model were generated, with a stability analysis carried out on each. Given the complicated geometry of the tunnels in the project two representative 100 m lengths of tunnel geometries were analyzed; a wide span cavern (striking 020°) and a mined tunnel (striking 125°). The stability analyses were used to develop the unstable block volume distribution and identify the maximum likely block volume for the crown and sidewalls of the cavern. In addition, the block results were filtered relative to the proposed pattern rock bolting to assist designers with considering shotcrete loads.