ABSTRACT
This paper presents a study case on how a design solution with lower carbon footprint was achieved at a road tunnel crossover connecting two major stages of Australia’s largest road tunnel, the WestConnex Project. There was only a 3 m thick crown rock pillar (i.e., vertical separation) between the crossover ramp and twin mainline tunnels. Two bridging structures were initially designed to be cast in the mainline tunnels. These structures need to be heavily reinforced with concrete thicknesses up to 2 m extending for up to 100 m in length. Constructing these large structures underground is challenging, increasing the use of materials and reducing production rates. A new approach allowed for replacing one of these bridging structures with a Permanent Sprayed Concrete Lining combined with temporary rock reinforcement. Further, extensive in-tunnel monitoring combined with a specific construction sequence was proposed to minimise the risks of roof rock pillar failure. The in-tunnel displacements obtained from the monitoring data were then compared with the numerical predictions. Similar trends were observed between measured and predicted in-tunnel displacements, validating the design.
