ABSTRACT
The Five Dock Station site is a planned metro station for the Sydney Metro West project and lies in a high-density residential zone. The reference design planned the station as binocular-shaped mined caverns with two station shafts at either end to minimise the impact of surface settlement. The Design and Construct contract designers replaced the concept of binocular-shaped caverns with a single large-span mined cavern based on an assessment using more rigorous rock mechanics principles and discontinuum modelling using UDEC and 3DEC. This design solution provided a large open space that appealed to passenger use, and the client received it well. To minimise the cavern crown deflection and surface settlement, an approach named “coat hanger” was adopted by installing longer CT bolts as a secondary bolting system to the primary ground support. The paper also discusses the challenges associated with high horizontal in-situ stresses during the cavern excavation. Finally, numerical back analysis was performed to evaluate the conditions encountered and compare them to the expected primary support performance and cavern stability. The design approach proved effective, as the measured surface settlements and in-tunnel movements matched the design predictions.
