Bridges

This paper covers the complexities in design and construction of Southern Cross Drive Underbridge duplication as part of the Port Botany Rail Duplication project near Sydney Airport. The paper includes the implementation of temporary works design and the construction techniques required within the design to address the extreme space-related constraints from the airport operation as well as the traffic and rail operations.

The bridge duplication over Southern Cross Drive is a continuous two-span underbridge with a total length of 67m comprising a single-track trough girder bridge deck constructed entirely offline. Each span includes 2800mm deep post-tensioned concrete through girders and deck slab, with an overall superstructure width of 7100mm (including an allowance for refuges). Approach slabs, transition slabs and deflection walls are provided at the abutment locations.

Construction challenges included the curved plan alignment, very high skew to road below, extremely busy road below and the very low clearance above due to the restrictive Obstacle Limitation Space (OLS), imposed by Sydney Airport. A number of options were considered and discounted before the preferred solution was adopted to construct the superstructure in-situ on temporary falsework and lower it into position. The design included temporary falsework steel truss spans bridging over both of the three-lane carriageways to support the formwork. Both spans are similar with an approximate span length of 33 m and comprise side trusses supported on the abutment shelves of the proposed permanent works at one end and on temporary steel columns supported by the proposed permanent works pier pile cap on the other end.

The superstructure was constructed in-situ with the benefit of continuous access for all associated activities without disruption of the road traffic below. After deck post-tensioning and