Bridges

Built in 1921, the existing bridge is a two-span (6.4m & 9.45m) Jack Arch superstructure supported on unreinforced masonry abutments and central pier. The bridge spans over the railway line and carries two lanes of traffic with narrow footways along both edges. The abutments act as retaining structures that are partially propped at the top by the superstructure.

Road traffic required this bridge to be widened to accommodate four lanes of traffic and tie-in to the existing roads at each end. Rail traffic required the bridge to accommodate future addition of two rail tracks and increased vertical clearance for overhead wiring maintenance.

The final design allows for the demolition of the existing bridge and provision of a new single span bridge. The envelope and clearances as determined by Auburn Council and Sydney Trains have been adhered to in the design.

The new deck consists of steel WC girders with cast-in-situ concrete deck slab. The abutments consist of concrete headstocks over bored piles built behind the existing abutments. Steel girders were selected and the deck slab built integral with the abutments to maximize vertical clearance.

Construction is only allowed two weekend track possessions with the second possession provided as allowance in case construction went behind schedule. Prior to first possession, the new abutments were built. On the first possession, the superstructure and central pier of the existing bridge was demolished and the new girders installed. The edge girders came with precast fascia panels to serve as safety railing during construction. Second possession tasks include the demolition of the existing bridge abutments and finishing the new bridge.

This paper outlines how innovative construction methodology was included in the design to address construction program issues (bridge construction in one weekend track possession) and tight site constraints at each end of the bridge.