Bridges

The West Gate Tunnel Project involves the construction of twin tunnels under Yarraville to provide an alternative route to the West Gate Bridge. A major bridge over the Maribyrnong River connects the tunnels to a new elevated viaduct structure over Footscray Road. Another two multi-span bridges over the Maribyrnong River provide entry and exit ramp connections from the tunnels to the Port of Melbourne.

The structural solution for the entry and exit ramp bridges over the Maribyrnong River was largely driven by the substantial geometrical constraints. These constraints included the proximity of the tunnel entrance/exit to the western bank of the river, the requirement for the bridges to provide sufficient clearance over the river to preserve the navigation channel, and the need for the bridges to connect to Mackenzie Road immediately on the eastern riverbank, all while not exceeding maximum road grade requirements. This resulted in both bridge alignments having a tight horizontal radius of approximately 100 m.

To best achieve these geometrical requirements, the entry and exit ramp bridges consist of three continuous spans of large, curved steel box through girders spanning from the western bank over the river with steel transverse-girders secured to the bottom of the through girders. The transverse girders are compositely connected to the concrete deck slab. Additionally, the exit ramp has seven approach spans on the western bank consisting of prestressed concrete planks and Super-T beams with composite concrete decks.

This paper covers the design approach and construction stage related aspects of the curved steel box through girder spans of the two bridges. The paper highlights the determined structural behaviour of the bridges, the adopted connection details, and the development of the staged construction requirements.