To cope with a rapidly increasing population and to provide an alternative to the congested West Gate Bridge, the West Gate Tunnel is being constructed in Melbourne. The 4.0 km outbound and the 2.8 km inbound twin tunnels will link the West Gate Freeway to a bridge over the Maribyrnong River and an elevated freeway over Footscray Road, which will then connect to the existing CityLink Freeway.

The Northern Portal of the West Gate tunnel is being constructed adjacent to Whitehall Street and will be the launching area for the tunnel boring machines being used to excavate the twin tunnels.

The Northern Portal comprises a cut-and-cover tunnel section approximately 330m in length with an excavation depth that varies from 23m to 5m. The retaining walls in the areas of the deepest excavation consist of 1500mm and 1200mm diameter hard-hard bored secant piles. Bauer proposed hard-hard secant piles, with reinforcement to primary and secondary piles, as an alternative to the conforming hard-soft piles to improve constructability and be more cost effective. The sections requiring intermediate excavation depths use 900mm diameter hard-soft CFA secant piles and the shallow excavation areas adopt sheet piles as the retaining structure.

Bored and CFA foundation piles were installed to support various temporary gantry cranes, TBM assembly frames and excavation strutting and also to provide tension capacity beneath the cut-and-cover base slab. A number of king posts were also required, installed as plunge columns.