Bridges

Driven precast concrete piles are the established value for money piling choice for a number of infrastructure projects in Australia. This paper looks at a large-scale application of precast driven concrete piles in a brownfield-site as part of West Gate Tunnel Project in Melbourne. Installation of new concrete driven piles at a close proximity to existing foundations requires a detailed analysis on the impact of the existing structures and a strict construction monitoring during pile installations.

The West Gate Tunnel Project, includes nearly 20km of bridges and elevated structure with a wide variety of structural forms in a challenging brownfields site. The project utilises more than 150 km of driven precast concrete piles throughout its Eastern Zone with viaduct connections to the Port of Melbourne over Footscray Road, City Link and Wurrundjeri Way.

This zone of the project is located over unfavourable ground conditions including up to 40 m of Quaternary Age Yarra Delta deposits including Coode Island Silt (CIS). CIS is a normally to slightly over consolidated deposit and is susceptible to primary consolidation and on-going creep settlements. This settlement causes negative skin friction to occur on the piles. Driving the precast concrete piles through CIS, typically results in some surface heave and lateral displacement. This heave and lateral displacement may have a significant impact on nearby structures and services, however estimating the magnitude of this displacement is complex.

The design challenges discussed in this paper include:

• Induced lateral displacement of previously installed driven piles for the existing City Link Viaduct and other structures.
• Pile design for significant temporary lateral loads and in-service road and rail collision.
• The presence of sulphate reducing bacteria and its impact on design and durability.