Bridges

The Westconnex M4-M5 Link Tunnels project is the third stage of the Westconnex program of works in Sydney. The project links the southwestern M5 to Western M4, passing through St Peters Interchange, the most complex interchange in Sydney to date. Included in the works at that interchange is a motorway operations facility consisting of a ventilation building, electrical substation and other services contributing to the seamless operation of the motorway. The ventilation building is situated above the tunnel entry and exit portals and is supported by the St Peters Interchange Ventilation Building Cut and Cover structure.

This paper covers the complexities in design and construction of the cut and cover structure. The structure is unique, utilising Super-T girders that are fully integral with the substructure across multiple spans. The structural form was influenced by several key constraints. The position of the tunnel ventilation outlets was predetermined to be above the tunnel portals, dictating the need for the ventilation building to be supported above the tunnel carriageways. The layout of the building and potential irregular movement joints was also a key consideration and was further complicated by the carriageway road alignment and the interface with adjacent structures.

The constraints resulted in the decision to utilise a fully integral connection between superstructure and substructure. This allowed many benefits to the design, construction, and future maintenance of the structure. The continuity of the structure enabled the design of the Super-T girders and piles to be optimised and removed the requirement for bearing inspection and replacement. This is noted as a key benefit as jacking of the structure would have proved practically impossible. This paper will discuss the various constraints and benefits, the analysis and modelling techniques used in design, and the detailing challenges and opportunities of integral cut and cover structures.