Bridges

In November 2015, the Sydney Motorway Corporation awarded the Leighton Dragados Samsung Joint Venture the contract for the design and construction of Stage 2 ñ New M5 (Now M8) of the WestConnex project. The M8 runs from the existing M5 East corridor at Beverly Hills via a tunnel to an interchange at St Peters. The detailed design was completed by the Aurecon Jacobs Joint Venture with involvement from Tony Gee. The interchange was constructed over the top an old brick pit that was subsequently used as a land fill.

It consists of three levels of nine continuous single celled post tensioned box girder bridges above the piled pavement structure at ground level. The bridges were constructed using precast segments erected using balanced cantilever and on-staging methods of construction. Piled foundation design and construction techniques accounted for piles progressing through landfill of unknown make-up as well as suspected steep inclined rock faces near the perimeter of the pit. Balanced cantilever construction required superstructure restraint either off the top of piers or in the case of single bearing supports, off temporary steel support frames.

The design of the post-tensioning tendons that tie precast concrete segments permanently together joints are critical for the design of the bridges. The effectiveness of the tendons does not only impact on the direct cost but also time to construct. It was a challenge to design the tendons for the different bridge geometries and span configurations to ensure the strength and serviceability criteria were met at each stage of construction and during the bridges service life. The paper covers the method of analysis, detailed design of post-tensioning, other specific design and construction considerations for effective delivery using the match-cast segmental balanced cantilever method.