Bridges

The METRONET Morley-Ellenbrook Line (MEL) Project involved the construction of a 21 km rail line from Bayswater Station to Ellenbrook, in Perth Western Australia. The project required the construction of an 850 m long viaduct to carry the new line over the Midland Down track east of Bayswater Station and local roads to tie in with a dive structure underneath the Tonkin Highway.

The MELConnx Alliance (alliance between the Public Transport Authority of Western Australia and Laing O’Rourke) appointed Design & Analysis and CMW Geosciences to develop the concept and detailed design for the viaduct.

The design provided a unique solution to address site constraints created by the need for large bridge spans to accommodate the new Midland Down track, catering for tight track alignment curvature and acute angled road crossings. By orientating the headstocks longitudinally and creating an integral connection between the superstructure and substructure, the design optimised the use of the maximum beam length currently achievable by the precast yards in Perth and the structure’s interaction with the directly fixed rail.

A monopile substructure solution was developed, whereby each column was supported by a single large diameter pile, eliminating pile caps and improving construction staging close to the operating rail line. An integrated Geotechnical and Structural engineering approach was followed to optimise the response between the piles and the integral bridge structure.

The superstructure design incorporated a bespoke designed precast prestressed box beam with precast transverse slabs forming a through type deck arrangement. This allowed the beams to act as secondary containment for the rail, thereby enhancing safety whilst minimising structural depth.

The modular construction approach enhanced safety, improved the quality of the works and reduced construction duration.

This paper covers the analytical approach, detailed design, material technologies, staging, and modular construction techniques employed to successfully deliver this unique project.