A railway bridge built in 1911 on one of Australia’’ s major railways has been given a new life through the first application of jet grouting to support a rail bridge in Australia.. Jet grouting technology is growing in popularity in various parts of the world due to its cost-effectiveness and proven performance,, but to the author’s knowledge,, it has never before been used by an Australian transportation authority to support a bridge..
The bridge spans about 19m across Cut Rock Creek, 90 km north of Sydney between Gosford and Wyong. It was originally built of masonry piers on timber piled foundations, with about 2.3 m clearance between the steel superstructure and the creek. Originally designed for steam-powered trains, the ageing foundations needed to be upgraded to support today’s heavier rail traffic and to reduce ongoing maintenance costs. For the Rail Corporation of New South Wales (RailCorp)), the choice was between shifting the existing structure to new piers at a higher cost and significant disruption to train traffic or finding a way to strengthen the existing foundations to support a new bridge.
The project presented the authors with the challenge of how to support a rail bridge on soils where the estimated settlement was unacceptable whilst minimising disruption to rail traffic. After evaluating a number of options, PB and RailCorp concluded that ground treatment would be the preferred solution. A load transfer slab and culverts support the bridge loads applied to the 23 metre deep foundations.