Challenge

The original all-timber Blades Bridge in New South Wales (NSW) was installed in 1916, replaced in the 1950s, and strengthened in the 1990s. However, the bridge has since become severely dilapidated and in 2008 was closed when it was assessed by the University of Technology Sydney as being structurally unsafe.

This presented a considerable inconvenience for local communities with 15kms added to their journeys in and out of the park. Furthermore, the local authority’s attempt to install a replacement bridge was complicated by geological uncertainty from mining activity in the area.

A new bridge would need to cope with longitudinal movement of up to 700mm due to mining subsidence and upsidence.

Solution

A Mabey Compact 200™ (C200™) panel bridge was chosen as a replacement for the 18.3m span over the gorge, not only because of Mabey’s ability to guarantee prompt delivery but also as a result of the performance that the C200™ delivers.

A 4.2m wide single-lane carriageway was chosen as the roadway. Bankseat abutments were keyed into the rock behind the existing timber bridge supports, with one cast in situ and the second precast offline at site and lifted into position with a crane. Illustrating the simplicity of the design, the new panel bridge structural skeleton, formed from 3.048m modules, was assembled into two segments in the works yard by two inexperienced workers in two days using a small crane and hand tools. The bridge segments were then loaded onto trucks and transported to the bridge site.

Result

The replacement Blades Bridge has been a success with the coordinating engineer, Michael Nelson of Wollondilly Shire Council being recognised for his role on the project. He was awarded the Institute of Public Works Engineering Australia (NSW) award for Public Works Leader of the Year.

The new bridge was installed just one year and seven days after the old bridge was closed and will provide many decades of reliable use. Mabey’s innovative, safe and cost-effective solution helped the Wollondilly Shire Council deliver a safe and efficient solution for their citizens.