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Precast bridges help to minimise impact on sensitive site

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Rocla® precast components helped Energy Australia renew six creek crossings with minimal disturbance to an environmentally sensitive site at Newcastle.

Kooragang Island, in the mouth of the Hunter River, is best known as one of the largest coal export terminals in the world. However, the island is also part of the Kooragang Nature Reserve, the largest single estuarine reserve in NSW and a wetland mecca for migratory shorebirds.

The island has a large industrial area but also features a diversity of wetland types, including mangroves, saltmarsh, mudflats, sandy beaches and rainforest remnants.

Energy Australia has high voltage overhead conductors running across the island, with access tracks through areas with protected saltmarsh grasses and habitats for threatened species such as the green and golden bell frog.

The access tracks had become unusable for vehicles because of six rotting timber creek crossings, one of which had collapsed in the 2007 storm that ran aground the bulk coal carrier Pasha Bulker.

Contractor ACME Services were successful tenderers for construction of the crossings to the Rocla and Energy Australia design. An original plan to use single span concrete planks to replace the timber pole bridges on all of the affected water crossings was rejected because of restrictions on plant, electrical safety and environmental factors.

In consultation with Energy Australia, ACME Services suggested constructing the bridges from inverted box culverts with lids. These could be installed by a 25-tonne Franna crane, using span-over-span construction, and without leaving the track.

This also obviated the need for concrete footings, minimising disturbance to creek flows, which was a concern for Fisheries NSW. Only one of the crossings could be constructed from concrete planks because of easy site access and existing hardstand areas.

The smallest of the culvert bridges have two bays and the largest three, while the M-Lock® bridge is a single span crossing using 15 metre Rocla M-Lock® precast planks.

Saltwater conditions required special designs for the components.

All products were designed and manufactured to provide for the specified Exposure Classification C and ensure durability and design life were not compromised.