Signature Project

The New Hospital Bridge in Mackay

A $26.7 million project for the construction of new two bridges and extensive road works for the Department of Main Roads in Mackay.

Work on the project commenced in September 2007 and was completed in April 2009.

The smaller of the two bridges has two spans with a deck consisting of transverse post stressed deck units and an asphalt wearing surface and provides access over the Lagoon Creek, which feeds into the Pioneer River.

The main bridge, which crosses the tidal Pioneer River upstream of the existing and regularly flooded low level Hospital Bridge, has twenty two spans, each 25m long and 11.9m wide.

The bridge deck on the main bridge consists of super T concrete girders, with in-situ cast concrete deck slabs and up-stand kerb walls.

With thirteen of the twenty one piers being located within the Pioneer River, the window of opportunity for construction of this section of the bridge was limited to the “dry” season, from March 2008 to November 2008.

Planning of the construction sequence had to take these local conditions into account and endeavour to have as much as possible of the “dry land” works complete prior to the commencement of the works in the river.

Construction work in the river was undertaken from a platform of river sand that was built out into the river to an elevation that was above the expected highest tide level that would occur. In order for the normal ebb and flow of the river not to be significantly affected, the platform could not extend across more than half of the river width at any time. This restriction meant that the sand in the platform had to be relocated by leapfrogging it across to the other side of the river for the second half of the works in the river to be completed.

Each of the piers was supported on three 1,5 m diameter piles, up to 28m in depth and with sockets into the bedrock that were in excess of 6m deep in places.

A number of the pile sockets were in rock that was too hard to remove using conventional piling equipment and the slow process of cluster hammer drilling was utilised. The cluster hammer is a multiple head pneumatic auger suspended from a traditional drill rig Kelly bar and is a new innovation to Australia, imported from the USA.

This process caused significant mid program delays to the project and created some anxiety regarding whether the foundation works would be complete prior to the onset of the 0809 summer rains.

Fortunately the rains came later than expected, the temporary works in the river were not damaged and the overall completion of the bridge and roadwork was achieved without significant delays being incurred.