Laidley Timber Bridge Replacements

Contract Value: $3.4M

The project consisted of a design and construct contract to replace three existing timber rail bridges with two reinforced concrete culvert structures and a section of earth embankment rail formation. The purpose of the project was to replace the high maintenance timber bridges for Queensland Rail while also increasing the hydraulic efficiency and flood immunity in the area. 

The project was a design and construct project with the new structures designed to be ballasted track to Queensland Rails QR-300A loading criteria. Existing rail levels were to be maintained and the flood efficiency of the structure was increased by 30%. The project was designed by KBR, with site construction supervision provided by Queensland Rail. 

The replacement structures were constructed during three 48 hour full track closures with services restored prior to the end of each 48 hour window. The works carried out in each closure included demolition of the existing structures, subgrade improvement, installation of new structures, approach earthworks and track reinstatement work. The section of line in which the replacements occurred is dual track, servicing freight trains including coal and cattle as well as long distance passenger services. This meant that any issues during construction would have major consequences for several stakeholders. 

Key features of this project include:

  • Demolished structures were predominately timber and up to 34.2m long. One bridge structure was concrete with steel girders 
  • Subgrade improvement works required beneath culvert base slabs; approximately 600m3 of in-situ material removed and replaced with rock and road base during each 48 hour closure. 
  • Rail formation built either side of the new structures, as well as in area where the concrete and steel bridge was removed
  • Two culvert structures constructed, consisted on precast base slabs with reinforced precast box culverts. One bridge was 22no. precast base slabs and 140no. 1.2m high culvert unit. Base slabs were designed to be 7 culvert cells wide to allow for efficient placement during closure weekends. 
  • All precast items installed during the three 48 hour track closures. 
  • Structures were designed to remove most construction works from rail corridor prior to shutdown periods, thus eliminating majority of the risk to both rail traffic and the construction team
  • Works carried out during closures were completed successfully within allotted time frames with no delays to the rail network.