Hume Highway, Emergency Stormwater Repair

NSW Roads & Traffic Authority Emergency Storm Water Repair Hume Highway

Client: NSW Roads & Traffic Authority (RTA)
Project: Repair of storm water asset within median strip of the Hume Highway, Gilead

The Roads & Traffic Authority is a state government body that builds and maintains roads and other associated assets such as stormwater. Based on our track record, the RTA originally contacted Downer PipeTech to discuss the repair of one of its stormwater assets through pipebursting or directional drilling. As the pipes had dropped and the chamber had collapsed this was soon found to be impossible. Despite the fact that the fi nal solution was purely an open cut one, the RTA still enlisted Downer PipeTech to undertake the management of the design and construction of the project.

Downer PipeTech provides a broad range of world’s best practice technologies for the installation and renovation of pipelines and structures. Our diverse range of trenchless technologies are suited to pressure and non pressure applications, including potable water pipelines, sewer mains and storm water infrastructure Besides the works for the RTA, Downer PipeTech also provides dig and repair services to Sydney Water in their sewer network.

Plans of the existing system showed the stormwater pipes at a depth of approximately 5m. At this depth it was possible to install shoring boxes and repair the system fairly readily. Once Downer PipeTech was on site, however, it became apparent that the depth to the top of the pipes was approximately 9m on the eastern side and 10.5m on the western side meaning an excavation of approximately 12.5m was required. This information meant that the whole project had to be re-evaluated particularly from a risk management perspective. Downer PipeTech was awarded the project in June 2007.

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Project Profile

RTA Storm Water Repair Hume Highway, Gilead

This project involved the emergency repair of the RTA’s storm water asset (two 1500mm concrete pipes) within the median strip of the Hume Highway at Gilead.

Downer PipeTech was engaged to undertake the necessary repair work to restore the structural integrity of the damaged pipes and to prevent further ingress of the surrounding ground into the pipes. The scope of works included:

  • Perform test pile and geotechnical investigation;
  • Design and install shoring system (piles, steel and anchors);
  • Repair collapsed storm water system;
  • Design and Construct new in situ storm water chamber; and
  • Reinstatement of median strip

With the excavation positioned within 1m of the asphalt surface of the Hume Highway, the lateral loadings were signifi cantly higher on one side of the shored excavation than the others. This in turn required 50T SWL temporary soil anchors to secure the excavation back on that one side minimising the risk of damage to the road if lateral movement occurred.

Once the excavation reached a depth where a conventional 30T Excavator was no longer effective, a ‘long-reach’ excavator was fl oated to site. This, however, posed a new set of issues as the length of boom meant the operator needed to position the machine 10m back from the edge of the excavation. This meant a spotter had to guide the machine operator at all times. When the excavation reached a depth of 9m, the ‘long-reach’ could no longer be used as the boom was actually striking the shoring sheets. From this point, a 5T excavator was lowered into the excavation and used to load a bin with spoil before craning the material out. In summary, the space requirement of a 7m x 7m excavation placed a signifi cant limitation on the machinery that could be used.

Once the required 12.5m excavation depth was reached, the fi ll material was found to be unsuitable to bed pipes on; a blinding slab was constructed prior to re-installing the pipe work to provide the necessary structural support.

Project Sheet