18 May 2012
Hunter Expressway alliance fills the void
The Hunter Expressway alliance has achieved another major milestone with the completion of work to fill mine voids on the eastern section of the project.
Tony Gant, Senior Project Manager for Roads and Maritime Services said the work was extremely important for the Hunter Expressway and the alliance had overcome a number of technical and environmental challenges during the mine void work.
“The work took 15 months to complete and involved a team of 60 people drilling more than 1,500 holes,” Mr Gant said.
“These holes measured a total distance of 145 kilometres and were drilled into the old mine workings, 80 to 120 metres beneath the ground. About 200,000 cubic metres of grout was pumped into the mine voids left by past coal mining activity which dates back almost a century.
“The grout is a mixture of flyash, water and cement with the flyash being a by-product of the power generation industry.
“The work will limit future mine subsidence under the three high bridges through Sugarloaf Range and the F3 interchange bridges.
“The project team carried out extensive investigations to identify and determine the size of the mine voids before filling them to provide a solid foundation for the bridges.
“The final stage of work involved the team reviewing all the old mine records and using a down-hole camera to monitor the condition of the mine. Extra core samples were also drilled to verify the work.
“The major challenges for the mine fill team included the steep terrain in Sugarloaf Range where the drilling sites were located, the risk of mine gases escaping through drill holes and the delivery of grout.
“Directional drilling was used to overcome the challenges of the tight environmental clearing limits and steep terrain. Where possible the mine platforms were built on the permanent footprint of the Hunter Expressway project to minimise the area of land used.
“One of the innovations implemented by the alliance was an 800 metre pipeline which delivered grout from the batch plant to fill the mine voids.
“The temporary pipeline was designed to minimise environmental impact and was laid across the ground using tyres and star pickets.
“The site team did safety training tailored to the specialised nature of the work, including gas awareness training delivered by the local Mines Rescue organisation and a specialised mine fill induction.
“With the completion of mine filling work, progress on the Hunter Expressway is continuing with the building of the high bridges in the Sugarloaf Range and the F3 interchange bridges well under way,” Mr Gant said.
The $1.7 billion Hunter Expressway project is jointly funded, with the Federal Government providing $1.5 billion and the NSW Government contributing up to $200 million.
The Hunter Expressway alliance is building the 13 kilometre eastern section of the Hunter Expressway, from the F3 Freeway to Kurri Kurri. Thiess, as part of the alliance, joined with Keller Mine Fill JV in a sub-alliance to carry out the mine filling.