Regional Victorian water utility Gippsland Water has been collaborating with contractor Fulton Hogan, and subcontractor Edge Underground on the third and final stage of the $A13 million Warragul Central Trunk Sewer main installation.
Measuring nearly half of the deep-gravity sewer’s total length of 4 km, the $A6.1 million project phase comprises a series of microtunnelling crossings beneath creeks, roads and railways, installing HOBAS-supplied glass reinforced pipe pipelines at depths of 4-7 m below ground level.
Two out of three crossings complete
The third phase of the project requires three critical infrastructure crossings: a crossing of the Gippsland Railway, a crossing beneath the old Princes Highway (Princes Way) and a crossing passing beneath the main Warragul thoroughfare of Howitt Street.
Following careful planning and design, Gippsland Water, in consultation with the local Baw Baw Shire Council identified the sections of the project leg that would require the use of trenchless tunnel boring. Edge Underground then undertook the bores using the Vermeer Axis Guided Boring System, installing HOBAS pipe with diameters ranging between 200-700 mm.
“The crossing of the Gippsland Rail required two years of careful planning and design in consultation with V/Line and VicTrack, with construction successfully completed over two nights without impact to train services,” commented Gippsland Water.
Gippsland Water, Fulton Hogan and subcontractor Edge Underground has wrapped up two of these three critical crossings so far, with the Howitt Street crossing the final operation to be conducted. For the final crossing, a layer of highly weathered basalt rock is expected to be encountered.
Edge Underground Managing Director Stuart Harrison said the ground conditions and a risk of failure were the key reasons for Gippsland Water and consultant GHD to opt for slurry and displacement microtunnelling for the two projects thus far.
“Many challenges had to be overcome in order to deliver a tight tolerance in vastly changing ground conditions,” said Mr Harrison.
“The use of a 350 mm pilot shot as a form of geotechnical sample proved to be a significant factor in delivering a successful project without requiring any additional shafts.”
Warragul on the grow
According to Gippsland Water General Manager of Customer Service and Communications Paul Clark, the third stage of the Warragul Central Trunk Sewer project directly addresses capacity and operational deficiencies in the existing sewerage system while also catering for future growth of the area.
“This investment allows for future development of the Warragul township along with fast-growing areas to the west and south of Warragul,” said Mr Clark. “Previously un-sewered properties close to the Warragul CBD will also be serviced.”
Once operational, the new sewer main will have emergency storage capacity within the pipeline system, allowing Gippsland Water to decommission two existing pump stations currently located on the western edge of Warragul, thus alleviating operational costs and risks.
The overall project is due to be complete and in operation by 30 June 2015.