The new sewer has enabled the removal of the Kahibah 1 pump station and reduced the wet weather overflow impacts on the environment. The bore was difficult due to site constraints of the state recreation area, limited access to the exit pit and bore line and exacting grade tolerances of -2% with no zero or positive grade allowable. Grade complexity was further compounded by the varying geology comprising of conglomerate sandstone, siltstone, mudstone and a fractured 2.5 metre thick un-worked coal seam intersecting the bore path for 65 metres.
UEA and Bowdens Group worked together to submit design options, a draft proposal and then a final detailed design confirming grade and pipe diameter suitability.
Once the physical constraints were determined, works began to secure approval from the National Parks and Wildlife Service to allow for land clearing for the rig setup and excavation of the 4 metre square x 5 metre deep exit pit. Site preparation works began with the clearing of bushland to allow UEA’s maxi rig spread to be mobilised. Detailed survey works were undertaken to enable accurate tracking of the bore using the Vector Magnetics steering tool. Steering utilised a combination of beacon tracking and Paratrak 2 wire track systems through the dense bushland covering the bore line.
Due to the fractured coal seam and concerns over fluid loss the team back reamed the bore straight to size. PDC reamers enabled steady progression through the varying ground conditions, and a clear distinction between ground conditions was evident when pure black coal chips came off of the shaker screens.
Once the bore hole was complete, conditioned pipe installation began. Due to the limited access to the exit pit, close proximity to Flaggy Creek and being within a popular National Park, pipe installation was undertaken in a weld and push operation.
For more information about this project or UEA Trenchless, please send enquiries to Steven Hopkins.