2102 Monash to Eaton River Crossing
Project Summary
Bunbury, WA
Trenchless Technology
Water Corporation
- Completed
July 2015
August 2015
Project Overview
This 310 metre crossing of DN450 PE pipe is one of many large scale HDD crossings that DM Civil has successfully completed for the Water Corporation in recent years.
An 18 kilometre pipeline was to be constructed to redirect flows from the Monash Boulevard wastewater pumping station (WWPS) and the Kemerton wastewater treatment plant (WWTP) to the South Bunbury WWTP.
DM Civil was awarded the contract for the trenchless sections of the works. In addition, DM Civil was awarded a contract by Construction Branch to install a 310 metre section of pipe under the Preston River, Picton. To install the 310 metres of DN450 PE pipe under the river, horizontal directional drilling (HDD) was the preferred methodology as it allowed for the installation to be completed in a single pipe length. The scope of works included the design documentation and preparation of the drill shot profile and pull back calculations.
The pullback designer’s recommendations highlighted the need to partially fill the main with water during the pullback operation. This was to counteract the effects of buoyancy of the pipe given that the apex of the curvature in the pipe string was approximately 9 metres below the river bed. This was an emerging technique used in the industry to minimise pullback stresses in wet ground conditions and to significantly reduce the force required to install the pipe.
The 310 metre alignment was navigated utilising HDD technology with minimal impact to the surrounding environment and river. This saved the established vegetation and minimised disturbance of a significant Aboriginal heritage site as well as acid sulphate soil treatment.
Significant achievements and benefits
The cavernous limestone ground conditions and water charged ground required specialised trenchless technology equipment. We used our microtunneling machines with Rockman head to ensure each drill shot would be to the required accuracy specified by the client.
Trenchless technology drastically reduced the amount of dewatering required, which in turn allowed for Department of Water clearance for the project to proceed.
The sewer alignment was in the middle of Fawcett Road, with homes on both sides of the road. If this project was constructed using open cut excavation, deep trenching up to a depth of 11m would have been necessary. However, the use of microtunneling eliminated any residential access issues along the route.
The microtunneled pipe was launched inside 4.6m diameter sealed, reinforced concrete caisson thrust and receival pits, up to 11m deep. The sacrificial caissons were constructed insitu so that access chambers could be constructed inside once microtunneling was complete. This method mitigated the risk of settlement around the caisson.
In total, 515m of DN150 and 294m of DN225 sewer was constructed with microtunneling. This was constructed in cavernous limestone ground conditions with the majority below the water table. By using the sealed concrete caisson thrust pits, the dewatering requirements were kept to an absolute minimum. This limited the environmental impacts of the project when compared to traditional open excavation.
By offering trenchless techniques for the deep sewer installation, the client was able to achieve project approvals and minimise environmental impact along the sensitive construction corridor. Residential access was also maintained.
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