Unity Water Sewer Rising Main Upgrade



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Unity-Water-LogoUEA Trenchless completed a 1.1km design and construct pipebursting upgrade for Unity Water in Deception Bay, Qld. The existing main varied from a combination of 150mm – 200mm Asbestos and PVC pipes that were replaced with 250mm PE PN16. The contract consisted of 2no. connections; one to the stop valve near the pump station at the eastern end of the job and one on the western end of the job into the existing gravity network.

The existing rising main had recently been by-passed as sections had started to deteriorate and collapse requiring full replacement. Unity Water had chosen pipe bursting as the preferred method to replace the defective main for the following of reasons;

  • Close proximity to two schools
  • The main is located under a footpath
  • Close proximity of the main to the root system of a large Moreton Bay Fig tree
  • High pedestrian flow
  • Containment of the existing pipe material
  • Working close to main roads
  • The possibility of working in contaminated or acid sulphate soils
  • The possibility of ground water

Little was known of the exact location and depth of the existing main especially through the park at the eastern end of the job. Due to this, the first stage of the project was to pothole, locate and record the existing main using a vacuum excavation truck.  This information was then used to design the new main. One finding from the investigation was that at tender stage the estimated depth of the existing main was 3m but it was discovered that the main had a depth range of 500mm to 1m. Due to the upsizing aspect of the project, without careful operation and monitoring during the bursting process, major damage could occur to the existing footpath.

Once the design had been approved, the construction began in January 2013. The job was broken into approximately 100m runs, with a pit located at either end for the machine and the other to launch into. The difficulties of this project became apparent with the very first run -minimal cover, the existing main location and material and the proximity to the local school. All of these issues highlighted the benefits of using the pipe bursting technique. Further benefits of the technique became apparent as the project progressed. In particular the fact that the TT Grundoburst 800g pipe bursting machine could be fenced off and isolated whilst still maintaining a safe path for the school children to walk around.

The next problem that had to be controlled was possible damage to the existing footpath caused by heave during the bursting process due to the minimal cover. Advance notice of this issue and good communication meant that the damage could be managed and dealt with swiftly. Poor operation of the equipment could have led to 100% of the route needing to be reinstated but the skilled UEA staff limited this damage to less than 5% of the route – including the launch and receipt pits.

Another issue identified during the construction process was the continual change in the existing pipe material. Mid-way through PVC or asbestos cement pipe sections of DICL were found – particularly at each of the road crossings. To overcome this, specialised tooling was required to be shipped over from Germany. Once this tooling arrived, these sections of pipe were able to be burst and new PE pipe installed.

Once the new PE pipe had been installed all of the connections were completed and the new main pressure tested. Upon successful completion of the testing all restoration was finalised and completed to the satisfaction of the client and local council.

A commissioning plan was then developed and in conjunction was Unity Water and their maintenance crew, the main was then commissioned in May 2013.

For more information about this project or UEA Trenchless, please send enquiries to Steven Hopkins.