Scope of Works
The existing rising main had recently been by-passed as sections had started to deteriorate and collapse requiring full replacement. Unity Water chose pipe bursting as the preferred method to replace the defective main for the following reasons:
- Proximity to two schools – reduce impact on local area
- The main was located under a footpath
- 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, so the first stage of the project was to pothole, locate and record the existing main using vacuum excavation. 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 three metres, but it was discovered that the main had a depth range of 500mm to one metre. 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.
Project works were broken into approximately 100 metre runs, with a pit located at either end for the machine and the other to launch the pipe into. Difficulties were 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 was possible damage to the existing footpath caused by heave during the bursting process due to the minimal cover. Damage was managed and swiftly fixed as UEA provided advance notice of the issue. Poor equipment operation could potentially have led to 100% of the route needing to be reinstated, but UEA’s skilled staff limited this damage to less than 5% of the route, including the launch and receipt pits.
Another issue identified during construction was the continual change in the existing pipe material. Mid-way through, PVC or asbestos cement pipe sections of DICL were found at each of the road crossings, so specialised tooling was shipped from Germany. Once the tooling arrived, these sections of pipe were able to be burst and new PE pipe was installed.
Once the new PE pipe was installed all of the connections were completed and the new main was pressure tested. All restoration was then finalised and completed to the satisfaction of the client and local council. A commissioning plan was then developed and completed in conjunction with Unity Water and their maintenance crew.
For more information about this project or UEA Trenchless, please send enquiries to Steven Hopkins.