The benefits of trenchless technology were demonstrated recently when a large section of sewer pipeline collapsed close to homes in Geelong.
A section of Geelong’s trunk sewer main, a 1350mm diameter reinforced concrete pipeline, collapsed after heavy rain following a prolonged period of drought.
Quick work by Barwon Water to clear the blockage, stabilise and cover the hole prevented further damage and stopped raw sewage from overflowing into the nearby Barwon River.
A search then commenced to identify a permanent structural repair for the 160 metre long section of deteriorated sewer. The depth and location of the pipeline meant repairs would need to be made with minimal excavation – preferably none.
In addition, the main could not be taken out of service during repair and total by-pass pumping was not an option. In effect, repairs could only be made at night during an 8-hour period of low flow. Two rising mains from local sewerage pumping stations would continue to discharge into the pipe intermittently.
Any solution had to assume the host pipe was severely deteriorated with no remaining strength.
Barwon Water knew of the Rotaloc system provided in Australia by Melbourne-based Interflow Pty Ltd. The system had been used successfully to line large diameter stormwater pipelines under low flow conditions in Melbourne.
Rotaloc is a spirally wound PVC liner which is installed by a winding machine travelling inside the compromised pipeline. The pipe is not blocked during installation and while flows need to be managed, the pipeline does not need to be taken out of service.
Inspection of the pipeline at Geelong by Interflow confirmed structural lining with the Rotaloc system under the conditions required by the project was possible. Based on the assumption the pipeline had no remaining strength, Interflow proposed using a liner capable of taking all applied loads.
The first challenge to face Interflow was the removal of debris. More than 40 cubic metres of silt had washed in and in some places silt filled the pipeline to 40 per cent of its diameter. Following the successful removal of the debris, on 7 March 2002, installation of the liner in the 1350mm pipeline began.
Services to Barwon Water customers were maintained throughout the project. All work was carried out after 10pm during periods of low flow. Each night, winding of the liner would cease while pump stations operated to relieve upstream storage capacity and until the flow subsided.
Installation of Rotaloc does not block a pipeline, no heating is involved and there is no need to remove winding machinery or take special precautions to protect the newly installed liner during increased flow conditions.
After the lining was installed cementitious grout was injected into voids external to the host pipe and around the new liner.
The project was completed on March 20. The damaged sewer was successfully repaired with minimal inconvenience to the community.
By John Monro.