When rehabilitating a large diameter sewer, maintaining services to an authority’s customers is one of the difficulties that must be addressed. A rehabilitation system that can be rapidly installed is an obvious advantage.
For SA Water, a 900 mm diameter sewer in Morphett Vale was known to be in need of renewal. In 2004, a 12 metre long section had collapsed and was rapidly replaced with cement lined steel pipe that United Water had available.
But as the whole 120 metre length of the pipeline needed rehabilitation, SA Water’s principal contractor United Water included it along with smaller diameter pipelines in a lining contract awarded to Interflow. The diameter meant that a Rotaloc liner was required. Rotaloc provides a structural liner, effectively renewing deteriorated pipelines, in sizes 900 mm and larger.
As the 900 mm diameter pipeline carries high flow at all hours, before any work could commence, a flow bypass system was installed. Three 200 mm pumps, two of which were on duty with one on standby, pumped about 200 litres of flow around the section to be lined. Interflow and United Water worked together to identify and then reduce all the risks associated with such a large pumping operation, including the development of contingency plans to be applied in the unlikely event of the worst case scenarios arising.
Article continues below…Once the bypass had been trialled and was operational, CCTV inspection was undertaken. It showed that deterioration had been rapid and a section of line about 10 metres long was in a condition where any disturbance was likely to bring about collapse. Parts of the pipe wall above the water line had corroded away, allowing the top of the pipeline to move downwards so that it was no longer circular. The only option was to excavate this short section. Fortunately it was located below a park.
United Water organised for a local contractor to do the excavation. Once they reached the level of the pipeline, the top of each deteriorated pipe could simply be lifted off. All that remained was the dished invert and the thicker collars of each pipe.
It was decided that the collars should be left in position so that the smooth inverts necessary to guide the Rotaloc machine would not be damaged.
Excavation took from midday until 8 pm. Interflow’s Rotaloc crew then moved in and had the 120 metre section lined by 6 am the next morning. Flow was immediately restored and the liner in the excavated section of the pipeline was concrete encased.
The entire job was completed within a 24 hour period with minimal disruption to the community. It was an impressive example of the benefits of Trenchless Technology.
