The manhole nearest the problem section receives sewage from a rising main and discharges it into a gravity section. The concrete pipe adjacent to the maintenance hole to corrode, allowing soil to leak into the pipeline, so creating the hole.

The first task for Interflow was to divert flow around the damaged section.

Upstream of the maintenance hole the pipeline had been constructed in a tunnel that passed under the Freeway. Interflow, with Sydney Water’s assistance, cut into this pipeline, installed a tee piece and valves and connected it to a large bypass system. Twin 300mm diameter polyethylene pipelines were laid above ground to carry the flow to a maintenance hole downstream of the works.

The next task was to construct an 8 metre deep shaft at the location of the sink hole. Ground conditions meant that extensive timber shoring of the shaft was needed. From here the project required Interflow to install Expanda Pipe liners in two 600mm diameter lengths of pipeline – 90 metres and 166 metres long. The depth of the pipeline and its location meant that excavating and constructing an intermediate maintenance hole wasn’t feasible.

Lining 166m of 600 diameter pipeline with 126Ex20 in one operation meant installing the heaviest Expanda Pipe liner in Interflow’s history. It wasn’t the longest. But 166 metres of 126Ex20 is the heaviest liner we’ve had turning at once – over 2.3 tonnes.

After all preparations had been made, winding and expanding of the liner was completed in one shift

It was a project to be proud of. Successful completion meant overcoming lots of construction and safety challenges – a deep badly deteriorated pipeline, highly toxic sewage, close to a freeway and of course the long distance between maintenance holes.

At the conclusion of the project Interflow received a letter of appreciation from Sydney Water’s Area Manager. It read in part “your quick response, site management skills and cooperative approach enabled us to manage such a high risk and large incident minimising environmental impacts and protecting public safety.”