Case Awards are open to all fields of civil engineering. Interflow were winners this year in the ‘Up to $A5 million’ category for a project to structurally restore a deteriorated 1,800 mm nominal diameter sewer pipeline for Sydney Water. This followed on from the 2004 National Award for lining of a 900 mm diameter sewer using Rotaloc.

The 2006 project, ‘Rehabilitation of the Coogee Diversion Sewer’ saw the world’s first use of Ribline, a large diameter spirally wound steel reinforced polyethylene liner, developed in Australia by Rib Loc in conjunction with Interflow. In making the Award, the judges’ endorsement stated: “The process and construction techniques developed by Interflow will set the standard for industry best practice in future large diameter sewer rehabilitation jobs.”

“Innovation and continuous improvement have always been part of our company’s culture,” said Interflow Managing Director Geoff Weaver. “To win this Award twice against such wide ranging competition is a credit to the ingenuity and experience of our people. The fact that we won it on the day of our 70th anniversary was an exciting coincidence.”

The project involved 1.3 km of 1,800 mm diameter sewer up to 7 m deep in a beachside suburb. It required a high stiffness liner to be installed with minimal excavation while the sewer remained in service.

Ribline is a further development of Rib Loc stormwater pipe. It is made from ribbed polyethylene profile with a continuous strip of steel embedded in each rib. The steel reinforcement allows a high stiffness liner to be provided in large diameters.

Installation requires a winding machine to be placed in the base of an existing access chamber. From above ground a continuous strip of polyethylene/steel profile strip is fed to the winding machine. Unlike sliplining, excavation of large launch pits is not needed. The profile strip is delivered and stored on site on spools, minimising the size of the above ground worksite.

The winding machine helically winds the strip, welding the edges together to form the liner. Once welded, the liner cannot be expanded so, unlike other Rib Loc lining processes, it has a fixed diameter and thus an annulus between it and the host pipe.

To enable installation with the sewer still in service, Interflow set up an extensive overpumping system to take the non-peak dry weather flow around the section of pipeline undergoing rehabilitation. The system allowed full flow capacity to be quickly restored at peak flow times or in the event of sudden rainfall. Ribline allows this possibility because it does not block the pipeline and, as no heating or curing is involved, flow through a partially installed liner has no detrimental effect on its integrity.

The liner was installed during non-peak flow periods with the flow controlled to allow a depth of about 300 mm of water in the pipeline invert. The liner was allowed to float as it was being wound, minimising friction and allowing long continuous lengths to be installed. After installation the annulus between the liner and the host pipe was grouted.

Successful installation required careful coordination with Sydney Water’s operations personnel and management to ensure on-site safety in difficult underground conditions. Above ground, community liaison was important in completing the job with minimal inconvenience to day-to-day activities.

The project demonstrated another Australian developed advance in Trenchless Technology that delivered a practical solution for a deteriorating vital asset, and the Award highlights the fact that the benefits of Trenchless Technology are receiving prominent recognition from the wider engineering community.