The rehabilitation of deep sewer mains, near Australia’s Parliament House in Canberra, was an Australian first. The sewer rehabilitation contract, awarded to Insituform Pacific, involved the rehabilitation of various 450 mm and 750 mm sewers, as well as maintenance hole (MH) rehabilitation. However, it was the 750 mm sewers that presented the greatest challenge to the contractor.
The lines were suffering from hydrogen sulphide gas attack with depths up to 11.4m so a strict design specification was put forward by the client due to the implications of failure. These implications were made worse by the location of the pipe along one of Canberra’s most important roads, Commonwealth Avenue, leading from the city centre to Parliament House. The pipe was also adjacent to the National Library and Lake Burley Griffin, so failure would have led to contamination of one of Australia’s most famous landmarks and the Molonglo River.
Green CIPP installation
Insituform Pacific explored the use of its standard CIPP liner for this pipe, which resulted in the need for a 28.5 mm liner thickness. While it was feasible to install this liner, the significant thickness meant that water inversion and hot water curing would be required for installation. Insituform installs the majority of its CIPP liners using air inversion and steam curing, which is a more efficient and environmentally friendly installation method.
The contractor then explored the use of its next generation iPlus Composite㢠liner, a CIPP lining system reinforced with carbon fibre and/or corrosion resistant fibreglass materials. Only fibres that are resistant to the corrosive environment found in sewers are used. Carbon and Advantex㢠fibreglass materials have excellent chemical resistance to materials found in sewers and exceed trenchless industry corrosion requirements. The product won the 2007 Innovative Product Award in the category of rehabilitation at the 2007 North American Annual No-Dig Conference. Insituform was chosen as the winner over more than twelve submissions.
By using dual layers of high strength carbon fibre reinforcement, the engineers were able to reduce the liner design wall thickness to 15.5 mm, making it suitable for air inversion and steam curing. While the product had not previously been used in Australia, the client and its consultants were confident in the performance of the product following over five years of track record in Europe and the United States.
Engineering success
The iplus Composite laminate design theory optimally locates the structural reinforcing materials, reducing the pipe wall thickness by up to 50 per cent from a conventional CIPP liner. As with other pipe rehabilitation products, the applied pipe loads are calculated according to accepted industry standards, such as AS/NZS2566.1.
The lining work was successfully completed within the space of a week with the longest single installation being 150 m. All lining works were completed without modification to existing MHs, and most importantly, without the need for personnel to be in the MHs or lines during the lining works. The final result was a fully structural, joint-less, tight fit CIPP liner with an incredibly smooth internal surface and a diameter loss of just four per cent.
This project was another example of what is possible when an innovative contractor and a forward thinking client come together to produce excellent results.