Don't Tear Down This Wall – Renewal Of A U Shaped Sewer
Annual Conference
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A condition inspection on an ageing trunk main in Porirua identified a high level of microbial induced corrosion on the pipeline with pipe soffit deteriorating and reinforcing exposed.
An options assessment was undertaken to determine the most effective method to renew or replace this 675mm wide x 1000mm high U shaped sewer which runs through a residential area including beneath private properties. The considered options had to minimise any reduction in the capacity of the sewer with a requirement to maintain maximum hydraulic capacity.
Cured in Place Pipe (CIPP) lining was selected as the most suitable methodology for the renewal. Large diameter manholes were installed along the mains to allow access for the structural liner installation.
Issues encountered on site included; a pipe cutter obstruction occurring in small diameter sections of the line, a heavy rain event which consequently caused trench washout and the distinctive odour of styrene through the CIPP curing process.
Installation of the U-shaped main liner resulted in some longitudinal fins and invert wrinkling occurring. The contractor was required to undertake manual entry to remove the majority of the fins. As health and safety holds a vital role within site function, this part of the project required an extensive amount of planning and preparation. The results proved to be successful with majority removal of the fins, however, some invert wrinkling remains. These are currently being monitored to ensure no loss of performance of the pipeline. This experience proved to be beneficial as lessons were learnt and recorded for future large diameter unconventional shape lining projects.
Despite the contingencies that were encountered on site, all parties involved maintained a high level of interaction and communication. Wellington Water, Stantec and Pipeworks ensured the job was completed within the capacity that met budget and customer requirements. The project was completed with minimal inconvenience to the local community and no complaints were recorded.