Orakei Main Sewer Rehabilitation

Abstract

The Orakei Main Sewer, varying in size from 525mm circular to 2.4m x 1.5m egg shape, was originally constructed in 1910, and runs from Avondale, via Herne Bay and onwards to Hobson Bay, a total of over 8 km. A 250m section of egg shaped concrete block construction 2.4m x 1.5m runs under the Stanley St motorway on ramp, through the Auckland Domain, and under the ASB tennis centre. Until the Central Interceptor comes on stream, starting in the mid 2020s, this sewer will continue to be a critical and essential component of Auckland’s sewer network. Following extensive investigation, it was found that the structural integrity of the crown arch had become compromised due to biogenic corrosion and root intrusion, and that it had reached a level where structural repairs could not be deferred without incurring unacceptable risk. After design and tendering, a project was undertaken to install 150m of glass reinforced lining segments and a further 100m of CAC mortar lining where the condition of the main sewer was of greatest concern. To carry out the lining works, a temporary pump station and rising main were built, to divert flows of up to 800 l/sec. This 12 month project was successfully completed without incident in July 2014.