January 2020 saw two critical sludge pipes lose pressure and fail, forcing Wellington Water (WWL) to transport sludge by truck 24/7 for disposal. Investigations revealed a pipe burst 250m inside the Mt Albert tunnel - a gravity pipe carrying wastewater to the city’s water treatment plant, buried deep under the city’s town belt.

Built to last at least 80 years, WWL did not expect one, let alone two sludge lines to fail. Both ruptured pipes were encased in a concrete surround within a 1.85km long tunnel running from Island Bay to Lyall Bay. To complicate things further, the tunnel had only one access shaft and shutting down the feeding pump station for longer than an hour was impossible. Repairs needed to be done remotely.

WWL engaged Brian Perry Civil (BPC) and Stantec to design a solution. The project team concluded a full pipeline liner was the most appropriate repair method. Two 1.8km liners were procured from Amex Samivar in Germany and installed by Hadlee and Brunton, the longest Amex had ever produced. Working seven days a week during the Covid-19 level 4 lockdown BPC’s crew ensured the site was ready for the liners’ arrival and worked with WWL and H&B for five Amex technicians to come to New Zealand to assist with the install.

On 21st May 2020 the first pipeline was switched back on, with the second pipeline repaired in June. BPC then moved on to the second stage of the project to repair damaged sections of concrete 250m from the tunnel access point. BPC installed communication, over pumping and ventilation systems to provide safe access to the challenging confined space for this work. A comprehensive community engagement programme also saw the project team working closely with residents to address their needs and concerns.

Awards

1. Winner of 2021 Civil Contractors New Zealand (CCNZ) Wairarapa Branch Regional Awards - Winstone Award for projects over $2M
2. Winner of 2021 Civil Contractors New Zealand (CCNZ) Wairarapa Branch Regional Awards - Health and Safety Award
3. Highly Commended 2021: Civil Contractors New Zealand (CCNZ) National Awards - Category 3 $5m to $20m projects