The main gravity sewer supply line to the Moa Point Wastewater Treatment Plant in Wellington travels via a 1.8km concrete lined interceptor tunnel that stretches from Island Bay to Kilbirnie. Cast in the concrete base of the tunnel are two 1.8km, PN35, DN150, concrete lined ductile iron pipes. These pipes allow the untreatable sludge from Moa Point to be pumped back to the landfill in Happy Valley. Due to a seismic event towards the end of 2019, it was discovered that the concrete tunnel benching had lifted and broken approx. 250m down the tunnel. Both pressure pipelines had also broken and were pumping sludge into the interceptor tunnel. Neither of the sludge pipelines could be used forcing Wellington Water to run a fleet of vacuum trucks 24 hours a day, 7 days a week to transport the sludge at a cost to ratepayers of over $600,000.00 per week.
The main issues faced by Wellington Water were:
There were no pipe cameras in the world that could reach the distances required in such a small diameter pipe. Therefore, H&B and our camera specialist designed and constructed a camera that was able to give a full live stream of the pipeline, 3D scan and measure the damage to 0.01mm accuracy. This was the first of its kind in the world. After obtaining the footage of both pipelines and determining that the Amex pressure liner could be used, the pipelines had to be flushed, pigged and cleaned to enable us to install the mechanical couplers over the sections of pipe that were broken. This was a very technical procedure since the installation of the couplers were approximately 250 meters into the pipeline and they had to be installed with great precision to ensure adequate coverage of the breakage was achieved. With the successful installation of the couplers then the final cleaning could be undertaken followed by the lining works which occurred over two days. Destructive tests of the liner and couplers achieved a PN75 burst rating this excluded the steel host pipe.
It was the first time the Amex pressure liner had been used in the Southern Hemisphere and it was a world record installation length. To make the contract works even more challenging, we had to procure and complete the work in the middle of the global pandemic of COVID-19 and our national Level 4 lockdown. Due to the critical and urgent nature of the works, this was signed off by the Prime Minister of New Zealand as an essential job that had to commence even though the entire country was locked down. We were the first company in NZ to be allowed to fly essential workers into the country under the state of emergency and also had to find a way, with the help of the NZ and German governments, of flying a liner this large into NZ with all international travel grounded or severely reduced.
Hadlee & Brunton Ltd
6 North Street, Timaru
(03) 684 3817
plumbers@hadleeandbrunton.co.nz