Hamilton City Council’s $7.65 million wastewater project in Rotokauri – vital to unlocking growth in the area – is nearing completion.
The Far Western Interceptor Extension extends the city’s current wastewater network with a two‑kilometre pipeline from the Te Rapa bypass to the existing pipeline beside Avalon Drive.
Rotokauri has been identified as key for future growth on the perimeter of Hamilton, with about 1000 hectares identified for residential, commercial and industrial expansion.
Up to 20,000 new residents are expected to move into the area over the next three decades.
Hamilton city council awarded West Construction this project and Humes was made the exclusive supplier for concrete products. Due to the large nature of the project, Humes and West developed a partnership approach to the job. Heath Rickit, civil engineer at West Construction says; “The project was originally going to start with a 450-capacity pipe which would have been large enough as it was going to be sufficient to take over the excess wastewater of the Western Interceptor, but the Council decided to upgrade to a larger diameter pipe (DN1050), which is actually a lot easier to work with.”
Hundreds of pipes and two manholes were first delivered to site. The project required 860 DN1050 class 4 Polyethylene (PE) lined pipes, and 14 DN1800 PE lined manholes.
Stan Hodson, account manager at Humes, says the biggest challenge Humes faced was the ground condition and the timing for the project.
“The Council had put a tight deadline, and we had to match our production schedule to the required contractual time frame.”
The project window meant Humes had to produce a minimum of 15 pipes per day. The manholes and cover lids are also all PE lined, so Humes used a different manufacturing process for this as it is not standard.
“About 300 pipes and two manholes were first delivered to the site, and then we based our production schedule around their lay schedule,” says Hodson.
“It gave us credibility in the marketplace to be able to deliver a large volume of concrete pipes and manholes to the technical specifications of the Council and the contractual requirement the contractor had to meet within the deadline.
“We believe Humes’ manufacturing process is the only process in the country capable of delivering large volumes of concrete pipes and manholes within such a tight timeframe.
“Like any project, until the contractor had started digging, we had no idea what the ground condition would be like. So once they started laying, they were able to give us their lay schedule.”
Another challenge was welding the pipes to match QA requirement from the council. The PE liners were welded in all-weather and ground conditions, section by section to avoid contamination of the liner.
“Humes has a full 360 degree AGRU PE liner, and to be honest, it is much easier to weld,” says Heath.
“We also found the PE 80 AGRU liner a lot easier to work with because it’s softer and therefore it’s much more malleable.”
The pipeline is future proofed as it allows for population growth and being PE lined, there will be no hydrogen sulphide degradation, therefore extending the asset life.
Due to hydrogen sulphide issues in New Zealand, Stan believes PE-lined concrete pipes will become more widely used.
Moreover, as shields for pipe installations in deep ground conditions are required, Humes’ 2.5 metre long pipes are embedded in the shields, making it a safe environment for contractor staff to install.
“Humes West partnership have delivered the council a very successful outcome. There will be more stages in the council growth plan, so this is a pretty critical project that will improve the city network,” says Stan.