Customer: Auckland Council
Location: Papakura, South Auckland, New Zealand
This stormwater upgrade was designed to meet a growing population and expanding city boundary in South Auckland, reduce flood risk in the area and connect the McLennan Park Stormwater Ponds with the Pahurehure Outlet. The work involved constructing five deep manholes, including inlet and outlet structures and prefabricated bends.
Nearly all of the 1.1 km-long, 2.5 m dia stormwater pipe was installed using trenchless technology with a closed-face slurry Micro Tunnel Boring Machine (MTBM), except for a short section constructed using open cut methods. The MTBM completed the four drives (MTBM) required for the project, which was the largest trenchless project to be undertaken by Auckland Council for some time.
The project involved work in McLennan Park and Katavic Park, and park access and walkways remained open during construction requiring stringent safety and environmental management. Groundwater discharge and monitoring was the most significant consent compliance requirement. We encountered greater than expected levels of groundwater on-site, which required a change in methodology for shaft construction.
The original scope of works was to construct five shafts and pipe jack between them approximately 15 m beneath the surface to reduce any impact on the industrial/residential area. Due to the high level of groundwater, we adapted this method for shafts four and five, instead using a secant piling method with augured piles. The five shafts ranged from 6 m to 13 m deep.
Key to Success
Despite the unforeseen ground conditions, the project remained on track thanks to having the right machine for the highly variable ground conditions and an in-house design team able to quickly adapt designs to suit the conditions encountered on-site. We also implemented control plans and allocated people to ensure compliance across quality, safety, and environmental aspects, and ensure we delivered what we promised to the Council and our own high standards.