Customer: Auckland Council
Location: Papakura, South Auckland, New Zealand
Budget: $19 million NZ
This stormwater upgrade is 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 involves 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 will be 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 will complete the four drives (MTBM) required for the project, which is the largest trenchless project to be undertaken by Auckland Council for some time.
The project involves work in McLennan Park and Katavic Park, and park access and walkways have remained open during construction requiring stringent safety and environmental management. Groundwater discharge and monitoring is the most significant consent compliance requirement. We have encountered greater than expected levels of groundwater on-site, which has 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 range from 6 m to 13 m deep.
KEY TO SUCCESS
Despite the unforeseen ground conditions, the project is 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 have also implemented control plans and allocated people to ensure compliance across quality, safety, and environmental aspects, and are delivering to the Council and our own high standards.