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Customer: Watercare Services Ltd Contract type: Design and Construct Location: Glen Eden, Auckland, New Zealand   |
Fast Facts
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We upgraded Glen Eden's wastewater infrastructure, using some innovative construction methods to reduce our footprint and lessen the impact on residents. The network upgrades have reduced the number of overflows that occurred following prolonged heavy rains.
The centrepiece of the project was the design and construction of a 2 million litre storage tank under an existing carpark and playing fields in Harold Moody Reserve.
Measuring 20 m deep and 13 m diameter, the original tender design for the tank was for open excavation, constructing it from the bottom up and backfilling the completed structure.
Minimising disruption to residents and the general public was a key driver, so we proposed and adopted an alternative ‘caisson’ approach - significantly reducing the working space required and minimising risk and cost for our customer.
The ‘caisson’ solution is rarely used in New Zealand but more common in large European cities where space is at a premium.
The construction method involved the installation of a steel cutting ring at the base of the walls, followed by the subsequent casting of three 400 mm, 18.5 m in dia, 4 m high concrete lifts, one on top of the other.
After each wall section was cast the earth within the ring was excavated, and with the aid of the cutting shoe, the caisson walls sank under their own weight. The annulus between the outside of the walls and the cut profile was filled with bentonite assisting the caisson’s even rate of descent and prevent collapse of the external ground.
Another challenge was protecting and maintaining the integrity of the live 910 mm North Harbour Water Main which runs directly alongside the new tank.
The project was run in a collaborative manner, with all parties contributing to its success through innovative design and construct solutions. A minimal site footprint on a main local road which reduced the impact to local residents was achieved through detailed planning of access shaft locations, their construction and the pipe installation method.
Other elements of the project included:
- a new tank overflow to the adjacent Waikumete Stream
- a new network sewer in Harold Moody Reserve
- 800 m of a new transmission sewer, 10 m deep, along Glendale Road from Ceramco Park to Harold Moody Reserve
- a new transmission sewer through Sherrybrooke Esplanade and Parrs Park, including a new box culvert, associated connections, and chambers
- a new network sewer from Rangeview Road to Sherrybrooke Esplanade, including drilling underneath the NIMT railway and construction of a pipe bridge over Waikumete Stream.
Watch a timelapse of the tank construction
