Contract: Design & Construct
Location: Auckland, New Zealand
Budget: $48 million
- 3.5 km trunk watermain
- 1.6 m OD diameter steel liner and 3 m OD diameter concrete casing
- 80% of the pipeline construction will be trenchless to reduce disruption to the community
- Three small sections at the beginning, middle and end of the route will be trenched.
- Only 50 to 75 metres of trench will be open for construction at one time to reduce impacts on stakeholders and better manage traffic and access.
- A 55 tonne Herrenkenecht TBM will be used to excavate the 3 m diameter tunnel
- six jacking and reception shafts
- At the deepest sections the tunnel will run almost 30 m below ground
- The 1575 mm OD, spiral-welded, cement-lined steel pipe will be installed in 12 m sections and welded together in situ.
McConnell Dowell was awarded the contract to design and construct Section 11, the final section of the pipeline, from Market Road to the Khyber Pass Reservoir. Using predominantly microtunnelling methods, we will construct a 3.5 km watermain using a tunnel boring machine (TBM) to drive and install 2500 mm ID jacking pipes between six shafts, before lining the tunnel with a 1575 mm OD steel pipe. Once complete, the pipe jacks will be the longest ever completed in New Zealand.
The Hunua 4 project, a new 31-kilometre long watermain has been underway since 2012, with sections up to Market Road, Epsom now in service. Once complete it will connect Watercare’s reservoirs in Manukau to central city water storage improving capacity and the resilience of Auckland’s water network
The proposed alignment for Hunua 4 Section 11 ran from Market Road in Epsom to Khyber Pass in Grafton and amongst residential properties, major arterial roads, schools and businesses. Constructing the pipeline using traditional open-cut methods would have caused major disruption to the surrounding community. Difficult geotechnical conditions, ranging from very hard basalt to soft clays created further challenges.
We proposed an alternative alignment that re-routed the pipeline along Manukau Road and under the Southern Motorway (SH1), moving construction away from residential areas, avoiding sensitive ecological and heritage sites. The new alignment will also ensure the project work doesn’t conflict with construction on the City Rail Link, which will be underway in Eden Terrace soon. We also developed state-of-the-art trenchless technologies to install the pipe almost entirely below and within the road or motorway corridor which will dramatically reduce impacts on local residents, businesses and traffic.
Key to success
Close relationships with consultants was key to developing and delivering our innovative solution. We worked with McMillen Jacobs Associates to develop the permanent works design and prepare an Assessment of Environmental Effects report to secure resource consent for the project.
Close engagement with the community, businesses, residents, local schools, mana whenua, Auckland Council and Auckland Transport is an integral part of successfully delivering this project in what is a highly-visible, constrained urban environment.
Construction started in October 2018 and is scheduled for completion in late 2020.