Hūnua 4 Section 11

Customer: Watercare

Contract: Design & Construct

Fast Facts

3.5 km trunk watermain
1.6 m OD diameter steel liner and 3 m OD diameter concrete casing
80% of the pipeline construction was trenchless to reduce disruption to the community
Three small sections at the beginning, middle and end of the route were trenched.
Only 50 to 75 metres of trench was open for construction at one time to reduce impacts on stakeholders and better manage traffic and access.
A 55 tonne Herrenkenecht TBM was used to excavate the 3 m diameter tunnel, with six jacking and reception shafts
At the deepest sections the tunnel runs almost 30 m below ground
The 1575 mm OD, spiral-welded, cement-lined steel pipe were 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 massive Hūnua 4 project, from Market Road to the Khyber Pass Reservoir.

The project is Auckland's biggest water project and comprises a new 31 kilometre long watermain that connects Watercare’s reservoirs in Manukau to central city water storage, improving capacity and the resilience of Auckland’s water network. The project started in 2012 and was completed 10 years later.

Using predominantly microtunnelling methods, we constructed 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. The pipe jacks are the longest ever completed in New Zealand.

The challenge

The alignment for Hūnua 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.

The solution

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 ensured the project work didn't conflict with construction on the City Rail Link, which was underway in Eden Terrace. 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 reduced 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.

We started construction in October 2018 and completed it on time.