Firth proves its expertise on Auckland's Central Interceptor project
Firth has played a key role in solving complex challenges on the Central Interceptor, a $1.668 billion wastewater tunnel designed to transform Auckland's water quality. Delivered by the Ghella Abergeldie JV, the project will significantly reduce environmental overflows and features a 16.2km, 4.5m internal diameter tunnel running from Grey Lynn to Māngere Wastewater Treatment Plant.
Concrete is fundamental to the success of the Central Interceptor, forming the tunnel lining, structural support, and ensuring the long-term durability of the infrastructure. Given the harsh underground environment - characterised by acidity, pressure, and moisture - the project depends on specially engineered, high-performance concrete designed to meet a 100-year lifespan.
Lyon Ave Caisson Wall for the Central Interceptor project for Watercare
Although not originally named as the preferred concrete supplier, Firth was brought in to develop a solution for the Lyon Avenue caisson wall, a critical component of the project.
“We were asked to design and place a grout to fill the 70 mm annulus gap left behind by the cutting shoe, joining the external wall of the caisson with the ground, to hold up the weight of the concrete,” explains John Boules, Technical Sales for Firth. “The caisson stands at a height of 39 metres and weighs approximately 1,000 tonnes.”
Low Viscosity Annulus Grout Supply
“At Firth we recognise that delivering concrete is not just about the material; it's about delivering solutions that cater to our clients' unique requirements, which is why we worked closely with the Ghella Abergeldie JV to collaboratively deliver an innovative grout solution for the Central Interceptor in Auckland.”
“We developed a highly specialised grout, with an ultra-low viscosity that approximated that of water, to ensure the 100 bar pressure limit on the grouting system wasn’t breached. In addition, this grout had to comply with the required 28-day characteristic compressive strength of 40MPa and remain fluid for over 50 hours. This latter attribute was crucial to the grouting process which was planned to be a continuous multi-day pour, requiring small-batch manufacturing and delivery processes by our Firth teams. Everything went to plan even though the ground was saturated from heavy rain. The pour was completed in only 17 hours utilising 75m3 of this specially crafted mix.”
John’s efforts were not only a huge help to the project which won Firth a Technical Excellence Award at the Concrete NZ Conference in 2024, they also meant Firth continued to work with the Italian JV Ghella Abergeldie on the Central Interceptor supplying a staggering 21,000 m3 of concrete to the project to date.
“Although we didn’t start the project as preferred supplier for the Ghella Abergeldie JV, after supplying them with a solution for the Lyon Ave Caisson Wall we continued to be asked for concrete which we were happy to do.”
John says that due to Firth’s efforts on this project (scheduled for completion by June this year), they have now been awarded supply on the ‘Herne Bay Collector’ - another Watercare project being delivered by tunnelling company Ghella.
Watch this space.
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Central Interceptor facts and figures ...
In combination with Watercare’s new Central Interceptor tunnel, the Herne Bay collector tunnel will collect combined wastewater and stormwater overflows for safe treatment at Māngere Wastewater Treatment Plant. This new infrastructure will significantly reduce overflows into the environment and improve the quality of our swimmable beaches. A 2.1m-diameter tunnel will be bored for approximately 1.5km using a micro-Tunnel Boring Machine. The pipeline will pass beneath the streets at depths ranging from 9-22 metres. |
Benefits
- Environmental Protection: Drastically cuts wet-weather sewage overflows into Manukau Harbour and local waterways.
- Capacity Expansion: Provides essential infrastructure for Auckland's growing population, allowing for future residential and commercial development.
- Asset Management: Extends the life of the existing wastewater network and provides storage for over 250,000 cubic metres of wastewater.