The project
The Central Interceptor is Watercare’s 16.2km wastewater tunnel beneath Auckland — the largest wastewater infrastructure project in New Zealand’s history. Working for the Ghella Abergeldie Joint Venture (GAJV), RPC engineered, manufactured, delivered and installed nine GRP cascade and maintenance shafts, from 3m to 7.5m in diameter, that join the tunnel.
In 2020 RPC was awarded the Central Interceptor Cascade Shafts project, recognised as the largest diameter and deepest GRP shafts constructed globally.
The challenge
- Depth and scale. May Road shaft A is 7.5m in diameter and approximately 70m deep — one of the deepest shafts ever to be sunk and lined in the Southern Hemisphere — built from 23 segments.
- Moving very large parts. The 7.5m-diameter segments from Corio were 3.1m high and weighed 12 tonnes each. Each was transported by road in the early hours of the morning, taking up three lanes of traffic with an escort crew of 12 personnel.
- A five-year programme through a pandemic. Manufacturing began in November 2020, and the project navigated the significant disruptions caused by the Covid-19 pandemic.
What RPC did
Segments were assembled above ground on site, then lowered into the excavated shafts. At May Road, the last five segments were assembled into a module 15.5m high. This 67-tonne module was installed in a single lift, completing the 7.5m diameter by 70m deep GRP cascade structure. The annulus between the rock excavation and GRP modules was then back-filled with concrete by the GAJV team.
At Tawariki, the DN7500 modules, each weighing up to 32 tonnes, use flanged connections that facilitate rapid assembly on site, thereby reducing construction time. Once installed, each module is encased in concrete to create a corrosion-resistant shaft liner with no exposed concrete surfaces.
Selected shafts:
| Shaft | Size | Highlights |
|---|---|---|
| May Road (shaft A) | 7.5m diameter × ~70m deep | 23 segments; final 15.5m-high, 67-tonne module installed in a single lift (Dec 2023) |
| Dundale | 4.5m diameter × 24m deep | Two segments, 11.33m and 12.2m long, weighing 34 and 26 tonnes; plus a 3m-diameter control chamber |
| Rawalpindi | 5.5m diameter × 26.8m deep | Segments made in Batam and Corio (2024) |
| Tawariki | DN7500 × ~25m deep | Modules 8m wide and up to 32 tonnes, flanged for rapid assembly (2025) |
| Point Erin | 3.2m diameter | The final shaft; segments from Batam and Corio (Nov 2025) |
OneRPC in action
Designed in Seven Hills, R&D works at Broadmeadow and manufactured in Batam, Indonesia and Corio, Victoria, this project showcased our ability to engineer and deliver complex, high-performance composite solutions on a massive scale. The Central Interceptor project has been a living example of our commitment and strategy as a company — OneRPC.
