Hobson Bay Tunnel
Strengthening Auckland’s infrastructure
For 90 years, 25% of Auckland’s wastewater was carried via an unsightly concrete sewer pipe across Hobson Bay to the Mangere Wastewater Treatment Plant. As the city’s population grew, the pipeline strained to cope with demand and overflowed frequently into Hobson Bay.
We replaced the ageing pipeline with a 3km long, 3.4m diameter sewerage tunnel running 35m below sea level from Parnell to the Orakei Domain. The new tunnel provides significant additional capacity to support future growth and virtually eliminates overflows – leaving the bay open to use for swimming and boating. The tunnel connects to a new, higher capacity pump station.
The new tunnel provides significant additional capacity to support future growth and virtually eliminates overflows – leaving the bay open to use for swimming and boating
The pre-cast concrete segmental-lined sewer tunnel was excavated using an earth pressure balance tunnel boring machine – the first of its scale and type in New Zealand. This allowed the tunnel to be built at a shallower depth in weaker ground conditions, thus reducing the project’s whole-of-life cost. Importantly in the high-density urban environment, tunnelling also reduced impacts on surrounding residents.
We constructed the 22m diameter, 37m deep permanent access shaft in Orakei Domain, built new pump stations and demolished the existing pipeline, while McConnell Dowell bored the tunnel itself.