New Zealand’s largest water company, Watercare is seeking expressions of interest to construct Auckland’s new Central Interceptor wastewater project. The scheme includes the boring of a 13km long, 4.5m i.d. tunnel. In detailed design for the last three years, bids will be invited for the construction of the Central Interceptor in two stages.
- Expression of Interest (from 20 October 2017) – which will pre-qualify up to four contractor consortia
- Request for Proposal (2018) – to award a contract for construction of the works The EOI will be released via Watercare’s e-procurement portal, Tenderlink.When complete, the Central Interceptor will greatly increase capacity in Auckland’s wastewater network. The tunnel will run for about 13km from the suburb of Western Springs to Mangere, and lie between 15 and 110m below ground level. Constructed by EPBM, the 4.5m i.d. tunnel will link to 4.4km of sewers ranging in size from 2.1 to 2.4m i.d.Driven through weak sandstone, the tunnel may encounter mixed face materials as Auckland’s geology is overlain with volcanic soils and rock. The southern end of the tunnel is driven through marine and alluvial sediments, and will extend under the Manukau Harbour.The main tunnel terminates in a lift pump station that will be constructed at the Mangere Wastewater Treatment Plant. Shafts for the station will be constructed by D-Wall methods and feature a dual cell configuration approximately 40m deep. The cells will be 12m and 26m in diameter. The pumps will deliver up to 6m3/sec via two 1.4m diameter high density polyethylene rising mains into the treatment plant.
Built under urban, central Auckland, connections into the existing network will be via 16 cascade drop shafts that are between 25m and 70m deep, and range in diameter from 3m to 12m.
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Land for the shafts has been protected by designations and is either owned by Watercare, or its parent organisation Auckland Council. These latter locations are in parks. An option exists to dispose of tunnel spoil at a landfill operation managed by Watercare.
Watercare intends construction to begin in 2019 and be completed by 2025.