On 11th September the TBM Hiwa-i-te-Rangi broke through into the 30-m deep shaft at the Western Springs site. The TBM Had tunnelled a little over 13km and installing over 8100 segment rings as she builds the 16.2-km Central Interceptor tunnel from Māngere to Point Erin, Herne Bay.
Western Springs was the original end point for the tunnel. When the Central Interceptor construction contract with Ghella Abergeldie JV was signed in 2019, the tunnel was due to finish at Western Springs. Since then, it has twice been extended all the way to Point Erin.
The project will significantly improve water quality at Tāmaki Makaurau beaches and in waterways by reducing 80 per cent of wet weather overflows in Auckland.
The TBM is currently lying 25m below ground just south of MOTAT. Hiwa-i-te-Rangi began tunnelling in August 2021. Since then, she has crossed under the Manukau Harbour and passed through the 110m-deep Hillsborough Ridge (the deepest section of the route). The 4.5m diameter tunnel has a 1:1,000m gradient, so that wastewater will flow downhill by gravity all the way from central Auckland to Māngere Wastewater Treatment Plant for processing.
From here on in the TBM will be encountered favourable ground conditions, helping it to continue tunnelling north safely and efficiently to complete the tunnel by mid-2025.
Elsewhere on the Central Interceptor project, construction on two link sewers that intersect the main tunnel have been completed. Testing is underway at the new Māngere Pump Station, which will send flows from the tunnel to the treatment plant and the tunnel is being connected to local wastewater networks along the tunnel route. Preparations for excavation of a shaft at the Point Erin site is underway. Section one of the tunnel (from May Rd, Mt Roskill south) will be ready for operation by the end of the year. The Central Interceptor project is due for completion in 2026.
For further information click here and nz/18 for the tunnelbuilder archive. Visit https://www.ghella.com and https://www.watercare.co.nz/. 37/24.
