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Possible construction methods for new outfall The onshore section of the new outfall will be built largely by underground tunnelling, much of it deep underground. However in the eastern section of the tunnel where the soils are more susceptible to settlement, the pipeline might be brought much closer to the surface and be installed by open-cut trenching, and pipe-jacking techniques. Once the work is finished the tunnel will be invisible and all areas will be restored to their previous condition. Proposed deep tunnelling method A deep tunnel will be driven from the treatment plant along the first 1.25 km of the route to a point on Maxwelton Drive between the intersections with Coromandel Crescent and Mayfair Crescent. It will be up to 60 metres beneath the ground. Excavated materials from the tunnel will be carried back along the tunnel to the Rosedale Treatment Plant for disposal. Subsurface boring From Maxwelton Dr the remainder of the outfall could be constructed by a combination of open cut trenching and sub-surface boring and pipe jacking down to the foreshore. This will be typically five metres below ground. Trench method Geotechnical investigations have shown us that with these proposed construction methods settlement is likely to range between 20mm and 80mm directly over the pipeline, to 0mm up to 14 metres on either side of pipeline. This area largely falls within the road reserve.
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Water
introduction