Pumping test effects on groundwater and settlement for Waterview tunnel
Annual Conference
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The New Zealand Transport Agency has applied to construct 5 km of new state highway in Auckland as part of the Waterview Connection project including a 2.5 km tunnel section excavated primarily within the East Coast Bays Formation (ECBF) of the Waitemata Group. Depending on the approach to tunnel construction, any inflows to the tunnel and the subsequent drawdown of groundwater levels may cause settlement of compressible soils, which may result in settlement of overlying structures. Other effects include the potential to reduce base flows in nearby Oakley Creek and the potential to spread contaminants from former landfill areas.
This paper describes two contrasting long duration pumping tests with an unusually comprehensive monitoring regime. The approach was designed to help assess the potential effects of constructing the tunnel in “open mode”. Although the pumping bores are close together, the response to pumping was very different with the first test located in an area of significantly higher permeability.
The data from the pumping tests on the behaviour and variability of the Waitemata Group and overlying formations will inform selection of the construction method for the tunnel and improve understanding of the potential effects, and will also be of benefit to future projects within the same hydrogeological setting.