Paterson, B.R. 1974 An appraisal of the resistivity survey in Paradise Valley, Moawhango-Tongariro tunnel. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 201 5 p.
Abstract: At the request of the N.Z. Geological Survey a resistivity survey was carried out in the Paradise Valley area along the Moawhango-Tongariro tunnel line, by G.B. Dawson Geophysics Division D.S.I.R. The main purpose of the survey was to define the depth to the ground water table particularly in the 7000 feet section separating two exploratory holes that were drilled by the Ministry of Works and Development. Having defined the position of the ground water table the hydrostatic head above the tunnel at these points could be calculated and the maximum hydrostatic pressures likely to be exerted on the concrete tunnel lining could be more accurately assessed. Prior to these investigations high ground water pressures had been encountered in a section of the tunnel being excavated beneath Paradise Valley. The vertical cover is approximately 800 feet in this area and it was considered necessary to carry out these investigations ahead of the tunnel face where the vertical cover increased to a maximum of 1700 feet. In this report the results of the drilling and resistivity survey are discussed with particular reference to the ground water hydrology and the subsurface geology. Data from the resistivity survey are related to the geology in the excavated section of the tunnel as well as the anticipated rock condition several thousand feet ahead of the present tunnel face. (auth)