The Moawhango-Tongariro tunnel. Paradise Valley - a re-interpretation of the geology and the anticipated tunnelling conditions

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Paterson, B.R. 1972 The Moawhango-Tongariro tunnel. Paradise Valley - a re-interpretation of the geology and the anticipated tunnelling conditions. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 134 4 p.

Abstract: A fault zone which has seriously affected the progress of the Moawhango Heading has been intersected at the construction footages 15,770 - 15,790. This zone consists of intensely fractures rock with interstitial clay and discrete clay seams, and has large ground water inflows associated with it. When first encountered, the ground water flowing into the tunnel from this zone was very cloudy with clay in suspension. After excavation of this one pressure began to be exerted on the steel sets, probably as a result of the relaxation of the shattered rock as clay was progressively removed by groundwater. High ground water pressures were encountered within this zone during subsequent grouting activities. These facts indicate that a significant zone of weakness has been intersected beneath Paradise Valley. The pressures of the groundwater within this zone suggest that any similar fault intersected in the vicinity of Paradise Valley could produce tunneling problems of a magnitude similar to those experienced at footages 15,770'-15,790'. In the light of this situation a re-appraisal of the geology and the anticipated tunneling conditions beneath Paradise Valley has been undertaken in an attempt to find any further faults that would intersect the tunnel line in this area. Plan 100/M/61 is appended to this report. (auth)