The Moawhango-Tongariro tunnel, Paradise Valley, geology and anticipated tunnelling conditions

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Paterson, B.R. 1973 The Moawhango-Tongariro tunnel, Paradise Valley, geology and anticipated tunnelling conditions. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 166 5 p.

Abstract: In Moawhango Heading a fault was intersected at construction footage (C.F.) 15,870 feet in May 1972. Until recently, tunneling conditions have not been favourable and the rate of excavation progress has been low. At present this heading is being excavated on full face in rock of very good quality, with only minor ground water inflows. The tunneling conditions during the last 80 feet of excavation have been the most favourable since May 1972, and the contractor is taking advantage of this improvement to install a lay-by. Excavation has now reached C.F. 16,640 feet and it is anticipated that a significant zone of weakness (probably a fault) may be intersected in the vicinity of C.F. 16,850 feet. Also a re-interpretation of seismic data indicates that a significant weakness in the rock may occur near C.F. 17,900 feet. If both of these proposed features are of major significance, the rock in the section of the tunnel between them is likely to contain numerous shears of subparallel to these main faults. At the present limit of excavation is only about 200 feet from the first of these features, caution should be exercised as excavation proceeds. (auth)