Methods of excavation in fault zones, Moawhango heading, Moawhango-Tongariro tunnel

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Paterson, B.R. 1975 Methods of excavation in fault zones, Moawhango heading, Moawhango-Tongariro tunnel. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 222 6 p.

Abstract: Serious difficulties are being encountered by the contractor in advancing the tunnel through a fault zone in Moawhango Heading at construction footage 25,140' - 25,200'. As a result very little progress has been made during the last seven weeks. The contractor has used standard methods of excavation to tunnel through this zone, with the result that the situation has deteriorated progressively from the time at which the zone was first intersected. The use of similar methods in fault zones previously encountered has proved the inadequacy of the techniques, which do not permit progressive caving to be arrested at an earlier stage. As fault zones are numerous in the Kaimanawa Greywacke, and are often similar, and hence predictable in composition, it would be possible to develope a technique best suited to the conditions they present. Furthermore, as most of the excavation difficulties in this rock are caused by fault zones, improvement in techniques should increase excavation progress. These points were raised at a meeting between the Contractor and Inspection and Design Engineers on 3 June 1975. Some of the points have been discussed previously at meetings, and have been emphasized in previous reports. With approximately 11,000 feet remaining to be excavated in the tunnel, it is in the interest of the contractor and Ministry of Works and Development and supervising authority, to examine alternative techniques. In addition, with future underground works planned in Rangipo Project, to be undertaken in similar rock by contractors and M.W.D. forces, there is incentive to improve tunneling methods and performance where possible. (auth)