NIMT electrification: engineering geological report on the daylighting of tunnel 10 (Mangaweka) and tunnel 11 (Taihape)

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Read, S.A.L. 1982 NIMT electrification: engineering geological report on the daylighting of tunnel 10 (Mangaweka) and tunnel 11 (Taihape). Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 374 15 p.

Abstract: The design of open cuts to daylight Tunnel 10 (Mangaweka) and Tunnel 11 (Taihape) as part of the electrification of the North Island Main Trunk Railway is being carried out by Ministry of Works and Development (MWD). Engineering geological advice for the design of the two cuts has been requested by MWD from New Zealand Geological Survey. Tunnel 10 is sited in homogenous siltstone of the Mangaweka Mudstone and the majority of the 60 m high cut would be in this lithology. As slopes at angles greater than 50 degrees fail by slabbing cut slopes a 1:1 are recommended. Colluvium exists at each end of the cut and the top of the cut will be in gravels, silts and loess. Tunnel 11 is sited in varying lithologies of the Taihape Sandstone and with a fault zone crossing the cut. Four terraces each underlain by gravels and loess occur irregularly throughout the cut which has a maximum height of 42 m. Batter angles of 1/2:1 are recommended for the majority off the cut.