Engineering geology of the Rangipo powerhouse access tunnel

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Grammer, T.R. 1978 Engineering geology of the Rangipo powerhouse access tunnel. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 311 18 p.

Abstract: The Rangipo Power Project, presently under construction, is located along the western edge of the Kaimanawa Mountains. The project will generate hydroelectric power by using a natural head developed along the Tongariro River between the Moawhango Tunnel outfall and the Poutu Intake. The Rangipo Powerhouse is located 100 m underground, below the south bank of the Waikoko Stream. From an intake at the Rangipo Dam, water will be carried to the powerhouse via an eight km headrace tunnel. Water will leave the powerhouse by way of a three km tailrace tunnel which will outfall at Beggs Pool. A 600 m Access Tunnel was driven to provide construction and vehicle access to the underground powerhouse cavern and the tailrace surge chamber cavern. The access tunnel is a 6 m x 6 m D-section tunnel driven on a down grade of 1 in 9.5 for 600 m beyond which it levels out to intersect the main floor level of the powerhouse at RL 583.9 m at tunnel distance 647.5 m. The tunnel was excavated using mainly full face, drill, and blast technique. (auth)