Engineering geology of lower Kawhatau route, Utiku-Mangaweka railway deviation

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Riddolls, B.W. 1972 Engineering geology of lower Kawhatau route, Utiku-Mangaweka railway deviation. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 142 7 p.

Abstract: The Lower Kawhatau section of the deviation is situated in a narrow valley, which from field and drilling investigations is shown to be formed by sandstone, with gravel occurred up to 50 feet beneath the valley floor. Slopewash deposits of sand and silt are present in most places. The valley was eroded and gravels deposited by a former river that was subsequently captured during the development of the existing drainage pattern. The route requires cuttings up to 70 feet deep, mostly in gravel and slopewash, but the northern margin of the gravel deposit was not defined accurately, and sandstone may also be encountered. The slopewash is the weakest of these lithologies, and will not be as stable as the gravels in steep cuttings. Failure of parts of the cutting could eventuate if the probably steeply dipping contact between gravel and sandstone is intersected. Additional investigations could determine the likelihood of this occurence. (auth)