Riddolls, B.W. 1976 Investigation of slopes, Palmerston North-Gisborne railway viaducts, near Ormondville, S. Hawkes Bay. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 248 28 p.
Abstract: The engineering assessment of three viaducts on the Palmerston North-Gisborne railway has required the detailed investigation of nearby slopes, some of which have been unstable in the past, and have variously affected the approaches to two of the viaducts. Six Calweld Shafts were drilled to enable direct inspection of the unstable slope materials , which are typically composed of a thin layer of loose gravelly clay overlying mainly very weak bedrock. At Kopua, alluvial silt has also been unstable. Movement appears to have occurred along planar surfaces that probably originated from slope failures along bedding in the bedrock, during the formation of the present drainage. It is considered that the likelihood of further movement of the bedrock is low, and that future structures could be founded in it with safety. (auth)