Engineering geology of bridge no.1, Johnsonville railway line

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Oborn, L.E. 1971 Engineering geology of bridge no.1, Johnsonville railway line. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 115 9 p.

Abstract: The position of the Wellington Fault near the site of the proposed bridge is not known. It can be predicted with equal confidence that it lies either at the western abutment, cuts the bridge or its abutment, or lies to the east of the bridge. The scant almost complete lack of positive data clearly makes all possibilities open to question. Sub-surface investigation, mainly drilling but preferably also geophysical exploration, is essential to defining the position of the fault. The eastern abutment will be sited on young marine sediments which will be overlain by weak, probably-hydraulically-placed fill. The western abutment will be on either basement rock or the young marine sediments that overlie basement, depending upon siting; either of these should provide foundations with adequate bearing strength. Landslides engendered by fault movements or earthquakes constitute a threat to the stability of the rock slopes on the railway line north of the bridge. The embankments on the southern approaches to the bridge would be damaged during a severe earthquake or fault movement. (auth)