Engineering geological factors related to collapse of Ruahihi canal

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Oborn, L.E.; Northey, R.D.; Beetham, R.D.; Brown, I.R. 1982 Preliminary report on engineering geology in the area of Ruahihi canal collapse. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 361A. 17 p.

Abstract: The geology of the Ruahihi area consists of a sequence of ignimbrites, tephras and ashes, some of which have low strength, high sensitivity, low density, high permeability, and are susceptible to collapse and possibly dispersion. The section of canal that failed was constructed close to a steep natural slope of marginal stability that later had Fill A placed against it. After canal filling, groundwater levels rose and contributed to the instability of fill and natural ground. At the same time there was significant settlement of the forebay and canal. It is judged that various geological factors and mechanisms, possibly including hydraulic fracture and dispersion, contributed to the canal failure. (auth)