Slope stability investigations in Castle Hill Basin.
Thesis DisciplineEngineering Geology
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
The field area of interest is an intermontane basin lying 100 km northwest of Christchurch on the West Coast Road. Within this roughly triangular, tectonic depression lies a sequence of marine and non-marine sediments of late Cretaceous-Tertiary age. The sediments have been modified by glacial and post-glacial events to leave steep-sided valleys, flights of terraces and limestone hills. Landslides of all types (falls, slides, slumps, flows, complex movements and mass wasting) are found in the dense, heavily overconsolidated sands, silts and muds. The different types of landslides and their, distribution with respect to lithology and structure is discussed, as is the rates of degradation and their relative age. A select area around Broken River - Hogsback Stream is studied in detail and the stratigraphy, structure and geohydrology is presented. The sediments from the Enys Formation were sampled, tested for index and physical properties, and interpreted in terms of their significance·towards slope stability. A major slump of this area is back-analysed using parameters gained directly or inferred from the geotechnical testing. Several methods are used and a circular arc mode of failure is rejected in favour of a block slide bounded by passive and active wedges. Finally the landslide processes and factors that have been found operating in Castle Hill Basin are outlined and it is seen that the most important factors are those relating to the area's intrinsic climatical, geological and topographical nature. These processes and factors are summarised in a series of maps, which, when overlain, produce a landslide susceptibility map showing predicted areas of likely movement.