UBC Theses and Dissertations

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UBC Theses and Dissertations

The perpetual landslide Summerland, British Columbia Riglin, Linda Diane


The purpose of this study is to understand the environment for failure of the Perpetual Landslide. To achieve this objective a field investigation was carried out to evaluate the movement pattern of the slide and its geologic and hydrologic environments. This information, along with ground water flow and stability models was used to define major controls on stability. The following points are made: (1) The slide moves by rotation and translation of blocks with a transition to flow movement at the toe. (2) At depth, the failure surface lies within the Tertiary sedimentary rocks. Exposed gouge consists primarily of clay (most likely remolded claystone and some clay-rich till) with dispersed pebbles and rock fragments. (3) Discontinuities including inherent heterogeneity between and within geologic units, weathering, and jointing are significant to the unstable situation. (4) Changes in stress equilibrium, particularly those caused by removal of overburden and lateral support with downcutting in Trout Creek Canyon, are likely important in the origin of the slide. (5) The proposed mechanism of failure is: (a) The progressive reduction from peak to residual strength of the claystone. (b) In addition to the high water table, high pore-water pressures along the failure surface. At the present time, the slide's continuous movement is acting to establish a new stability in equilibrium with this ground water flow system and lower strength.

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