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UBC Theses and Dissertations

Distinct-element modelling of intermittent deformation behaviour and fatigue in two large rock slides Smithyman, Megan


This thesis reports the assessment of two large, slow moving landslides. The Campo Vallemaggia slide is located in the southern Swiss Alps, and has a recorded history of movements dating back hundreds of years. The other slide, Little Chief, is located in British Columbia, and is affected by toe submergence due to the presence of a dam. These slides have well developed sliding surfaces along which the majority of the movement takes place. A process of modelling the effects of time, involving different water tables to represent the wet and dry seasons of the year, was undertaken using UDEC (Universal Distinct Element Code, Itasca, 2009). The models were run with first the high, then low water tables, alternating repeatedly to represent model years. They were analyzed for signs of fatigue, internal deformations and long term movement trends. The Little Chief Slide was also analyzed using this method to verify the positions and existence of the sliding surface. Mohr-Coulomb plasticity was applied to both slides, and found to be sufficient for representing the Campo Vallemaggia slide, and developing fatigue indications. A sharp drop in the number of yielded elements in the model was seen at approximately 1300 years. This coincided with a slowing of the model movement and a change in the rate of opening of a fault. This was concluded to be similar to the fatigue effect commonly seen in metal. However the Little Chief slide did not develop as desired under this constitutive model, therefore the strain softening plasticity criterion was applied to this slide for models that investigated internal deformation of the sliding mass, and those focussing on development of the sliding surface. Initial strain softening models using the properties expected for the site did not give satisfactory results, likely due to geologic and geometric complications not captured in a two dimensional model using a homogeneous rockmass. Instead, lowerbound properties were applied to the slide, resulting in the development of a sliding surface similar to that interpreted at the site. As well, significant internal deformation was found using these properties, including some suggestive of a fatigue effect.

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