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Numerical modelling of large scale toppling Pritchard, Mark Anderson


The principle purpose of this research is to resolve the mode of failure of the Heather Hill landslide, one of several well defined failures in the Beaver Valley, Glacier National Park, British Columbia. Field work led to the preliminary conclusion that some type of toppling process contributed to the failure. A literature review of toppling revealed that large scale topples have never been quantitatively assessed, and that currently used analytical techniques are not adequate. Consideration of alternative numerical techniques resulted in the distinct element method being selected as the best technique for modelling toppling. The Universal Distinct Element Code (UDEC) was purchased and its suitability demonstrated by reevaluating examples of toppling analysis reported in the literature, and evaluating a large scale engineered slope at Brenda mine where toppling is known to occur. UDEC is used to examine and classify the mode of failure of the Heather Hill slide. This research leads to very important general conclusions on toppling and specific conclusions relating to the Heather Hill landslide: UDEC is suitable for modelling all types of topples. The program can be used to back analyze rock mass strength parameters and determine the shape and location of the final failure surface in flexural toppling. A quantitative assessment with UDEC confirms that the base of failure in flexural toppling may be planar or curvilinear, and that pore pressures significantly affect stability. The Heather Hill landslide failed by flexural toppling limiting to a curvilinear failure surface, and the slope immediately north of the Heather Hill landslide is deformed by flexural toppling. The locations of landslides in the Beaver Valley correspond with the occurrence of foliated pelitic rocks in the lower slopes and the boundary between these rocks and stronger grits is the up slope limit. The kinematic test of toppling potential is violated by the Heather Hill landslide. This test is shown to only apply to small scale drained slopes.

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