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UBC Theses and Dissertations

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UBC Theses and Dissertations

Terrain mapping and regional slope stability evaluation in the Fraser Canyon, British Columbia Bell, Alison

Abstract

Terrain analysis of the 22-mile (32.5 km) Fraser Canyon between China Bar and Yale, British Columbia, is the theme of this research. Micro-, meso-, and macro-scale variables are differentiated as a basis for slope stability evaluation. Relationships between slope failure and meso-scale slope attributes only are examined in detail. Surficial materials are classified according to the ELUC terrain classification system in terms of texture, genesis, form, and surface-modifying processes. The materials are mapped to an elevation of 1500 feet (640 m) as terrain units on an air photo mosaic at the approximate scale of 1:25,000. The terrain map is the first example of the application of the ELUC classification scheme in the Fraser Canyon. Twelve meso-scale slope attributes describing surficial and bedrock geology, slope geometry, and anthropogenic effects are evaluated at sites at 0.1 mile (0.16 km) intervals along railway lines on both sides of the canyon. A 20-year railway maintenance record along the eastern canyon side is the source of slope failure data. An Automatic Interaction-Detector (AID3) program is used to determine which attributes contribute most to the explanation of variation in slope failure incidence along the eastern slopes. Six attributes are the most important contributors: surficial material(s), surface-modifying process(es) , slope height above and distance away from the railway tracks, angle, and the presence or absence of excavation. Together the variables explain 41.4% of the total variation of failure incidence. The most significant variable is surficial material. Colluvium is the most common surficial material, comprising 60.5% of all slope sites. Bedrock units along the eastern slopes exhibit the highest mean incidence of failure with 3.0 3 events per site over the 20-year period, followed by colluvial units at 1.95 events per site. Fluvial and fluvio-glacial sites show the lowest mean incidence of failure, with 0.24 and 0.4 8 events per site, respectively. Sites where the slope has been excavated during railway construction (80% of the total number) experience above-average failure incidence, where the average for all sites is 1.84 events per site. Where the trackside slope angle is greater than 41° in unconsolidated material, and greater than 70° in bedrock, above-average failure incidence occurs (3.03 and 2.15 events per site, respectively). Guttmannv- Lingoes multi-dimensional scalogram analysis (MSA-T)and a clustering program (HCLUS) are used to group the sites on the basis of the six most influential slope attributes. The resultant categories do not display significantly different failure means. Classification of sites on the basis of surficial material only yields broad hazard categories, in which bedrock and colluvial sites fall into high and intermediate classes, respectively. The value of this research is that it provides a method for regional slope stability evaluation at the reconnaissance stage of a development proposal.

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