Characterization of a landslide-prone glaciolacustrine clay from the Thompson River Valley near Ashcroft, British Columbia

  • Author / Creator
    Le Meil, Gael
  • Several large landslides have occurred in the Thompson River Valley near Ashcroft, British Columbia. The movement of these landslides have presented challenges for the operation of the two national railways that traverse this valley. The landslides are multiple retrogressive, translational, slow-moving and occur within glaciolacustrine clay. In this study, continuous core samples were collected from the Ripley slide (velocity in the order of 80 mm/year; volume 1.0 × 106 m3) for characterizing the glaciolacustrine clay. The x-ray radiography and logging of the core revealed interbedded silt and clay, interpreted as a glaciolacustrine stratigraphic unit. It includes brown, fat, slickensided clay beds. The glaciolacustrine unit was found to be stiff and heavily overconsolidated (σ’p ≥ 2000 kPa). The objective of the laboratory tests was to characterize the shear behaviour and strength of the glaciolacustrine clay, in particular the pore water pressure response and development of residual shear strength. Direct shear, ring shear and direct simple shear (DSS) tests were conducted. Test results showed that clay-dominated beds have a greater potential for shear strength reduction than silt-dominated beds. Softening and orientation of platy clay particles in the direction of shear reduce the drained shear strength. After large strains were imposed in the direct shear and ring shear tests, slickenside-like shear surfaces were formed in clay-rich samples. At the Ripley slide, clay beds exhibit a low residual friction angle (φr’ = 12°). Low residual shear strength was correlated with high plasticity (LL = 84%). Plastic clay-rich beds are weak soil horizons. Where they are persistent, they are the preferential location for retrogressive failures to occur. Two such clay beds are responsible for the major landslides of the Thompson River Valley. These clay beds were found to host the Ripley slide’s active rupture surfaces (elevations 257.3 and 268.8 m).

  • Subjects / Keywords
  • Graduation date
    Fall 2017
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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