Climatological influences of deep seated translational landslides in residual clay shale bedrock

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Slow-moving landslides present large economic risks to high-value infrastructure such as roadways and railways. Two specific examples include strategic Western Canadian transportation corridors such as the Yellowhead Highway in Saskatchewan and the Thompson River Valley rail corridor in British Columbia (BC). Ongoing movements at these locations are creating risks in terms of increased maintenance costs, and economic losses associated with infrastructure closure following slope movement. This proposed research will explore the interactions of two key failure mechanisms associated with these landslides: the behaviour of pre-sheared bedrock and the influence of meteorological effects on delayed failure resulting from progressive softening. Semi-arid climates are subject to wide swings in pore-pressure dynamics and produce seasonal or inter-annual pulses in the rates of net percolation into deeper groundwater systems. The impact of these pore-pressure dynamics on the development of failure surfaces is not well understood for large, deep-seated translational landslides. These climate-driven pore-pressure dynamics are often compounded by fluctuations of the water levels in deeply incised river valleys along which transportation infrastructure is constructed. These cyclic pore-water pressures can result in strain softening, leading to progressive displacement of the slope. Although the river level adjacent to the slope can provide a stabilizing surcharge force when the water level is elevated, it can also result in pore pressure build up within the slope, which dissipates more slowly than the subsequent drop in river levels following peak flood events. The proposed research will incorporate a combination of field testing and monitoring, laboratory testing, and numerical modelling designed to characterize the ground movement of very slow-moving landslides in central Saskatchewan and central BC. Instrumentation will be installed within the slopes to supplement existing monitoring. Conceptual (qualitative) and numerical (quantitative) modelling will be used to demonstrate the linkages between pore-pressure dynamics and river erosion on the evolution of strain and changes in the stability of the slide mass. ****************