D. J. Hutchinson

Geomechanical interpretation of the Downie Slide considering field data and three-dimensional numerical modelling

Downie Slide has been interpreted as a massive, composite rockslide, and a number of landslide zones have been defined based on the interpretation of morphological features and a detailed assessment of spatially discriminated slope behaviour. Key factors controlling the mechanics of massive slow-moving landslides can be interpreted through the observation and detailed study of the slope behaviour and physical characteristics. Once identified, key components influencing slope deformation can be tested using three-dimensional numerical models. Two series of numerical simulations have been developed to test how explicitly defined internal shear zones, and the interaction between landslide morphological regions, influence global landslide behaviour. Results from these numerical simulations, when compared to field monitoring data, indicate that internal shear zones have little influence on Downie Slide deformation, while the interaction between morphological zones plays a larger role in slope kinematics.

Downie Slide: numerical simulation of groundwater fluctuations influencing the behaviour of a massive landslide

Groundwater levels at Downie Slide have varied during the development of and over the operating life of the Revelstoke Reservoir. Drainage system construction successfully lowered groundwater levels through the central portion of the slope; reservoir filling resulted in water table rise near the inundated toe, and over the operating life of the hydro-electric facility gradual, minor losses to the drainage system capacity have resulted in a slow rise in water table levels. Calibrated models capable of reproducing observed deformation patterns at Downie Slide have been tested with changing groundwater levels. Models perform well, adequately reproducing observations of global slope response to changes in piezometric boundary conditions. These models have also been used to test potential trigger scenarios, including rapid reservoir drawdown and a total loss of drainage system capacity.