A rare case of downward progressive failure in eastern Canada: the 1976 Saint-Fabien landslide

The Saint-Fabien landslide occurred in December 1976, 270 km northeast of Quebec City, Canada. took place a valley filled with glaciomarine sensitive clay covered by peat bog deposits and presenting an upwards hydraulic gradient. Unique features this event are the ground surface failure that both close to horizontal. In addition, passive active zones were observed debris after landslide, indicating possible downward progressive mechanism, rarely Eastern Canadian clays. Possible triggers are: continuous exploitation downslope (or) roadworks going on along Road 132 at time event, which is crossing area upslope. Conventional stability analysis for site gives factor safety 1.43, limit equilibrium cannot explain formation Saint-Fabien. initiation propagation analysed through 1D numerical modelling using concept failure. methodology consists two steps: first calculation initial stresses slope finite element software PLAXIS 2D; second, potential code BIFURC, developed Norwegian Geotechnical Institute. Results from BIFURC show able extent parameter values based what was measured situ.