Modelling the impact of deep fractures on groundwater flow and slope stability in post-glacial marine clays (Quebec, Canada)

It is usually assumed that post-glacial marine clay deposits, such as those found in Quebec, are generally intact below a shallow fractured crust (3 to 5-m depth). However, recent work has shown the presence of hydraulically-active fractures to depths of down to 16-m. In light of this finding, the potential impacts of these fractures on groundwater flow dynamics and slope stability are explored by comparing field data with the results of transient and steady-state groundwater models with and without fractures. Two slope geometries that exhibit contrasting groundwater flow directions and different fracture scenarios were considered. The results of the hydrogeological modelling were then imported into a slope stability model to determine how the hydraulic effects of these fractures impact slope stability. Results show that fractures increase hydraulic head when they act as preferential pathways for infiltration, but can also reduce hydraulic head by acting as pathways for water to more quickly exit the formation within the slope face. Therefore, from a hydrogeological perspective, fractures could improve or reduce slope stability depending on the groundwater flow system. As this study only addressed the hydrogeological impact of the fractures, future work should focus on the coupled hydromechanical impacts of these features.