Hydrogeology of a complex Champlain Sea deposit (Quebec, Canada): implications for slope stability

Abstract

The thick sequences of marine clayey deposits that blanket the St. Lawrence Lowlands in south-eastern Canada are highly susceptible to landslides. With 89% of the population of the province of Quebec living in this region, improving our understanding of the mechanisms causing landslides in these sediments is a matter of public security. To accomplish this goal, instruments were deployed at a field site in Sainte-Anne-de-la-Pérade, Quebec, Canada to monitor atmospheric, soil, and groundwater conditions. Field and laboratory measurements of soil geotechnical and hydraulic properties were also performed. Results indicate that the groundwater and pore pressure dynamics at the site cannot be explained using simplified site conceptual models. Further analysis indicates that groundwater dynamics and pore pressures in the massive clay deposits on site are determined by (i) the highly heterogeneous nature of the local geological materials, (ii) the contrasting hydraulic and geotechnical properties of these materials, (iii) the presence of two unconfined aquifers at the site, one surficial and one at depth, and (iv) the presence of the Sainte-Anne River. These results were used to create a new conceptual model that illustrates the complex groundwater flow system present on site and shows the importance of including hydrogeologic context in slope stability analysis.