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

Alexandra Germain, Nathan Young, Jean-Michel Lemieux, Ariane Locat, Hugo Delottier, Philippe Fortier, Serge Leroueil, Pascal Locat, Denis Demers, Jacques Locat, Catherine Cloutier

Dans les comptes rendus d’articles de la conférence: GeoNiagara 2021: 74th Canadian Geotechnical Conference; 14th joint with IAH-CNC

ABSTRACT: The St-Lawrence Valley is characterized by thick post-glacial marine clay deposits that are highly susceptible to landslides. Since 89% of the population of the Province of Quebec lives in this region, our understanding of the mechanisms causing landslides in these sediments must be improved to help reduce their impact and protect the population. To achieve this goal, a study site located in Sainte-Anne-de-la-Perade, Quebec, Canada, was instrumented in order to obtain high-resolution spatial and temporal meteorological, geotechnical and hydrogeological data. Field and laboratory measurements of soil geotechnical and hydraulic properties were also performed. Data indicate 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 data were then used to create a conceptual model in order to better understand the groundwater and pore pressure dynamics at the study site. The resulting conceptual model was significantly different than the simplified site conceptual models that are usually used in geotechnical studies in massive clay deposits. Since the hydrogeology of massive clay deposits is typically conceptualized as a 1-D flow system occurring in a homogenous formation, these results show the importance of including local hydrogeological context in slope stability analysis.

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