The Saint-Jude landslide of 10 May 2010, Quebec, Canada: Investigation and characterization of the landslide and its failure mechanism

Abstract

A landslide occurred on 10 May 2010, along the Salvail River, in the municipality of Saint-Jude, Quebec. Debris of the landslide was formed of clay having horst and graben shapes, typical of spreads in sensitive clays. A detailed investigation was carried out by the Ministère des Transports, de la Mobilité durable et de l'électrification des transports du Québec, in collaboration with Université Laval, with the objective of characterizing this landslide, determining the causes, and learning about its failure mechanism. The soil involved was a firm, grey, sensitive, lightly overconsolidated clay with some silt. Data from piezometers installed near the landslide indicated artesian conditions underneath the Salvail River. Cone penetration tests allowed the location of two failure surface levels: the first one starting 2.5 m below the initial river bed, extending horizontally up to 125 m, and a second one 10 m higher, reaching the backscarp. Investigation of the debris with onsite measurements, light detector and ranging surveys, cone penetration tests, and boreholes allowed a detailed geotechnical and morphological analysis of the debris and reconstitution of the dislocation mechanism of this complex spread.

A case study and implication: particle finite element modelling of the 2010 Saint-Jude sensitive clay landslide

“…1). Leading to death of four people, the landslide had a retrogression distance of 80 m (defined as the distance from the initial crest of the slope to the final stable backscarp) and affected a section about 275 m long, parallel to the Salvail River and a total of 520,000 m 3 soil mass (Locat et al 2017). Both on-site and lab testing was carried out to obtain information on the stratigraphy and the geotechnical properties of the clays.…”

“…The exact cause of the Saint-Jude landslide is unknown. Slope stability analyses were performed in (Locat et al 2017;Locat et al 2011b) along the transect C-C′. In (Locat et al 2011b), it was shown that the initial failure based on drained analysis is very local whereas a large amount of clay would be disturbed if the slope failed under undrained conditions.…”

“…These different failure modes lead to a substantial discrepancy in the factor of safety (FoS) determined under undrained and drained conditions. According to (Locat et al 2017;Locat et al 2011b), the analysis under undrained conditions using the limit equilibrium method provides the FoS of 2.16, whereas the FoS from drained analysis is close to one (more precisely 0.99 with the Bishop method and 1.03 with the Morgenstern-Price method). For detailed slope stability analyses under drained and undrained conditions including the used material parameters, we refer the reader to (Locat et al 2011b).…”

“…2(a)) and then build the entire failure surface by a suitable interpolation. The reader is referred to (Locat et al 2017;Locat et al 2011b) for more details on the obtained CPTU profiles and the procedure to determine failure surfaces. According to the report (Locat et al 2017), the debris of the retrogressive landslide can be divided into four zones (Fig.…”

“…As indicated in (Locat et al 2017), the limit equilibrium method cannot explain the entire event. A better explanation of this geohazard and the associated failure mechanism requires more advanced calculation approaches.…”