The September 5, 1987, landslide on the La Grande River, James Bay, Quebec, Canada

• Published in: Canadian Geotechnical Journal
• Main Authors: Lefebvre, Guy, Rosenberg, Peter, Paquette, Jean, Lavallée, J. G.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1991
• Subjects: Civil and Structural Engineering; Geotechnical Engineering and Engineering Geology; Canada; La Grande River; James Bay
• Online Access: http://dx.doi.org/10.1139/t91-032; http://www.nrcresearchpress.com/doi/pdf/10.1139/t91-032

The September 5, 1987, landslide at kilometre 82.5 on La Grande River affected a slope about 60 m high inclined at about 35°. The site had been identified as presenting high risks of a major landslide and had been under observation for several years. The conditions existing before the landslide are relatively well documented from a deep boring put down in 1975 at the slide location and from prior observations and photographs of the river bank erosion. The overburden deposit, sand at the ground surface changing to a silty clay at depth, was normally consolidated but affected by a strong underdrainage. Stability analyses confirm the strong underdrainage deduced from the 1975 piezometric reading. The slide retrogressed 290 m from the river on a surface inclined at 6°. The location of the retrogression surface appears related to the undrained shear strength profile. Key words: landslide, earthflow, sensitive clay, groundwater, river erosion, slope stability.