Characterization and post-failure analysis of the 1980 landslide in sensitive clays at Havre-St-Pierre, Québec, Canada

Abstract

Early in the morning of April 3rd, 1980, approximately 1.15 × 106 m3 of soils from the coastal bluffs spread out over the tidal flat along the North Shore of the Jacques-Cartier Strait in the Gulf of St. Lawrence. This landslide had a width of 410 m and had retrogressed back up to 110 m from the slope crest, cutting through Highway 138, 9 km west of the town of Havre-St-Pierre. In this area, the coastal bluffs are approximately 23 m high and consist, from the bottom to the top, of a thick marine sensitive clay unit from the Goldthwait Sea, overlain by 3 m of sand and 3 m of peat on top. The debris morphology has a “thumbprint-like pattern” characterized by unbroken blocks of intact clay forming elongated ridges, surrounded by a mixture of remoulded clay, sand and peat, aligned parallel to the bluff and arched in the direction of the flow. The absence of obstacles and the non-channeled character of the flow path of the Havre-St-Pierre landslide provide a good opportunity to characterize and analyze the post-failure stage of this large landslide in sensitive clays.