Canadian Geotechnical Colloquium: understanding spreads in Canadian sensitive clays

Spreads are one type of large landslide occurring in Canadian sensitive clays. They are characterized by the rapid spreading of clay blocks, having horst and graben shapes, moving on a layer of remoulded clay. Spreads cover large areas, develop rapidly, and conventional stability analyses do not apply. Université Laval, Ministère des Transports et de la Mobilité durable, and Ministère de la Sécurité publique du Québec have worked together to answer the following question: what are the geotechnical and morphological parameters controlling initiation, propagation, and extent of these spreads? This paper portrays the advancement of the research program put in place by integrating field investigation, laboratory testing, and numerical modelling. It presents the state of the art of our understanding of spreads in Canadian sensitive clays, focusing on characteristics of spreads in Canadian sensitive clays; analysis of the failure mechanism of spreads; and the geotechnical properties of soils involved in these landslides. Although it focuses on sensitive clays, the work presented has applications to other materials presenting a strain-softening behaviour, such as rock and snow.