SPREADS IN SENSITIVE CLAYS IN QUEBEC PROVINCE: A SYNTHESIS OF 14 HISTORICAL CASES

In the sensitive clays of the Quebec Province, a large landslide of more than one hectare in area occurs on average every two years. Based on an historical inventory of landslides in the sensitive marine clays of Québec since 1840, which is currently underway at the Quebec Ministry of Transportation (MTQ), these large landslides can be classified mainly in two types based on their failure and post-failure mechanisms and characteristics, namely flowslides and spreads. The latter were poorly documented, but they have been widely studied since the early 2000s, in numerous collaborations between Laval University and the MTQ. This communication summarizes a very detailed compilation of 14 cases of spreads in sensitive clays in the Québec Province. This synthesis includes the description of some of the characteristics of pre-failure, failure and post-failure stages, based on geometric, geomorphological and geotechnical properties. Analysis of the data shows that spreads occur in a wider range of geotechnical properties than flowslides and that it can occur on gentle slopes of relatively low heights. This summary highlights the difficulty of identifying specific conditions predisposing to this kind of large landslide.