The energy reduction factor (FER) to model sensitive clay flowslides using in situ geotechnical and rheological data

Sensitive clays, mostly found in Eastern Canada and Scandinavia, are prone to various types of landslides; among them are flowslides that may affect hectares of land. Debris from those slides has high mobility, with runout distances that may extend over hundreds of meters in relatively flat and non-channelized terrain. Most studies on the mobility use apparent rheological properties to back-calculate the runout behavior of these landslides. This works well for back-analyses of landslides but is of little help in a context of hazard mapping, where prospective analysis of future landslides is necessary. In this study, a new factor, using the destructuration index concept, is introduced to estimate the remaining energy available as kinetic energy for runout after the remolding of the sensitive clay: the energy reduction factor (F-ER). Using the F-ER allows the use of real rheological data acquired with a rheometer to analyze the post-failure behavior of a flowslide in sensitive clays. This method is applied on a sensitive clay landslide which took place in Quebec and where rheological and geotechnical data are available.