Factors relating to the landslide process in Canadian quickclays

The formation of. and landsliding in extremely sensitive postglacial clay soils (quickclays). could be affected by certain factors including mineralogical composition, interparticle bond type, soil structure, leaching, cementation and particle coatings. Factors which should be taken into account during related investigations include nomenclature and size limits, model soils, distribution, rheology, scientific status, local earthquake intensity and frequency. Landsliding in quickclays occurs largely by means of catastrophic flowslides. These are due to the predominance of short range bonds in the soil system. The short range bonds ensure a very low plasticity index (of the order of 10 or below) and may be due to the inherent nature of the material or to post‐depositional events. Mineralogical studies suggest that the former is more critical although cementation plays a major role in Canadian quickclays. The Yatsu philosophy of material investigation should be applied to quickclays on a larger scale: landsliding and slope evolution are ultimately controlled by the forces operating (or not operating) between two adjacent soil particles. A particular set of tectonic, glacial and sedimentological circumstances are required for quickclay formation; the correct combination rarely occurs which accounts for the very limited occurrence of clay soils with sensitivities of greater than 100.