Flowsliding in Sensitive Soils

Abstract

The susceptibility of sensitive soils to large flowslides is a serious geotechnical problem. Scientific study of this natural phenomenon is necessary if future losses of life and property are to be avoided. Rational methods of flowslide terrain evaluation are required for project planning and development.Published information on 41 documented landslides was supplemented by air photo studies, field studies, and data from a variety of soils reports in order to compare the characteristics of flowslide terrain with more stable terrain that was equally well dissected by river valleys. The phenomenon of flowsliding was also considered from an analytical approach. These studies indicate that landslides in sensitive soils can be generally classified as simple rotational slips, retrogressive rotational flowsliding, or earthflows. An earthflow involves undrained extrusion of sensitive soils and is a continuous flow process that occurs only when the stability number, Ns = γH/Cu, for the material in the slope exceeds the number 6 within the depth of potential flow.A general relationship was found to exist between the stability number, Ns, and the distance of retrogression although secondary factors such as sensitivity, stratigraphy, topography, and the presence of materials susceptible to liquefaction appear to vary the limits of flowsliding.