Conference Dates

June 18-21, 2006


Soft sensitive clays like quick clays are well known in Scandinavia and in some regions in Canada. The salt pore water of these marine clays has been leached out since last glaciations and left a brittle mineral structure. Slides in quick clays can be extremely disastrous, as in Verdal, Norway in 1893 or Rissa in 1978. The slides may be initiated by local overloading, river erosion or similar and can escalate in size in a retrogressive manner in which large volumes of clay finally may liquefy. Norwegian quick clay has a very low permeability and hence pore water pressure becomes a crucial parameter that can affect the stability of material. Failure in quick clay (with a post-peak strain softening behavior) is often associated with the development of shear bands, i.e. narrow zones of localized deformation, and the failure loads depend on the thickness of these shear bands. Plane strain compression tests were performed, at laboratory 3S, Grenoble France, to observe the formation and propagation of shear bands during undrained shearing. Biaxial plane strain tests were performed in quick clay having different sensitivity and local pore pressure variation throughout the test was monitored. Image analysis is done to detect shear band thickness and mode of failure. Further, usefulness of shear band analyses in landslide calculation using finite elements and consequence of such failure is also discussed numerically. A stability analysis of a quick clay slope is made to illustrate the progressive failure mechanism.