Landslide on the Toulnustouc River, Quebec

Abstract

A landslide in a very stiff beat extra-sensitive (or quick) deposit of fine-grained estuarine sediments involved approximately five million cubic yards of soil. The overall instability is attributed to a mechanism of progressive failure. It is reasoned that the propagation of a failure surface and the development of a failure scarp all occurred while the landslide mass remained intact. The whole mass then moved down and out, completely blocking the Toulnustouc River within a few minutes.The particularly high strength of the Toulnustouc estuarine sediments, with natural undrained shear strength values of the order of 8000 lb./sq.ft., together with a remoulded consistency of a viscous liquid, offered a somewhat unique opportunity to study the mechanical behaviour of the structure of a sensitive soil. On the basis of the test results, the concept of an “open, cementation-bonded structure” is developed. This concept is used not only to understand the behaviour of the laboratory samples, but also to understand the mechanism of the landslide. It is believed that this conceit of soil structure may be applicable to all sensitive Canadian marine and estuarine clays.