Landslide on the Toulnustouc River, Quebec

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...