A new model for large landslides in sensitive clay using a fracture mechanics approach

A new model is proposed for the development of large landslides in sensitive clay, and supported by concepts from fracture mechanics. A key assumption in this new model is that the complete failure surface develops before the onset of significant movement, thus predetermining the final extent of failure. The appearance of retrogression is actually the rearward advancing disruption of a monolithic slide mass over a growing zone of liquefied clay. It is seen that the likelihood of propagation of failure, and the resulting occurrence of a large landslide, depend primarily on the brittleness of the sensitive clay. The potential length of shear band propagation is limited by slope geometry, and increases for higher riverbanks and for flatter slopes above the riverbank. The model explains why large landslides in sensitive clay often terminate just adjacent to a reverse break in slope, such as an older landslide crater or a stream gully. The model also indicates that large landslides in sensitive clay could be expected to occur suddenly after a large single perturbation, such as an earthquake, or after a seemingly innocuous small trigger following the accumulation of a large number of annual load cycles, as observed frequently in nature.