ABSTRACT
A classification of landslide causitive processes is proposed in terms of external effects that result in increased shear stresses within the potential landslide mass, and internal effects that result in decreased shear strengths. These processes are reviewed in the context of stiff clays, with particular reference to the internal effects.
The more important causes of strength loss within slopes are due to either (1) decreasing effective stresses or (2) reduction in the soil strength parameters (c′, ϕ′ of the slope material. Processes leading to (1) include post-erosion swelling and rising groundwater within the slope, whereas those leading to (2) include weathering, shear-rate effects, and progressive failure.
The relation between laboratory measured strengths and strengths inferred from landslide stability analyses is discussed, and it is concluded that for low-plasticity clays the agreement between the two strengths is close. For plastic clays it is suggested that slope processes (perhaps particularly progressive failure) reduce the field strength well below that measured in the laboratory.
