Landslides of the Dorset coast: Some unresolved questions

The Dorset Coast includes some of the finest landslides in Britain. They occur at the southern end of the landslide prone strata associated with the Jurassic outcrop. These materials provide many examples where a permeable 'caprock' overlies a clay aquiclude. Because of the structural relationships of these beds along the Dorset coast there is a range of landslide generators each with different properties and styles of failure. This paper describes the individual sites and summarises the existing slate of research. The outstanding problems are then outlined. First, there are many sites and materials which have never received adequate research. Secondly there are technical difficulties. More fundamental, however, are the problems which have only become apparent after intensive study and which must be solved if geotechnical science itself is to advance. These include understanding of the mechanisms of the processes of lateral spreading and ductile clay extrusion, the phenomenon of running sand, geochemical controls of material behaviour and the relationship between pore water pressure, shear strength and landslide movement.