THE MECHANICS OF SMALL TROPICAL FLOWSLIDES IN DOMINICA, WEST-INDIES

Investigation of landslides in the tropical clay soils of Dominica revealed that the debris travelled great distances across low-angle slopes. The initiating mechanism was a shallow rotational or translational slide but the high soil pore water contents invariably led to a flowslide. The tropical clays of Dominica exhibit unusual geotechnical and hydrological properties. The values of residual shear strength exceed what would be expected when comparing them with temperate clays. The soils are more akin to temperate granular materials in their shear strengths. Even allowing for this the pore water pressures need to be close to zero for stability of high-angle slopes. A detailed understanding of run-off processes and subsoil flow is necessary to explain the high flow rates in soils of high water retention capacity. Only rainfalls of exceptionally prolonged high intensity can elevate pore water pressures and induce landslides. There is, therefore, a vast amount of soil water available to form flow slides when movement commences. © 1990.