Grain size dependent rheology on the mobility of debris flows

When dealing with natural geo-hazards it is important to understand the influence of flow characteristics on the submarine landslides, because the flow characteristics of fine-grained soils are most likely governed by the rheological properties. It may further relate to the mobility analysis of debris flow. Geotechnical and rheological investigation on the clay-rich materials were compared with those of silt-rich materials. For the examined fine-grained soils, the flow behavior depends on the volumetric concentration of solid and surface phenomenon, particularly for non-swelling materials. Assuming that the debris flow materials behave as the Bingham fluid, a possible relationship between geotechnical and rheological properties are proposed. From an empirical relationship between yield stress and plastic viscosity, a comparison emphasizes the grain size effect on the rheology of geomaterials encountered in various environments. The larger the particle size involved in the matrix, the lower the value of viscosity which is in the order of 10 times. Debris flow mobility with respect to rheology concerning the large particle size is emphasized.