Contact Erosion at the Interface between Granular Coarse Soil and Various Base Soils under Tangential Flow Condition
Abstract
Under embankment dams and dykes, horizontal groundwater seepage prevails. If the subsoil is layered, and if some coarse layers are not appropriate filters for finer layers, there can be contact erosion at the interface between fine and coarse soils. In order to study contact erosion threshold, some base-soil and coarse-soil combinations were submitted to a flow parallel to the interface between the coarse soil and the base soil. Critical velocities and critical hydraulic gradients were measured for various base soils. Using effective base-soil grain diameter, an empirical expression for critical velocity was proposed that is well adapted for silts or sand/clay mixtures as well as for sands. The mass of eroded soil was measured relative to the flow velocity for each base-soil/coarse-soil setup. The shear stress applied to the interface between base soil and coarse soil was derived from the hydraulic gradient. Using an empirical relationship between applied shear stress and measured eroded mass, erosion rate was estimated for each base-soil/coarse-soil setup.