Effects of fines content and stress history on surface erosion of cohesive soils

Surface erosion involves the removal of soil from ground surfaces, riverbeds, or seabeds by flows or currents. While internal erosion has been widely researched, surface erosion—especially in cohesive soil—remains less explored from a geotechnical perspective. This study examines effects of fines content and stress history on the erodibility of cohesive soils. Using five materials with varying fines contents, key erosion parameters, including erosion coefficient ( K d ) and critical shear stress ( τ c ), were measured in a purpose-built apparatus. The results were correlated with the shear strength under zero normal stress ( τ d s ) obtained from a modified direct shear test. It was found that while τ c showed a strong correlation with τ d s in soils with varying fines contents, this correlation weakened under stress history effects. In contrast, the correlation between K d and τ d s remained more consistent for varying fines contents and stress history conditions. Notably, higher fines content did not always enhance erosion resistance, and excessive fines could reduce the erosion resistance. Increasing OCR improved the erosion resistance, with the most notable changes occurring at OCR ≤ 4. Moreover, the stress history effects on soil erodibility were visualized by linking the erosion coefficient to the void index.