A Conceptual Framework for Erosion of Unsaturated Cohesive Soil

Abstract Accurately predicting soil erosion remains difficult owing to variability in the factors that drive the interaction of unsaturated flow and soil deformation. For example, seasonal changes in soil moisture affect infiltration, swelling, and soil stiffness, all factors that interact and may affect soil erosion through changes in matric suction, strain, and shear strength. In this study, the effect of changing soil moisture on soil detachment rate and critical shear stress was investigated using erosion tests conducted on statically compacted lean ( n = 7) and fat ( n = 7) clay samples with constant bulk density and degree of saturation ranging from 9% to 98%. Soil detachment rate decreased with increasing soil moisture from 123 to 0.2 cm 3 /(N‐s) and 122 to 0.3 cm 3 /(N‐s) for the lean and fat clay, respectively. Conversely, critical shear stress increased with soil moisture from 0.4 to 3.5 Pa and 0.4–6.1 Pa for the lean and fat clay, respectively. A conceptual framework that links unsaturated cohesive soil erosion to infiltration and soil swelling is utilized to develop regressions for the prediction of the soil detachment rate ( R 2 = 0.90, p‐ value < 6e−7) and critical shear stress ( R 2 = 0.80, p‐ value < 6e−5) from readily obtained measurements of infiltration, swelling, bulk density, shear strength, and moisture content. Implications for predicting soil erosion across landscapes and earthen structures (e.g., earthen dams and levees) are discussed.