Scouring of roadbeds along river highways poses a significant threat to the safety of mountain roads. Relying on the Karakorum Highway (KKH) water damage disaster remediation project, using the erosion function apparatus and theoretical analysis, we studied the scour rate, starting shear stress, and the variation of theoretical model parameters in clay-coarse sand mixed soil samples with different clay contents. We also explored the scour characteristics and damage modes of mixed soils based on the soil skeleton theory. The following conclusions were drawn. As the clay content increases, the starting shear stress of the soil sample rises, scour resistance is strengthened, and the scour characteristics transition from non-cohesive to cohesive soil scour characteristics. The distribution of cohesive fine particles varies from filling the voids between coarse particles to bonding with them, and ultimately separating the coarse particles. The damage mode of the mixed soil samples under scouring water flow varies depending on the filling pattern of coarse particles and clays. The Wilson model exhibits a good fit with the experimental data and can be applied to predict large shear stresses, compensating for the limitations of the over-shear stress model.
