Influence of inter particle force and flow velocity on the motion of clay particles during soil erosion

Clay particle movement during soil erosion is jointly controlled by macroscopic hydrodynamic and microscopic interparticle forces (electrostatic repulsion, van der Waals forces, and hydration repulsion); however, the microscopic mechanical mechanisms remain unclear. This study established a visual microfluidic experimental platform, adjusting interparticle forces by controlling the electrolyte concentration, and combined it with a high-speed photography system to investigate the effects of fluid velocity and interparticle forces on clay particle separation, migration, and collision-adhesion behavior. The results indicated that an increase in the net repulsive force between the particles significantly weakens soil erosion resistance. The critical threshold for the net repulsive force at a particle spacing of 2 nm was 5.72 atm. Beyond this threshold, the proportion of particles with a diameter of less than 20 μm released from the breakdown of clay aggregates exceeds 70 %. Moreover, the erosion rates increase by more than sevenfold, and the proportion of individual transported particles sharply increases. Below this threshold, attractive forces dominate, particles tend to aggregate, and erosion occurs primarily through block detachment, resulting in lower erosion rates. Increasing the flow velocity significantly amplifies erosion rates; a 10-fold increase in flow velocity results in a 7.5–13-fold increase in erosion rates. Additionally, the flow velocity governs the particle collision frequency. Overall, the flow velocity and particle–particle repulsive forces synergistically drive erosion; however, flow velocity’s contribution is dominant. This study quantitatively revealed the erosion mechanism driven by flow velocity dominance and interparticle force synergy, providing new insights into the microscopic mechanics of clay erosion.