Internal erosion jeopardizes the stability of natural slope and embankments, affected by intricate interactions among hydraulic forces, soil chemistry, and clay mineralogy. This study employed the Pinhole Dispersion Test under varying hydraulic gradients to evaluate dispersive (D), slightly dispersive (SD), and non-dispersive (ND) soils consisting of montmorillonite, illite, vermiculite, and kaolinite. Dispersive (D) soils demonstrated the highest detachment rates (0.0142 ± 0.0015 kg/m 2 /s), which were up to 89 times greater than those of non-dispersive (ND) soils, along with the lowest critical shear stress (τ c = 1.17 Pa) and the highest erodibility coefficients (C e = 1.07 × 10 -3 s/m), signifying "very rapid" internal erosion. Conversely, ND soils required significantly elevated hydraulic thresholds (τ c > 25 Pa) and exhibited “moderately slow” erosion responses. Regression and multivariate analysis identified flow shear stress (τ) as the principal hydraulic driver, whereas sodium adsorption ratio (SAR), exchangeable sodium percentage (ESP), and pH identified as the most significant soil parameters ( r > 0.95, p < 0.05). Soils abundant in montmorillonite and characterized by high sodium adsorption ratios (SAR) had the greatest susceptibility to dispersion, while kaolinite and vermiculite soils, reinforced with divalent cations, displayed enhanced aggregate stability. We derived a power-law model, Dr = 1.05×10 -8 τ 1.362 SAR 3.778 , with R 2 = 0.95 and NSE = 0.95, which shows that SAR intensifies erosion non-linearly. All soils were categorized as internally unstable, yet dispersive soils exhibited a significantly elevated risk of internal erosion, even with low hydraulic gradients. These findings underscore the critical importance of clay mineralogy, dispersion ratio and hydraulic forces in predicting and mitigating erosion risk in geotechnical infrastructure.
Shah et al. (Fri,) studied this question.