Numerical investigation of internal erosion initiation using CFD model in hole erosion testing

Abstract Internal erosion happens when fine soil particles get detached and carried away by seepage flow inside hydraulic structures, which can eventually cause damage or failure. In this study, we investigate erosion initiation via a two-dimensional Hole Erosion Test (HET) coupled with CFD modeling. Three compacted soil samples with clay contents of 78.32% (Vertisol), 42.22% (Calcimagnesic soil), and 12.88% (Fersialitic soil) were subjected to inlet pressures of 3 500 Pa, 4 500 Pa, and 6 000 Pa. CFD results show that erosion begins once the local wall shear stress exceeds each soil’s critical threshold ( $${\uptau}_{\text{c}}$$ ): 8.5 Pa for the high-clay Vertisol, 7.0 Pa for the mid-clay Calcimagnesic soil, and 5.5 Pa for the low-clay Fersialitic soil. The corresponding erosion coefficients (kₑ) are 3.5 × 10⁻ 4 , 5.5 × 10⁻ 4 , and 7.0 × 10⁻ 4 m 2 ·s· $${\text{k}\text{g}}^{-1}$$ . Under the same hydraulic loading, the high-clay soil exhibited the lowest erosion rate, while the low-clay soil eroded most rapidly. These results quantify the strong link between clay content, critical shear stress, and erosion rate, underscoring the importance of soil cohesion in controlling internal erosion and highlighting the influence of clay content and hydraulic loading on erosion behavior under controlled HET-like conditions.