Experimental study on erosion mechanisms in landslide dam breaching: effects of particle composition

Abstract

Landslide dam breaching, primarily driven by overtopping erosion, can trigger catastrophic outburst floods, posing significant risks to downstream areas. Understanding the erosion mechanisms underlying dam failure is crucial for improving flood risk assessment and disaster management. This study conducted nine flume experiments on landslide dam failure, systematically varying four key factors: median particle size (D₅₀), uniformity coefficient (C_u), fine particle content (F_f), and coarse particle content (F_c). Results indicate that the failure process consists of two distinct stages: headward erosion and overall erosion, with knickpoint migration serving as a key indicator. The breaching process and hydrographs are significantly influenced by D₅₀, C_u, and F_c, whereas the impact of F_f is relatively minor. Bed shear stress exhibits a strong correlation with erosion rates (R² = 0.73), outperforming flow power and unit flow power. The critical shear stress model provides more accurate predictions, with critical shear stress (τ_c) strongly correlated with C_u (R² = 0.975) and influenced by F_c, while the coefficient of erodibility (K_d) is primarily determined by F_f with minimal impact from C_u (R² = 0.005). Experimental observations further identify two distinct breach morphology evolution modes: uniform and non-uniform surface erosion, governed by the interplay between flow shear stress and soil erosion resistance along the flow direction. Flow shear stress initially increases before decreasing, while apparent erosion resistance gradually rises due to increasing sediment concentration. This study enhances the understanding of how particle composition affects landslide dam breaching, offering a framework for improving predictive models and flood hazard mitigation strategies.