Failure mechanisms of landslide dams with different materials: laboratory experiment and physical analysis

China's southwestern region is characterized by active geological structures and frequent seismic activities. These conditions frequently trigger landslides that obstruct rivers and form landslide dams. The failure of these dams represents a significant threat to downstream populations, as exemplified by the breach of the Tangjiashan landslide dam with the Wenchuan earthquake. This study focuses on the overtopping breach type of landslide dams. It conducts large-scale experiments to investigate the impact of various grading materials on the breach process. Furthermore, the DABA (Dam Breach Analysis) numerical simulation model is employed to conduct an in-depth analysis of the breach process in landslide dams. Based on the experimental and simulated results, the following characteristics of landslide dam breaches were analyzed. Under identical inflowing conditions, the peak discharge of the fine-grained dam is 1.6 times that of the widely-graded dam, which has the significantly higher susceptibility to breaching. Although both dams failed due to overtopping, their erosion mechanisms differed substantially. For the widely-graded dam, coarse particles led to scouring and retrogressive erosion, significantly prolonging the breaching process. In contrast, the fine-grained dam primarily failed through layered scouring. The results show a high degree of consistency between the DABA numerical simulation outcomes and the large-scale experiment data, thus validating the model's reliability. The parameter sensitivity analysis revealed that breach development duration and peak discharge were significantly influenced by dam height, dam crest width, and initial water level. Scientific simulation models can more precisely predict the breach time and impact range of landslide dams, aiding in the development of more effective prevention methods. • Although both widely-graded dams and fine-grained dams fail due to overtopping, their failure mechanisms exhibit significant differences. • The peak flow generated by the breach of fine-grained dams is substantially higher than that of widely-graded dams, with greater flow velocities. This results in higher hazard potential and shorter disaster response times. • The computational results of the DABA model demonstrate close alignment with experimental scenarios, robustly validating the model’s reliability and computational efficiency.