Loess disaster chains on the Heifangtai Platform, China, cause frequent loess landslides and form landslide dams, thus obstructing rivers. In addition, the failure of landslide dams causes loess mudflows and other related disasters. In this study, the influences of different inflow rates on the failure process and triggering mechanisms of loess landslide dams were explored using five sets of model experiments. These experimental results revealed that the failure of loess landslide dams occurs through overtopping and piping failure, or overtopping failure. Overtopping and piping failure can be divided into infiltration, seepage channel development, break overflow, and rebalancing. When the inflow rate was 1.0 L/s, the water could not penetrate the dam in time. Overtopping failure primarily involves horizontal and downward erosion of the breach. The inflow rate was positively correlated with soil transport, peak flow velocity, and peak bulk density based on the experimental data. The bulk density of the failure mudflow was categorized into slow increase, transition, and attenuation stages based on our experimental results. In addition, by analyzing the volume and stability of residual dams, the likelihood and damage degree of secondary hazards after the dam failure were initially explored. This study provides a scientific basis for relevant studies on loess landslide dam failure.

The difference in soil properties determines the different breaching characteristics exhibited by landslide dams (LDs) and debris-flow dams (DFDs). In this study, two types of soil were prepared by controlling the initial water content and the mixing time of the soil to construct the LD and DFD. Based on observations of breach in dams with six different grain size distributions, the following conclusions were drawn: (1) the erosion resistance within the soil leads to a slower failure speed for DFD under the same grain size distribution and particle density. However, both types of dams exhibit a nonuniform downcutting process in the longitudinal direction, induced by uneven velocities. (2) Laterally, DFDs are characterized by the creep slide of the breach bank, distinct from the intermittent slide observed in LD. (3) For the range of conditions tested, the peak discharge of LD significantly exceeds that of DFD. Additionally, the flood curve of LD exhibits a bimodal characteristic, attributed to the slide of the bank slope and the nonuniform distribution of particles within the dam. Finally, a prediction formula for the downcutting coefficient of the breach was established and validated by past studies. This study provides a basis for predicting outburst floods of LD and DFD.