## 2 Physical Model Experiments
### Experimental Materials and Plans  
Natural rock-ice avalanches are characterized by a wide variety of particle sizes and irregular, non-fixed shapes. In laboratory experiments, however, ice blocks are typically produced using standardized models, which enhances production efficiency and allows for better control over particle size and shape. To ensure that the particle size difference between the ice and rock fragments does not significantly affect the results, rock fragments are selected to match the size range of the ice blocks. In addition, the influence of the flume's side walls on particle flow and boundary effects is considered. Furthermore, the influence of the side walls of the flume on the particle flow boundary effects should be considered. When the ratio of the flume width to the average particle diameter exceeds 20 times, the impact of the boundary effects on the flow can be considered negligible [29; 30]. In line with these considerations, the ice blocks and rock fragments used in the experiments were prepared as shown in Figure 2. The particle densities were measured using the drainage method. Ice blocks, each with dimensions of 2 cm \(\times\) 2 cm \(\times\) 2 cm, had a density of 920 kg/m\({}^{3}\). The rock fragments, selected for their particle size range of 10-20 mm and average size of 15.8 mm, had a density of 2982.59 kg/m\({}^{3}\) and a total mass of 15 kg. The gravel layer at the flume's base, with a particle size range of 5-10 mm and an average size of 5.9 mm, had a density of 2765.97 kg/m\({}^{3}\) and a mass of 10 kg. Figure 1: Schematic diagram of the physical model test apparatus (Unit: mm). Figure 2: Experimental material schematic diagram: **(a)** the ice cubes are 2 cm\(\times\) 2 cm\(\times\) 2 cm; **(b)** the gravel size is 5–10 mm each; **(c)** the gravel size is 10–20 mm each. The ice content of the rock-ice mixture was controlled by mass percentage. Therefore, prior to each experiment, the two materials needed to be stacked in specific mass ratios according to the experimental conditions. The slope of the upper flume was set at 35\({}^{\circ}\), while that of the lower flume remained at 20\({}^{\circ}\), both of which were maintained consistently throughout the experiments. Drawing on preliminary trials and previous studies on rock-ice avalanches [27], two key factors--ice content and initial deposition configuration--were selected to examine the influence of ice particles on the scraping effect in rock-ice avalanches. The rock-ice mixture was thoroughly mixed, with the initial mass kept constant at 15 kg. Ice content varied from 0% to 100%, with 10% intervals; the 0% (pure gravel) and 100% (pure ice) groups served as controls, resulting in a total of 11 experimental groups. This design allowed for the investigation of ice content's impact on the scraping effect. Three initial deposition configurations were tested: ice on top of rock, rock on top of ice, and a mixed deposition. For each configuration, ice content ranged from 30% to 70%, with 10% increments, to assess the effect of initial deposition arrangement on the scouring behavior. Detailed deposition methods are shown in Figure 3, with experimental conditions provided in Table 2.