## 3 Numerical Test Method and Scheme Design  
_Numerical Calculation Method_  
In order to verify the similarity of the model overtopping process by selecting the model tailings dam material with optimized incipient velocity, numerical tests were carried out taking a tailings dam in southern China as prototype. The FLOW-3D software is used for modeling and analysis of the numerical experiment. According to the design scheme of the prototype tailings dam, the prototype tailings dam is 26 m high and 770 m long. The downstream slope ratio of the dam is about 1:5, and the slope ratio inside the tailings pond is about 1:100 (Figure 2). A small opening is made at the top of the dam to predetermine the point of overtopping. When overtopping occurs, the overtopping water flow scours the tailings dam continuously under the action of gravity, and the tailings on the dam body begins to start and move together with the waterflow when the overtopping flow reaches a certain velocity. To better observe the dam-break process and better judge the discharge of tailings as well as the change of upstream water level, the upstream and downstream areas of the dam should be included in the establishment of the numerical model. According to the actual size of the prototype tailings dam and in combination with the scale of the indoor model test, the width of 40 m of the prototype tailings dam is intercepted for numerical testing to observe the dam-break characteristics of the prototype tailings pond. Therefore, a prototype analysis area with a value range of 260 m \(\times\) 40 m \(\times\) 26 m is established (Figure 3). When considering the overtopping, the water head height in the reservoir should be greater than the elevation of the dam crest, and the inflow can be added to the calculation area by setting the pressure boundary. However, considering the pressure boundary condition, the inflow water has a certain initial water pressure, which will produce a certain initial pressure on the reservoir water, resulting in too fast fluid velocity when the dam fails, and the dam scour is quite different from the actual situation. In order to solve the influence of the initial pressure caused by the pressure boundary on the experimental results, a baffle is set behind the water area in the reservoir to block the pressurized water. After the water overflows the baffle, it flows into the water area in the reservoir. At this time, the initial pressure caused by the pressure boundary is effectively buffered. Therefore, it can well simulate the water level rise in the reservoir caused by precipitation and mountain torrents, and the overtopping dam break due to the water body under the action of gravity. To achieve better calculation convergence, the grid of this model is selected to be equal in length, width and height; that is, the calculation element is set as a cube element. FAVOR is a method that incorporates geometric effects into the governing equations [23]. The FAVOR technique uses the solid volume fraction in each grid to determine the surface of the solid, establish the control fluid and make the grid geometry completely independent (Figure 4). Using FAVOR technology in dam-break simulation, the sediment volume fraction parameters in the grid can be calculated accurately, so that the form and state of dam failure can be described accurately. In the numerical simulation, the sediment is controlled by the equation of motion. The purpose of dividing the grid is to discretize the relevant area of tailings dam break, so that the motion equation can be calculated and solved on the discretized grid. Compared with the traditional mesh processing technology, FAVOR shows higher efficiency of the operation. The mesh processed by the FAVOR  
Figure 3: Dam-break calculation model and mesh division. Figure 2: Schematic diagram of the prototype tailings dam. method not only simulates the solid boundary well but also uses fewer meshes, which would greatly improve the efficiency of the operation.