## 6 Comparative Analysis and Discussion  
According to the overtopping numerical tests of the above three different model schemes, the change law of the model breach width using fine tailings mixed with 5% fly ash is more similar to that of the prototype tailings dam with the breach width reaching the maximum almost at the same time. The breach width of the model using fly ash mixed with bentonite (4:1) increases obviously, and the breach width of this scheme reaches the maximum earlier, which indicates faster erosion. When the prototype tailings are used as the model dam material, the dam-break process shows obvious hysteresis. Even when the time reaches 6000 s, the breach width still does not reach a reasonable size. According to the development law of breach depth, the scheme of fine tailings mixed with 5% fly ash is most similar to the prototype of tailings dam. The breach depth of the scheme of fly ash mixed with bentonite (4:1) shows great fluctuation with the change of time. In the vicinity of 3700 s, it even decreases instead of increasing. Excluding the influence of test contingency, it may be that under the erosion of sediment, the breach deepens, causing the instability and collapse of the slopes on both sides of the breach. This process can reduce the depth of the breach temporarily. The prototype tailings scheme shows more obvious hysteresis of the dam break. In addition, by observing the dam failure characteristics of each scheme, the tailings in the scheme of fly ash mixed with bentonite (4:1) show great mutual displacement, and a large amount of sediment is deposited in the downstream, and the dam failure characteristics are inconsistent with the prototype of the tailings pond. In the prototype tailings scheme, the dam-break speed is obviously slower than that of the prototype tailings pond, and the downstream deposition is larger, which is inconsistent with the prototype tailings pond.  
The change law of the breach width and breach depth of the tailings dam with time in the prototype as well as three model schemes is shown in Figure 13. When the breach extends to the dam crest, then the tailings dam is considered to have undergone whole failure. The time interval needed for the tailings dam failure in each scheme can be measured as shown in Table 5. The predicted dam failure time of the model using fine tailings mixed with 5% fly ash is the closest to the dam-break time of the prototype tailings dam, and the dam-break time of the scheme of fly ash mixed with bentonite (4:1) is also relatively close but slightly longer. However, the longest predicted dam failure time by the model scheme using prototype tailings is about 7500 s, which is very different from that of the prototype. Based on the breach process and dam-break time, the reduced model scheme using 5% fly ash mixed with fine tailings can better meet the overtopping failure characteristics of the prototype tailings dam. Above all, the similarity between the overtopping dam-break model and the prototype can be greatly improved by using inception similarity optimization to select the model sand.  
Figure 12: Dam-break process of tailings pond prototype sand scheme.  
Figure 13: Comparison of model scheme and tailings dam prototype breakage development characteristics.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Name** & \begin{tabular}{c} **Fly Ash Mixed with** \\ **Bentonite (4:1)** \\ \end{tabular} & \begin{tabular}{c} **Fine Tailings Containing** \\ **Mixed with 5\% Fly Ash** \\ \end{tabular} & \
\begin{tabular}{c} **Prototype Tailings** \\ **Prototype** \\ \end{tabular} &
\begin{tabular}{c} **Tailings Dam** \\ **Prototype** \\ \end{tabular} \\ \hline Time (s) & 6300 & 5800 & 7500 & 5700 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Comparison of dam-break time.