# Similarity Model Test on Rainfall Scouring Mechanism of High-Speed Railway Subgrade Slope
## 4 Conclusions  
Based on the indoor large-scale rainfall scouring erosion model test, this paper conducted a qualitative and quantitative study on the scouring erosion on the high-speed railway subgrade slope. The main conclusions are as follows:  
During rainfall scouring, the smaller the particle size, the earlier the scouring erosion occurs. In addition, soil particles on the slope bottom were scoured more severely than those on the slope upper. With the increase in rainfall intensity or rainfall time, sheet erosion developed into more pits, and the depth and diameter of the pits gradually increased and evolved into gully erosion. The incipient flow velocity formula of coarse-grained soil is verified by the model test result. Most of the TR is larger than the ER, and Equation (1) can play an early warning role in slope anti-scouring stability with safety. With the increase in rainfall intensity, slope gradient, and the change in soil particle gradation (removing R1), the incipient velocity of soil particles on the slope will be reduced. The rainfall intensity increased from 0.5 mm/min to 1.5 mm/min, and the hydraulic radius  
Figure 17: Waterlogging time of G1–G5. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Groups**} & **Rainfall Intensity** & **Max Flow Velocity** & **Particle Size** & **Max Percent of Eroded** \\  & **(mm/min)** & **(cm/s)** & **(mm)** & **Particles (\%)** \\ \hline G1 & 0.5 & 13.12 & 1.71 & 27.92 \\ G2 & 1.0 & 17.94 & 4.89 & 49.48 \\ G3 & 1.5 & 21.34 & 8.13 & 85.04 \\ G4 & 1.0 & 15.65 & 4.71 & 58.84 \\ G5 & 1.0 & 17.61 & 10 & 100 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Scouring situation of each group. decreased due to rapid slope saturation and difficulty in maintaining ponding, resulting in a reduction in the soil particle incipient velocity of up to 20%. When the slope increases from 1:1.5 to 1:1.25, the drag force on the soil particles along the slope direction increases and the hydraulic radius decreases, resulting in a decrease in the incipient flow velocity of about 20%. The removal of the smallest particle size soil particles, and the reduction in the shear strength of the slope soil makes soil particles easier to scour and start, and the incipient flow velocity decreases by about 16%. Combined with the relationship between slope velocity and rainfall intensity, the rainfall intensity curve varied with the incipient particle size. Under different slope gradients, rainfall intensity and soil particle gradation are established, which can reflect the particle size range of the scouring erosion threshold on the slope surface under various rainfall intensities. With the increase in rainfall intensity, the soil particle size range of the erosion threshold on the slope becomes larger, which provides the basis for slope erosion stability analysis and protection design. Conceptualization, S.-W.W., J.-J.J. and S.L. ; methodology, J.-J.J. and S.L. ; software, J.-J.J. and Z.-D.C.; validation, J.-J.J. and S.L. ; formal analysis, S.-W.W., J.-J.J. and S.L. ; investigation, S.-W.W., J.-J.J. and Z.-D.C.; data curation, S.-W.W., J.-J.J. and Z.-D.C.; writing--original draft preparation, J.-J.J. and Z.-D.C.; writing--review and editing, J.-J.J. and Z.-D.C.; visualization, J.-J.J., S.-W.W. and S.L. ; supervision, D.-G.C., S.-W.W., S.L. and Z.-D.C.; project administration, S.-W.W., J.-J.J. and Z.-D.C.; funding acquisition, D.-G.C., S.-W.W. and Z.-D.C.; resources, D.-G.C. All authors have read and agreed to the published version of the manuscript. This work was supported by the Scientific Research Project of China Academy of Railway Sciences Co., Ltd. (2021 YJ083). The funder had the following involvement with the study: determination of testing site, water and electricity supply. Not applicable. The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy. Author [PERSON], [PERSON] and [PERSON] were employed by the company China Academy of Railway Sciences Corporation Limited.