# Characterization of the Migration of Soil Particles in Lateritic Soils under the Effect of Rainfall
## 2 Research Background and Experimental Design
### Experimental Design
#### 2.3.3. Experimental Program and Data Acquisition  
1. Rainfall intensity and duration  
During the rainy season from June to September in the mountainous areas of Sichuan, China, the maximum rainfall intensity always exceeds 100 mm/h, which is the main reason for the formation of geologic disasters such as mudslides and landslides [15; 25]. Therefore, we studied the migration characteristics of laterite fine particles under different rainfall intensities. In order to make the rainfall erosion phenomenon more obvious, we selected three rainfall intensities of high, medium, and low to carry out internal erosion simulation experiments, respectively, at 50 mm/h, 100 mm/h, and 150 mm/h. Combined with our experiments, it was found that when the rainfall intensity was 150 mm/h and the rainfall duration was 40 min. This would be very difficult with the phenomenon of a large number of fine particles aggregated within the slope, indicating that, at this time, the internal seepage of the slope is stabilized, and the fine particles have been basically lost. Therefore, in this study, a rainfall duration of 40 min and rainfall intensities of 50 mm/h, 100 mm/h, and 150 mm/h were set to investigate the migration of soil particles. 2. Sand transport rate, pore water pressure, and water content  
In order to obtain the variation of pore water pressure and volumetric water content with rainfall calendar time under different rainfall intensities. Before the experiment, the pore water pressure and water content sensors were buried in a fixed-shape soil pile, as shown in Figure 5, and the rainfall equipment was activated after turning on the pore water pressure and water content collector. Secondly, in this study, to obtain the slope surface runoff and internal seepage obtained at the toe of the slope under different rainfall intensities, the slope surface runoff and internal seepage slurry were collected during the simulated rainfall period, and the rainfall was collected every 2 min after the start of rainfall; each time, it was collected for 20 S. A total of 20 times were collected, taking into consideration of the hysteresis of the internal seepage, so the slope surface runoff was collected first and then the internal seepage slurry was collected. Rainfall was stopped after  
Figure 6: The distribution of fine particle content in the initial state of the slope. 40 min and closed after 41.5 min, and the rainfall was stopped after 41.5 min. The pore water pressure and water content equipment were turned off after 41.5 min. The collected slurry was weighed, settled, and separated from the soil particles. The mass of soil particles carried by one milliliter of slurry per minute was converted to the sand transport rate for slope runoff and internal seepage. 3. Spatial variation in the value of the parameter \(\mu\)  
In order to obtain the soil scale distribution parameter, it is necessary to sample the soil after the end of rainfall, and in order to establish the spatial variation of the parameter \(\mu\)-value, it is necessary to sample the soil with different rainfall intensities and rainfall calendar times. Therefore, in this paper, the spatial distribution of \(\mu\)-values of soil at four rainfall moments, 10 min, 20 min, 30 min, and 40 min, is chosen to show the migration of fine particles. Because sampling causes damage to the slope and affects the transport of fine particles in the slope in subsequent rainfall, the experiments with rainfall durations of 10 min, 20 min, 30 min, and 40 min were conducted separately for the same rainfall intensity, with special attention to the fact that, except for the experiment with a 40 min rainfall duration, the experiments with the other durations were sampled only at the end of the rainfall, and the data on the sand transport rate, pore water pressure, and water content were not collected. The data on sand transport rate, pore water pressure, and water content were not collected.