# Characterization of the Migration of Soil Particles in Lateritic Soils under the Effect of Rainfall
## 1 Introduction  
Slope stability is the ability of a slope to remain stable under its own gravity and external forces. The strength and stability of soil are the key factors affecting slope stability. Internal erosion will change the physical and mechanical properties of soil, which will have an impact on slope stability. Under rainfall infiltration, the internal erosion of the slopebody will lead to changes in the porosity, water content, and pore water pressure of the soil body, which will reduce the strength of the soil body and ultimately lead to instability and damage. When water infiltration erodes soil slopes, fine particles will migrate with water infiltration, and this migration can be categorized into two: fine particles are lost outside the slope with water, and fine particles migrate inside the soil body. Both forms of migration will change the particle distribution of the slope body and thus change the physical properties of the soil body [1]. Among them, for soil pore water pressure, the presence and number of fine particles can significantly affect the pore water pressure [2; 3; 4]. For example, the vertical migration of fine particles in the slope profile affects the change of pore water pressure, and, in some cases, the effect of fine particle migration is more significant than the effects of mass and depth [5]. In addition, the content of fine particles has a significant effect on soil water content, and soil water-holding properties are closely related to particle composition [6], with particles of different sizes responding differently to water. Compared with large particles, small particles have a larger specific surface area, which makes it easier for small particles to absorb water [7], so the higher the relative content of soil fine particles, the higher the water content should be. In addition, the amount of fine particles somewhat changes the strength properties of the soil. For example, parameters such as matrix suction, cohesion, and shear strength of soil increase with increasing clay content [8]. Fine particles absorb water and swell under rainfall, filling the soil pores, reducing the pore space, growing the water flow path, increasing the contact area between the soil and water, and enhancing the viscous effect on water flow, which leads to a decrease in the permeability of the soil [9]. During rainfall, the migration and aggregation of fine particles in the slope body will lead to changes in the particle size distribution of the soil body, which will further affect key parameters such as pore water pressure, water content, and permeability characteristics of the soil body. Therefore, the influence of internal erosion on slope stability is a complex process involving changes in several key parameters such as soil porosity, water content, pore water pressure, and particle distribution. Through an in-depth study of these changes, the mechanism of internal erosion on slope stability can be better understood, providing a scientific basis for slope engineering design and risk assessment. The stability of soil slopes is affected by erosion within the soil body, and this erosion process refers to the transport of fine particles located in the interstices of the coarse particles of the skeleton under the action of seepage. In this case, the coarse particles form the soil skeleton, while the fine particles are free to move in the coarse skeleton under the action of seepage forces [10; 11; 12; 13]. During heavy rainfall, fine particles in the slope flow between gravels, but due to the limitation of pore size, some fine particles will gather in the slope during transportation [14]; others converge to the lower part of the slope and the toe of the slope and ultimately lead to the destruction of the slope [15; 16; 17]. The transport of fine particles will lead to changes in the distribution of soil particles in the slope, which will affect the physical and mechanical properties of the soil and, thus, the stability of the slope.