## 1 Introduction  
Landslides refer to the geological phenomenon of rock and soil mass sliding along a slope, these are a type of natural hazard that is widely distributed throughout the world [1, 2]. Landslides cause tens of billions of dollars of economic losses and serious casualties worldwide every year [3]. In areas with complex geological conditions, landslides occur more frequently [4, 5, 6, 7]. In mountain regions, landslides are often triggered by intensive rainfall [8, 9]. Rainfall and infiltration enhance moisture content, which further decreases the matrix suction and soil shear strength [10, 11]. Rainfall characteristics are often used as criteria for landslide occurrence [12, 13]. The rainfall's intensity and pattern influence the characteristics of landslides [14, 15, 16]. To date, there have been many studies on the effects of rainfall on landslides. Research methods include in situ experiments, laboratory experiments, and numerical simulations [17, 18]. The artificial rainfall test is an effective method when used to study rainfall-induced landslides [19]. Slopes with different soil compositions respond differently to rainfall. Fine particle migration leads to pore blockage [20] and the soil composition of slopes is closely related to their landslide susceptibility. Research has showed that a prerequisite for landslides to occur is that the clay percentage of the soil is higher than 2.5% [21]. The soils in a region where earthquakes happen often have many coarse particles, such as gravel. The proportion of gravel in soils has a great influence on the density and void ratio, which determines the timing and type of landslides [22]. The failure mode is closely related to the grain size [23]. The type of landslide is usually a gully failure when small gravel content is present and usually a \"layer-by-layer sliding\" failure when large gravel content is present [24]. Rainfall and infiltration change the soil characteristics greatly [25]. Some physical qualities of the soil change during rainfall, such as the water content, matrix suction, pore water press, and total stress [26; 27]. The volumetric water content is the ratio of the volume of water to the unit volume of soil and it increases during rainfall. Matrix suction is a sensitive parameter when unsaturated soils encounter rainfall and it is differently affected for soils with varying levels of rainfall infiltration [28; 29]. The pore water press increases during rainfall and reduces the soil's shear strength. Slopes with greater inclination have larger pore water press [30]. Total stress is the basis of stability analyses that are used for calculating the factor of safety [31]. However, all of the above studies measured one or several of the physical quantities of the soil and lacked a comprehensive reflection of the changes in soil properties during landslides. The landslide is a typical example of gravity-based erosion. The sediment yield of landslides varies with the presence of a number of factors [32; 33]. The time scale of the impact of a landslide on the sediment yield in the basin is large. To comprehensively analyze sediment transport, it is necessary to investigate the landslide history of the basin for at least the preceding 100 years [34]. The landslide sediment yield of soil that is affected by an earthquake under rainfall has been studied and quantified [35]. One model that is used to express the contribution of shallow landslides to sediment yield as a rainfall characteristic function has been established [36]. Another model called SHEETRAN was established in order to analyze the impact of rainfall on landslides and sediment transport. It was applied to the Valsassina Basin, which is a wide glaciated valley with a U-shaped profile. The superficial deposits that are found on the valley's slopes consist of calcareous-dolomitic chaotic material with loose and sharp-edged fragments. [37; 38; 39]. The effects of rainfall on sediment yield are obvious and the sediment yield increases with an increase in the gravel percentage [40; 41].