## 1 Introduction  
Natural disasters such as landslides and debris flows caused by slope instability are among the most frequent and harmful to human activities considering all kinds of geological disasters [1]. Rainfall is an important factor influencing slope instability [2], and slope ecological protection is a common form of slope protection [3, 4], which is widely used in various projects such as highways, railroads and water conservancy [5, 6]; however, the relationship between rainfall infiltration and ecological slope instability is still poorly understood. Therefore, it is important to study the rainfall infiltration and runoff rules of ecological slopes and determine the quantitative analysis model for ecological slope design. Slope instability landslides are influenced by many factors [7, 8, 9], such as rainfall intensity [10], rainfall duration [11], vegetation type [12], topography and initial slope conditions [13], and the purpose of parametric research is to understand the rainfall infiltration law of ecological slopes and to grasp the magnitude of the role played by various influencing factors [14]. In the 1970s, Japan began using small-scale physical models of slopes for experimental rainfall studies [15, 16]. Laboratory experiments on landslide in a scaled physical model began in the 1980s in Canada [17]. Small-scale slope model tests were conducted in Japan and Canada with increased acceleration in geotechnical centrifuges [18, 19]. However, in the case of centrifuge limitation, the scale effect of the small landslide physical model is significant [20]. [PERSON] et al. [21] analyzed the characteristics and patterns of rainfall infiltration runoff, erosion and sedimentation on slopes under different vegetation types and their interrelationships through field simulated rainfall experiments. [PERSON] et al. [22] conducted infiltration tests with a double-loop infiltrator to investigate the spatial variability of infiltration and found that steady-state infiltration rates generally increased with slope, independent of crop type, and that soil infiltration data were consistent with four commonly used water infiltration models. [PERSON] et al. [23] established an infiltration runoff model for mountain slopes and conducted field flow production and natural precipitation catchment tests; the experimental results were compared with the model to find that the model can better simulate runoff and infiltration, and the measured and simulated values were in good agreement. [PERSON] et al. [24] proposed a joint approach using a dual infiltration model and a kinematic wave model, performed laboratory tests and found that the presence of macropores greatly facilitated the movement of rainwater on the slope surface. [PERSON] et al. [25] conducted model experiments to find how the groundwater table, which generates pore water pressure, is affected by infiltration time lag, surface runoff and lateral flow. [PERSON] et al. [26] constructed a small slope model for artificial rainfall tests and showed that rainfall infiltration leads to an increase in the volumetric water content of the slope and the dissipation of the suction of the initial partially saturated material, resulting in a decrease in effective stress and shear strength, which in turn leads to the occurrence of slope movement and damage. [PERSON] et al. [27] conducted a rainfall landslide test using loose sandy soils and measured and analyzed the dynamic processes associated with landslide movement and groundwater pressure fluctuations during the damage process. The study showed that the increase in water pressure on the upper slope was due to the collapse of the loose soil structure during translational sliding, while the increase in water pressure on the lower and horizontal portions of the slope was due to compression and shearing of the soil by the sliding body. [PERSON] et al.