## 3 Results
### Deformation  
Deformation is the most important external manifestation of slope failure, and the type and characteristics of slope deformation over time are the most effective means for early landslide warnings [42; 43; 47; 48]. For the slope without any mitigation measures (Figure 5), after 6 min of rainfall, the water began to flow on the slope surface, and then the surface began to be eroded. In the first 60 min of continuous rainfall, the erosion at the toe of the slope gradually intensified. Erosion at various points at the toe of the slope gradually connected, and the toe of the slope kept retreating. The longest retreat distance was 28 cm, and small cracks appeared at the toe of the slope (Figure 5a). During 60-90 min of continuous rainfall, the toe of the slope continued to erode, and large blocks of the slope began to collapse. Erosion gullies longer than 10 cm were formed on the slope surface, and continuous deformation at the toe of the slope formed an upright lateral free face at the front edge of the slope. Tension cracks appeared at different heights on the upper and middle part of the slope as well (Figure 5b). During 90-140 min of rainfall, erosion at the toe of the slope continued, and cracks deepened and widened at the middle part of the slope, gradually connecting and penetrating each other. Large blocks of the slope collapsed along the cracks, and the longest retreat length of the slope surface reached 52 cm (Figure 5c). After 193 min of rainfall, the entire slope failed and slid down with a slide depth of 10 cm and a slide distance of 52 cm (Figure 5d). For the slope with a declining gradient mitigation (Figure 6), water began to flow on the slope surface after 5 min of rainfall, and local erosion was observed at the toe of the slope after 10 min. After 30 min of rainfall, erosion gullies at various points at the toe of the slope had connected and penetrated each other, and the toe edge of the slope kept retreating to a longest distance of 15 cm (Figure 6a). After 60 min of rainfall, the erosion continued at the toe of the slope, and the longest retreat distance was 28 cm. Tension cracks occurred in the lower part of the slope surface as well (Figure 6b). During 90-120 min of rainfall, tension cracks in the lower part of the slope surface deepened and widened, gradually connecting and penetrating each other. Local collapse occurred along the cracks at the toe of the slope (Figure 6c). After 150 min of rainfall, tension cracks appeared at all parts of the slope, and the cracks deepened and widened, eventually penetrating each other and forming multiple transverse cracks that penetrated the slope surface. After 180 min of rainfall, a shallow landslide with a depth of 5 cm occurred along the transverse cracks on the slope surface (Figure 6d), but the entire slope was still stable. Figure 5: The process of failure for the slope without any mitigation measures (**(a–d)** are the 60 min, 90 min, 140 min and 193 min after experimental). Figure 6: The process of failure for the slope with step-by-step mitigation (**(a–d)** are the 30 min, 60 min, 90 min and 180 min after experimental). For the slope with a stepwise drainage channel mitigation (Figure 7), after 5 min of rainfall, water began to flow on the surface, and localized erosion was observed at the toe of the slope after 10 min. After 30 min of rainfall, settlement cracks gradually appeared and deepened near the toe of the slope, and after 40 min of rainfall, the failed locally, and some soil masses collapsed, producing a steep and high lateral free face at the toe of the slope (Figure 7a). After 60 min of rainfall, the toe of the slope was almost completely destroyed after multiple local failures, and the drainage channel at the toe of the slope was left hanging (Figure 7b). During rainfall of 90-120 min, multiple local failures occurred gradually upward along the transverse drainage channels on the slope, resulting in serious damage to the slope surface (Figure 7c).