# Experimental Study on the Permeability of Ecological Slopes under Rainfall Infiltration Conditions
## 3 Test Results and Analysis  
### Variation Law of Volumetric Water Content  
Figure 4 shows the relationship between the volumetric water content of each burial depth monitoring point inside the artificial slope without vegetation H1 and time under the rainfall condition. The artificial slope H1 without vegetation has been growing for one year in a natural environment and has experienced many wet and dry cycles during this period. Therefore, the initial water content at different slope locations is not consistent, resulting in different starting points of the water content versus time curves. As shown in Figure 4, all the water contents of measurement points w-s-1, w-s-2, w-z-1, w-z-2, w-x-1, and w-x-2 begin to increase after 3 h of rainfall. Among them, the water contents of measurement points w-s-1, w-z-1, w-z-2, w-x-1, and w-x-2 begin to increase after 1.5 h of rainfall, indicating that the depth of rainfall infiltration at this time is not less than 20 cm in the upper part of the slope, and not less than 40 cm in the middle and lower part of the slope. Within the following 1.5 h, the water content of the measurement point begins to increase, indicating that after 3 h of continuous rainfall, the depth of rainfall infiltration in the upper part of the slope, the middle of the slope, and the lower part of the slope is not less than 40 cm. Within the natural evaporation stage of 7 h after the end of 4 h of rainfall, the water contents of measurement points w-s-3, w-s-4, and w-z-3 have increased, which indicates that the infiltration depth of rainwater in the upper part of the slope is not less than 100 cm, and the infiltration depth in the middle part of the slope is not less than 60 cm. Meanwhile, it is found that the water contents of measurement points w-s-3, w-s-4, and w-z-3 begin to increase only after the end of rainfall, which indicates that there is a lag in the infiltration of rainwater into the slope. However, the water contents of the monitoring points w-s-5 buried at a distance of 150 cm from the upper part of the slope and w-z-4 buried at a distance of 100 cm from the middle part of the slope remain unchanged, indicating that the rainwater infiltration depth does not reach the corresponding burial depth value. In summary, during 4 h of continuous rainfall, the rainfall infiltration depth of the artificial slope without vegetation reaches 40 cm in the upper, middle, and lower parts of the slope, and during 7 h of natural evaporation, the rainfall infiltration depth reaches 100 cm in the upper part of the slope, 60 cm in the middle part of the slope, and 40 cm in the lower part of the slope. This indicates that the infiltration rate of rainwater in the slope is different, showing the rule that the lower part of the slope surface is the largest, the middle part of the slope surface is the second, and the upper part of the slope surface is the smallest. It is worth noting that the infiltration rates of the other three types of slopes with overburden also show similar patterns. Figure 4: Relationship between water content and time of artificial slope without vegetation. The reason for the phenomena shown in Figure 4 is that the initial state of the surface soil of the slope is in a dry state, and the rain falls on the entire surface of the slope after the rainfall begins. As the rainfall continues, part of the rainwater that falls on the upper part of the slope infiltrates into the interior of the slope and moves to the lower part of the slope under the action of gravity. The other part of the rainwater forms runoff on the slope surface and gradually flows towards the lower part of the slope. Finally, the two parts of the rainwater converge at the lower part of the slope to form a temporary saturation zone and then penetrate into the interior of the lower part of the slope along the cracks in the lower part of the slope, resulting in a faster increase in water content in the lower part of the slope compared to the upper and middle parts of the slope.