# Experimental Study on the Permeability of Ecological Slopes under Rainfall Infiltration Conditions
## 3 Test Results and Analysis
### Variation Law of Volumetric Water Content
Therefore, the monitoring points in the lower part of the slope respond the fastest. Based on this reason, the response time of the water content monitoring point in the middle part of the slope is the second, and the response time in the upper part of the slope is the smallest. At the same time, due to the formation of a transient saturation zone in the lower part of the slope, the rainwater in this area would continuously flow to the monitoring point w-x-2 under the action of gravity, so the water content of the monitoring point w-x-2 increases faster than that of the monitoring point w-s-1. The relationship between the volumetric water content of the surface monitoring points of the four types of overburden slopes and time is shown in Figure 5.  
Figure 5: Relationship between volumetric water content of slope surface monitoring points and time: (**a**) water content of soils on the slope surface of four overburden slopes versus time; (**b**) water content of soil in the middle of slope surface of four overburden slopes versus time; (**c**) water content of the soil in the lower part of the slope surface of four overburden slopes versus time. According to the data curves of the water content monitoring points at a vertical distance of 20 cm from the slope surface and 40 cm from the slope surface, it can be seen that during the period of 4 h rainfall and 7 h natural evaporation, the water content variation curve generally shows a trend of first unchanged, then increased, then unchanged, then decreased, and finally unchanged. At the beginning of the rainfall, the rainwater has not yet infiltrated the location of the water content monitoring points, so the values of each water content monitoring point inside the four slopes remain unchanged, and the values of the water content monitoring points are the water content of the initial state of the slope soil at this time. As the rainfall continues, the rainwater continues to infiltrate, and the values of each monitoring point begin to increase at different times, indicating that the rainwater has infiltrated the location of the water content monitoring point. After several hours of rainwater infiltration, the slope soil at each water content monitoring point reaches a saturated state, i.e., the peak plateau of the curve, so that the slope soil has experienced the process from an unsaturated state to a saturated state. During the natural evaporation stage after the cessation of rainfall, the rainwater in the slope soil migrates downwards under the action of gravity, and the slope soil would be over from the saturated state to the unsaturated state. Then, the slope soil would finally be in a moist state with a certain water content, which shows the trend of the curve gradually decreasing and finally leveling off in Figure 5. It is worth noting that the faster the infiltration rate of rainwater in each slope, the shorter the time period from the initial constant value to the beginning of the increase in the curve, and the larger the value of the peak plateau reaches afterward. Comparing Figure 5c with Figure 5a,b, it can be seen that the infiltration rate of rainwater (i.e., the slope of each curve rising in Figure 5) in the lower part of the four types of overburden slopes is larger than that in the upper part of the slopes and the middle part of the slopes, resulting in a shorter response time (i.e., the horizontal coordinate corresponding to the dividing point of the water content monitoring points from unchanged to increasing) for the initial increase in water content compared to the upper and middle parts of the slopes. When the location of the slope surface and slope type are certain, the response time of water content monitoring points closer to the slope surface is shorter.