# Experimental Study on the Permeability of Ecological Slopes under Rainfall Infiltration Conditions
## 3 Test Results and Analysis
### Calculation of Unsaturated Permeability Coefficient
#### 3.3.5 Unsaturated Permeability Coefficient
As shown in Figure 9a-c, it can be seen that whether in the upper part, middle part, or lower part of the shallow soil of the four overburden slopes, the permeability coefficients of the shallow soil of the _Cynodon dactylol_ overwhelden slope H2 and the _Cynodon dactylol_ and _Magnolia multiflora_ mixed slope H4 are always small, whereas the permeability coefficients of the shallow soil of the artificial slope H1 without vegetation and the _Magnolia multiflora_ overburden slope H3 are always large, indicating that planting _Cynodon dactylol_ or mixed planting _Magnolia multiflora_ and _Cynodon dactylol_ on the slope can reduce the permeability coefficient of the shallow soil of the slopes to a certain extent. It is worth noting that the permeability coefficients of the _Magnolia multiflora_ overburden slope H3 and the artificial slope H1 without vegetation show different magnitude relationships at different experiment stages, indicating that planting _Magnolia multiflora_ alone on the slope cannot always increase or decrease the unsaturated permeability coefficient of the surface soil of the slope, so further analysis of the data is needed. From Figure 9, it can also be found that with continuous rainfall, the permeability coefficients of the shallow soil of the four overburden slopes show a trend from stable to fluctuating and finally stable. In the early stage of the experiment, the permeability coefficient of the shallow soil of the _Magnolia multiflora_ overburden slope H3 always increases first, but its maximum value is always larger than that of slope H1 without vegetation. Overall, the permeability coefficient of the shallow soil of slope H1 without vegetation is greater than that of the _Magnolia multiflora_ overburden slope H3, indicating that the straight root system vegetation would increase the permeability coefficient of the shallow soil in the early stage of the test, but the influence of the root system vegetation of _Magnolia multiflora_ on increasing the permeability coefficient of the shallow soil is not significant in the later stage of the experiment. The reason for these phenomena is that _Magnolia multiflora_ is a shrub plant with a conical root system and the most developed horizontal root system, and the effective root system is mainly distributed in the soil layer within the range of 0-60 cm [30]. Therefore, the pore structure of the soil layer within a vertical distance of about 60 cm from the slope surface is destroyed, and the gap between the _Magnolia multiflora_ root system and the soil during rainfall would provide a priority channel for rainwater infiltration. Therefore, in the early stage of rainfall, the permeability coefficient of the shallow soil of the _Magnolia multiflora_ overburden slope H3 is larger than that of slope H1 without vegetation. The rainwater falling on slope H1 without vegetation carries away some of the soil on slope H1 without vegetation to form slope runoff, whereas the other part of the rainwater continues to infiltrate. This rainwater infiltration would form the seepage channel of slope H1 without vegetation, which would continue to be expanded as the rainfall continues into the later stage. In contrast, the reinforcement effect of the _Magnolia multiflora_ root system makes the seepage channel of the _Magnolia multiflora_ overburden slope H3 not easy to expand. Therefore, the permeability coefficient of the shallow soil of slope H1 without vegetation in the later stage of the test is larger than that of the _Magnolia multiflora_ overburden slope H3.