## 3 Results and Analysis  
### Law of Slope Runoff  
#### 3.1.1 Law of Influence of Cement Content on Slope Runoff  
Figure 7 shows that the slope runoff volume increases rapidly within 30 min after the production of flow, increases slowly within 30-100 min and tends to be stable after 100 min. The main reason for this change in runoff volume in the rainfall process is that, within a short period of time after the start of rainfall, the infiltration capacity of the soil is greater than the rainfall intensity and all the rainfall infiltrates into the soil, with no runoff produced on the surface. With rainfall, the water content of the surface soil increases, and the infiltration capacity of the soil rapidly decreases to less than the rainfall intensity due to the effect of raindrop striking and the filling of soil pores by fine particles, and the slope surface starts to produce runoff. The intensity of runoff increases rapidly. When the rainfall lasts for 30-100 min, the infiltration rate of soil tends to stabilize due to the changes in soil water content and soil surface pore condition, and the change in runoff volume tends to moderate. Combined with Table 4, it can be seen that when the thickness of the  
Figure 5: Artificially simulated rainfall test map. **(a)** Top view; **(b)** Flat view.  
Figure 6: Runoff collection devices.  
substrate is 3 cm, the presence of cement greatly affects the slope runoff generation time, runoff rate, average runoff rate and cumulative runoff rate. When the substrate is equipped with cement, the cement content increases by 1%, the runoff generation time decreases by 0.45 min, the steady state runoff rate increases by 51 mL\(\cdot\)min\({}^{-1}\), the average runoff rate increases by 42.5 mL\(\cdot\)min\({}^{-1}\) and the cumulative runoff rate increases by 10.18 L.  
The time of slope runoff generation mainly depends on two factors: one is the average soil infiltration rate \(i_{a}\leq\) rainfall intensity p on the slope surface; and the other is the amount of water potential energy accumulated on the soil surface. In the early stage of rainfall, due to the role of plant retention, the actual effect of rainfall intensity on the slope surface \(p<\) average soil infiltration rate \(i_{a1}\). With the continuous effect of rainfall, the surface substrate gradually becomes wet, and as the surface substrate moisture content increases, the infiltration rate \(i_{a}\) rapidly decreases until the infiltration rate \(i_{a2}\leq\) in rainfall intensity \(p\). At this time, the slope surface produces water and the water potential energy and the slope reaches a certain critical value. When a critical value is reached between the potential energy of ponding water and the slope, runoff is generated on the slope. In this test, the slope ratio of all experimental slopes is 1:1.75, and the rainfall intensity is 60 mm/h. Therefore, the time required for slope runoff generation actually depends on the size of the infiltration rate \(i_{a1}\). Obviously, as the cement content increases, the infiltration coefficient of the substrate decreases, the time required for the infiltration rate of the substrate from \(i_{a1}\) to \(i_{a2}\) decreases, and the time required for slope runoff generation is shorter.