# Stability Reinforcement of Slopes Using Vegetation Considering the Existence of Soft Rock
## 3 Results
### Effect of Vegetation on the Slope Stability with Rainfall
Figure 9: Distribution of suction within the slope on different days during the rainfall for the case without vegetation reinforcement: left with a rainfall intensity of 10 mm/day and right with a rainfall intensity of 50 mm/day. Further, the increase of FS of the slope with different rain flow conditions and soil strength parameters is presented in Figure 12. The horizontal dash in these figures denotes the initial FS without vegetation reinforcement. It is more apparent that the addition of vegetation more or less increased the FS of the slope for different rainfall cases. Reinforcement of slopes using vegetation can be a feasible way to enhance the stability of the slope. However, the FS increase caused by mature forest and the young forest is not always larger than the increase caused by grass and shrubs. The significant findings should be given more attention when using vegetation for the reinforcement of slope in practice. In addition, the increasing proportion for various rainfall conditions also positively or negatively varied with the rainfall time. This also indicated that the increase of FS due to vegetation reinforcement is dependent on the actual situation of the slope. Figure 10: Incremental deviatoric strain during FS calculation and total displacement during rainfall for the case without vegetation reinforcement: left with a rainfall intensity of 10 mm/day and right with a rainfall intensity of 50 mm/day. Figure 13 depicts the comparison of FS for different cases without rainfall and with a rain amount of 100 mm. Obviously, FSs for the cases without rainfall are evidently larger than those for the cases with rainfall, no matter what a heavy rain or a light rain. For the case without vegetation reinforcement, the FS value calculated for the case with larger rainfall intensity (50 mm/day) is smaller than that calculated for the case with smaller rainfall intensity (10 mm/day). This is following the fact that the temporary heavy rain is more dangerous for slope stability. However, for the cases with vegetation reinforcement, FS for the heavier rainfall case is not always larger than that for the smaller rainfall cases, which demonstrated that the addition of vegetation has changed the potential slip mode, compared to that without vegetation. Furthermore, in terms of the four types of vegetation, it seems that the effectiveness of shrubs is not better than that of grass, which may be attributed to that the increase of both cohesion and influencing the depth of shrubs root has changed the potential sliding surface. Similarly, the effectiveness of a mature foresee is not always better than that of a young forest. These phenomena indicate that the reinforcement effect of the four vegetation is not proportional to their cohesion addition and influencing depth. In practice, the design of vegetation reinforcement should be analyzed in advance, and it does not match the expectation that the deeper the reinforcement depth is, the safer the slope is. Figure 11: Factor of safety of the slope with different rainfall conditions and soil strength parameters: (**a**) 10 mm/day rainfall and average soil strength parameters; (**b**) 10 mm/day rainfall and minimum soil strength parameters; (**c**) 50 mm/day rainfall and average soil strength parameters; (**d**) 50 mm/day rainfall and minimum soil strength parameters. Comparison of the FS increase proportion using average and minimum soil strength parameters is further depicted in Figure 14. The more closer the point is to the diagonal dash line, the more closer the proportion of FS increase using average and minimum  
Figure 12: Increase of factor of safety of the slope with different rainfall conditions and soil strength parameters: (**a**) 10 mm/day rainfall and average soil strength parameters; (**b**) 10 mm/day rainfall and minimum soil strength parameters; (**c**) 50 mm/day rainfall and average soil strength parameters; (**d**) 50 mm/day rainfall and minimum soil strength parameters.