# Stability Reinforcement of Slopes Using Vegetation Considering the Existence of Soft Rock
## 1 Introduction  
Slope stability is one of the very traditional but significant issues related to geotechnical engineering, embankment engineering, dam engineering and landfill engineering [1, 2, 3, 4, 5, 6]. Due to the catastrophic consequence caused by slope failure, many reinforcement methods have been developed, such as drainage systems [7], stabilizing piles [8], reinforcement of vegetation, among others. Due to its environmentally friendly characteristics compared to soil nails, geosynthetics, retaining structures, gabions and shotcrete, the reinforcement of vegetation, such as grass and shrubs, on the slope stability, has been gradually recognized [9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20], and there are an increasing number of slope protection engineering with vegetation grew on the slope in recent years [19, 20, 21, 22, 23, 24, 25, 26, 27, 28]. In fact, vegetation-soil interaction and plant-soil-atmosphere interaction are rather complex, thus the mechanism and effectiveness of vegetation reinforcement on slope stability are significant and it has attracted much attention of researchers. In the past two decades, investigations on the effects of vegetation on slope stability have been widely conducted [12, 29, 30, 31, 32, 33, 34]. Among these studies, some of the studies focus on how the soil properties changed due to the existence of vegetation roots. For instance, additional cohesion due to vegetation reinforcement was investigated and determined through direct shear tests [35, 36, 37]; and both additional cohesion and increased friction angle caused by root reinforcement were determined by using triaxial tests [38, 39]. It has been reported that the vegetation also affected the tension strength of partially saturatedsoils [40]. [PERSON], et al. [41] have reviewed the methods for evaluating the root reinforcement for slope stability using both limit equilibrium method numerical methods, and [PERSON], et al. [42] reviewed the contribution of shrub and tree roots on slope stability under both dry and wet conditions in Hong Kong. Moreover, several studies have been carried out to understand how vegetation can improve slope stability. For instance, [PERSON], et al. [43] modified the root tensile resistance of different species growing on slopes to roots cellulose content. [PERSON], et al. [44] analyzed the effect of vegetation on slope stability based on the results of numerical simulation and concluded that slope angle shows the great effect of variations of the factor of safety (FS). However, the numerical analysis in this study was conducted based on a simplified and hypothetical slope. [PERSON], et al. [45] investigated spatial variance in the distributions of roots and mechanical characteristics of Artemisia sacrorum for root reinforcement on the Loess Plateau of China. [PERSON], et al. [46] critically reviewed the slope stabilization potential of herbaceous vegetation as compared to woody vegetation and summarized the status of slope stabilization with herbaceous vegetation. [PERSON], et al. [47] investigated the slope stability along a road by incorporating the effect of five types of plant roots through numerical modeling technique, and it was found that the factor of safety increased from 22-34% when the slope was reinforced with plant roots. Even though the previous studies have demonstrated the effectiveness and mechanism of vegetation on increasing the stability of the slope, the investigation on the design and geotechnical application of vegetation reinforcement on actual engineering slope (e.g., red-bed slope) are still not enough [44], and most of the studies were conducted based on simplified or idealized soil slope. In addition, the effectiveness of the vegetation reinforcement on slope stability under rainfall conditions is still not clear. This paper aims at the effectiveness of vegetation reinforcement of the actual slope under both dry and rainfall conditions.