# Shear Strength Analysis and Slope Stability Study of Straight Root Herbaceous Root Soil Composite
###### Abstract  
The instability of bare slopes is a prevalent concern. The root system of herbaceous vegetation enhances the shear strength of shallow slope soil. This study investigated the mechanism of the root-soil system as well as the effects of different influencing factors on the shear strength of the soil and slope stability. In particular, indoor experiments were conducted on rootless undisturbed soil (RUS) and undisturbed soil with a root system (USRS) using a triaxial compression apparatus to analyze the slope stability of composite soil with a _Tagetes__ercta_ root system. Significance tests and correlation analysis of the factors affecting shear performance were conducted. The slope reinforcement effect by the plant root system was simulated under 24 working conditions using the MIDAS finite element method. The results revealed the influence of the root content, moisture content, and stress on the shear strength of USRS, as well as the contribution degree and influence of these variables on the slope stability. Both RUS and USRS exhibited strain hardening during shearing. A strong negative (positive) correlation was observed between the internal friction angle (\(\varphi\)) (cohesion (c)) of the USRS and the root content (moisture content). The maximum deviatoric stress during shear failure of the USRS was 1.29 times higher than that of the RUS. Moreover, the root content was positively correlated with the slope safety coefficient and the slope of the line under different working conditions, whereas the slope angle was negatively correlated with the slope safety coefficient. The reinforcement effect by the root system resulted in a 11.2% increase in the safety coefficient and the improved stability of slopes with an angle larger than 1.5%. The findings of this study provide new insights into shallow slope stability in practical slope protection projects. T +
Footnote †: journal:  
0000-0001-3390-3390][PERSON]  
0000-0001-3390-3390][PERSON]  
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desiccation-induced vegetation. Planting vegetation is the preferred approach to reconcile water resource conflicts, address ecological concerns, and prevent soil erosion [8]. Vegetation plays a significant role compared with other engineering methods due to benefits such as improving the eco-environment, reducing water loss and soil erosion, conserving water sources, and consolidating slopes. It is an effective measure for economic and environmentally friendly prevention and control. Employing vegetation to improve the stability of slopes is the future direction for slope protection [9; 10]. In recent years, research on the mechanism of vegetation-based slope protection has yielded fruitful results, both domestically and internationally. Scholars have conducted numerous studies on the mechanical properties and mechanisms of root-soil fixation using both indoor and outdoor experiments as well as numerical simulations. These experiments mainly involve direct shear, in situ shear, triaxial compression, and unconfined compressive strength tests. Prior research confirms that root-soil interactions can enhance soil shear strength [11; 12]. Therefore, an in-depth exploration of herbaceous plant root-soil interactions in mountainous zones is warranted to establish a scientific foundation for enhancing slope stability and preventing soil erosion [13; 14; 15]. Herbaceous vegetation ecology protection technology presents an economically and environmentally viable method for soil reinforcement and aligns with sustainability principles. This approach supports soil consolidation and mitigates shallow landslides. Table 1 summarizes the quantitative evaluation methods for various plant roots' effects on soil reinforcement proposed by existing literature [16; 17; 18; 19; 20]. Several studies on slope stability [21; 22; 23] have employed Mohr-Coulomb strength theory to show that the extra cohesion provided by plant root systems gauges soil reinforcement effectiveness. [PERSON] et al. investigated the impacts of the plant root system on