Shear Strength Analysis and Slope Stability Study of Straight Root Herbaceous Root Soil Composite

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 erecta 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 (phi) (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.