The stability of vegetation slope is closely related to the shear strength of the root-soil composite, which is mainly affected by the action of roots and the action of water. In this study, the effects of root content and water content on the shear strength and its indexes were analyzed by direct shear test and soil-water characteristic curve test, and a strength calculation model of the root-soil composite was derived. The results show that the roots of Robinia pseudoacacia can significantly enhance the shear strength of the soil. The cohesion first increases and then tends to be flat with the increase of root content, and the internal friction angle increases with the increase of root content, but the growth rate is small. The shear strength decreases rapidly with the increase of water content. The changing trend of cohesion and internal friction angle is consistent with the shear strength, but the change range of the internal friction angle is small. The influence of root content and water content on the shear strength of soil is mainly reflected in the change of cohesion. The root-soil composite is regarded as unsaturated soil containing roots, and the strength calculation model of the root-soil composite is derived. The calculated value of the strength model is close to the measured value of test. The research has a certain reference value for the strength calculation of the root-soil composite.

The accuracy of the results is influenced by capacitive components. This paper focuses on loess in the Yichuan region and establishes the relationship between unsaturated loess matrix suction and complex resistivity parameters based on complex resistivity tests and soil-water characteristic determinations. It reveals the variation patterns of their spectral characteristics and derives formulas for loess saturation degree and complex resistivity. The research results indicate that the excitation frequency is negatively correlated with the amplitude and phase of complex resistivity. When the frequency is less than 1000 Hz, the amplitude and phase of loess complex resistivity fluctuate significantly, stabilizing gradually after it exceeds 1000 Hz. With the increase of matrix suction, the amplitude, real part resistivity, and imaginary part resistivity of loess gradually increase, with their correlation influenced by the applied frequency. Loess capacitance and dielectric constant decrease with the increasing matrix suction. A loess saturation degree-complex resistivity model is established using the real part resistivity and imaginary part resistivity, and the model can be used for monitoring moisture changes in loess. The research results provide new methods and perspectives for utilizing the frequency dispersion characteristics of loess in geological disaster monitoring.

Loess has porous metastable structure and water sensitivity, and is prone to collapse when it encounters water. The disintegration of loess is one of the main factors that promote soil erosion, collapse, landslide and other geological disasters in the Loess Plateau. As a low cost and convenient material, cement improved loess (CIL) is widely used in loess foundation and slope engineering, but there are few researches on its anti-disintegration. The disintegration behavior of loess before and after the improvement was analyzed through the laboratory disintegration test and scanning electron microsope (SEM) test under the condition of CIL and different content, and the improvement effect and mechanism of cement on loess disintegration were explored. The results show that cement can greatly improve the anti-disintegration ability of loess. At low content, CIL still has a complete disintegration process, but cement can fill the intergranular pores and hinder water transport. Meanwhile, cement hydration and its interaction with loess particles can enhance intergranular cementation, thus delaying the disintegration process of loess. With the increase of cement content, the anti-disintegration effect is more obvious, and the cumulative disintegration component is almost 0. The minimum cement content of soil sample without disintegration is 3%. The results are of great significance to the study of erosion resistance of loess and the design of disaster prevention engineering.