Effect of vegetation roots on soil hydraulic and mechanical characteristics under rainfall

Rainfall infiltration is the main inducing factor for the instability of unsaturated soil slopes, and root water uptake and reinforcement play an important role in preventing shallow landslide. In order to explore the influence of vegetation root on the soil hydraulic and mechanical properties under rainfall, a self-designed soil permeability coefficient measuring device considering the effects of vegetation was used to study the soil water characteristic curve (SWCC) and permeability coefficient of Festuca Arundinacea, Ophiopogon Japonicus, Ligustrum Vicaryi and bare soil under two different rainfall conditions (3.0mm/h and 5.0mm/h) were studied. Then, the direct shear tests of root-soil composite with different water contents and root contents were carried out. Finally, the slope stability under different rainfall and vegetation was simulated by GeoStudio. Results show that: root water uptake can effectively reduce soil water content and increase soil suction, and its influence range is about 2-3 times the length of the root system. Root water uptake can also significantly improve the soil water retention capacity. The air entry value of vegetation soil is larger than that of bare soil, and the permeability coefficient of vegetation soil is about one order of magnitude lower than that of bare soil. Among the three different types of vegetation, the effect of Festuca Arundinacea and Ophiopogon Japonicus on soil water content and suction is more significant than Ligustrum Vicaryi. Root reinforcement mainly increases the soil shear strength by improving the cohesion of the root-soil composite, but has little effect on the internal friction angle. The cohesion of the root-soil composite is affected by soil water content, root content and root distribution, which increases with the increase of root content, and decreases with the increase of water content. When the roots are vertically distributed, the cohesion of the root-soil composite is greater than when the roots are placed horizontally and inclined. Vegetation can effectively improve the stability of the shallow slope under various rainfall conditions, but has little effect on the stability of a deep slope. The safety factor of all three types of vegetated slopes is higher than that of bare soil slopes.