Experiment Study And Finite Element Analysis Of Mechanics Effect Of Vegetation Slope Protection

The soil fixation and slope protection by vegetation can be mainly reflected in two aspects: hydrological effect by the stems and leaves of plants and the mechanical effect by the root of plants.Hydrological effect includes rainfall interception effect and rainfall reallocation effect by plant stems and leaves,effect of reduction in raindrop splash erosion by foliage,and plant residues and surface runoff retardation effect by plant above-ground residues.The mechanical effect includes reinforcement effect by fibril roots,anchorage effect by taproots.This paper is based on the geological environment of highway ecological slope in Zhangjiakou area.The paper highlights the research mechanical effects of slope protection by the roots of Sabina vulgaris.The experiment and finite element analysis were carried out mainly from the reinforcement effect of cypress root,the mechanical properties of root system,the frictional resistance of soil-root interface and the anchoring effect of cypress root.Concluded as follows:1.Through the triaxial test,it is concluded that the incorporation of root in the soil significantly increases the shear strength of the soil,and the cypress is effective in strengthening the soil.The effect of root reinforcement is mainly to improve the strength of the soil by increasing the cohesion of the soil,but the effect on the internal friction angle is negligible.The cohesion of the root-soil composite increases with the increase of the root density.The cohesive force of root-soil complex decreased with the increase of water content.Through data fitting,the cohesion of root-soil complex was inversely proportional to the logarithm of moisture content.By investigating the relationship between the cohesion increment and the root content of the root complex,the shear strength formula of Reinforcement effect by the roots of Sabina vulgaris was derived on the basis of Coulomb's law.2.Through the tensile test of Sabina vulgaris' s roots,it is found that the tensile strength of the root is positively correlated with the diameter which is approximate to the power function relationship.3.According to the interface direct shear test between Sabina vulgaris's roots and soil,the frictional resistance increases linearly with the deeper of the root penetration into the soil.Under the experimental conditions,between the Sabina vulgaris' s roots and soil interface,the coefficient of friction is 0.589,the cohesion is 13.73 kPa and the interfacial friction angle is 24.399 °.The derivation shows that the constitutive relation of the soil interface with the root of Sabina vulgaris in the direct shear test is hyperbolic.4.Through the simulation of finite element software,it is concluded that geological stratification is an important condition for landslide occurrence.Comparing the slope without Sabina vulgaris,although the depth of Sabina vulgaris' s root does not reach the potential slip surface,however,it still plays the role of anchoring.The slope model is improved both in terms of sliding deformation and stability coefficient,which shows that the Sabina vulgaris has a certain contribution value to the slope stability.Under the condition of heavy rainfall,the sliding deformation of the slope increases sharply and the slope stability coefficient dropped significantly.Compared with the effect of vegetation root reinforcement,the hydraulic effect plays a leading role in the stability of the slope.Comparing the solid slope effect of the two root models,it is concluded that the effect of root perpendicular to the slope is better than the root perpendicular to the ground.Therefore,the selection of slope protection plants should not only consider the depth of vegetation growth,but also consider the divergence of vegetation roots.Sabina vulgaris' s root density,wide angle of growth is more suitable as a slope vegetation choice.