Analysis Of Soil Reinforcement Mechanism And Slope Stability Of Plant Root System

In recent years,plant ecological slope protection technology that takes into account restoration of vegetation and beautification of the environment has become increasingly mature,and has been widely used in highway slope protection projects.The discussion of the mechanism of the soil reinforced by plant roots and the analysis of the stability of plant slope protection are the necessary preparation for the the determination of the highway ecological slope protection construction plan.Based on the principles and methods of soil mechanics,ecology,and fracture mechanics,this research improves the mechanical model of plant root system soil consolidation,and utilizes the test data of the root-soil complex to explore the numerical simulation methods of the plant root system and soil.The developed simulation technology are applied to the stability analysis of the Longlang Expressway slope.The main findings are listed as follows,(1)The relation between the tensile resistance and the root diameter is linear,the relation between the tensile strength and the root diameter is exponential.The fitting results of different plant types are different,while the trend is basically the same.The tensile resistance of the root increased with the increase of root diameter,and the tensile strength decreased with the increase of root diameter.When the root-soil complex is objected to shear failure,the root system will not break completely,and 3 failure mode including rupture,pulling out and slipping may occur.The failure modes of the lateral roots are mostly pulling out and rupture,the failure mode of the main roots focuses on slipping.(2)Based on the fracture toughness and functional principles,the relationship between the shear strength increase of root-soil composites and the fracture toughness of the plant root is established,it can be expressed as △S=kGp.The fracture toughness can be determined by a few parameters including the root diameter,elastic modulus,and root-soil composite cross-sectional area.Through verification,the calculation error of the model constructed based on the Griffith fracture criterion is approximate to 15%,which can meet the requirements of engineering practices.(3)The content of roots in the soil gradually decreases with the increase of depth,the roots of herb plants such as Cynodon dactylon and Lolium perenne are usually distributed in the soil with a thickness of 0-30cm,while the roots of the Magnolia multiflora plant are vertical roots,which can penetrate deep into the soil within 3-5m.Plant roots can effectively increase the shear strength of the soil,and the increasing effect will also be affected by the root content.As the depth of the soil increases,the root content of the complex decreases,and the reinforcement effect of the root system will gradually decrease.The results of the direct shear tests shows that the rootless soil and the root-bearing soil both follow the Mohr-Coulomb strength theory.Plant roots have a greater effect on improving the cohesion of the soil,but have little effect on the angle of internal friction.(4)The embedded model of the rod element in ABAQUS can be used to simulate the interaction between root and soil.The simulation results consistent with the theoretical and test results basically,and show the same trend.The improvement of soil strength is related to the embedding angle of the root.When the embedding angle is equal to 60°,the improvement effect is the best.when the embedding angle is greater than 90°,the enhancement effect of roots is not obvious.Meanwhile,mixed roots is suggested to reinforce the soil in the case of multiple roots.(5)When the total duration of rainfall is fixed,the effect of plant roots on slope safety factor increases with the increase of rainfall.Under the 3 rainfall intensities,the safety factor of herbals to soil is increased by 1.33%,2.08%and 6.1%,respectively.and the safety factor of shrub roots to soil is increased by 3.29%,4.08%and 4.32%,respectively.When the rainfall intensity is constant,as the rainfall duration increases,the safety factor of the protected slope gradually increases first,and finally keeps stable.The stress borne by plant roots is mainly concentrated on the vertical main root,and the magnitude of the stress increases along the root radial direction.The lateral roots distributed around also bear a part of stress.The research results of this paper provide a reliable theoretical basis for analyzing the effect of plant roots on soil consolidation and slope protection,and also lay a technical foundation for the promotion and application of ecological slope protection technology.