Study On Friction And Anchorage Of Alfalfa Root And Soil Composite In Loess Area

Surface erosion,slope instability and soil erosion caused by soil erosion have become the main problems of China’s ecological environment.Plant measures are the most common,economical and environmentally friendly measures to prevent soil erosion,and are the most effective and basic methods for soil and water conservation.The research and implementation of soil and water conservation measures have reduced the occurrence of soil erosion disasters to a certain extent.In order to study the mechanical properties of the roots of alfalfa in the loess area and the frictional anchoring effect of the root-soil composite during the soil-resistance process,the root system of alfalfa was tested by single root in-situ pull-out tests and root-soil composite shear tests.The technical route combined the experimental measurements and theoretical analysis.The variation of the root coefficient and root cross-sectional area of different diameter segments with the buried depth of the soil was analyzed by root length investigation test.The effects of diameter,root length,root surfacearea,soil water content and other factors on the maximum pullout force of roots were studied by single in-situ pull-out tests.Root-soil composites under the conditions of different shear depth,root area ratio and soil water content were studied by root-soil composite shear tests.The mechanical effects of friction and anchorage of alfalfa root-soil composites were discussed.The research results are of great significance for the study of the relationship between soil and soil and the stability of slopes.The main research results were as follows:(1)Root characteristics of alfalfa.The root diameter,number and root cross-sectional area decreased with the increase of root depth.The diameter,the number and the cross-sectional area of roots decreased with root depth.The root diameter decreased with the length of the root system.and the root length decreases.A power function relationship existed between root diameter and root length.(2)Factors affecting the maximum pull-out force of the root system.The maximum pull-out force of roots increased with the increase of root diameter,and a power function relationship was observed between them.The average maximum pull-out force was related with root length of the root system in a exponential function.The longer the root length,the larger the average maximum pull force.The maximum root pull-out force increased with the increase of surface area of roots in a power function.Under the conditions of five different soil water contents(7.84%,9.66%,13.02%,19.35% and 27.06%),the maximum pull-out force of alfalfa roots increased with soil water content.When the water content increased from 7.84% to 27.06%,the maximum pull-out force decreased by 47.48%.(3)The modes of root failure varied with water content and root diameter.Under the above five water content conditions,with the increase of water content,the root pull-out rate increased,and the fracture rate decreased.The root system had two failure modes: pullout and fracture.When water content was 9.66%,root fracture rate was about 48.28%,and the pull-out rate was about 51.72%.The critical value of soil water content for root fracture and pullout was about 9%.The maximum pull-out force of roots increased with the diameter of root system.If the diameter was smaller than the critical value of root diameter 0.66 mm,the force of fracture was greater than the force of pullout;if the diameter was greater than the critical diameter 0.66 mm,the force of fracture was less than the force of pullout.(4)The root system can enhance the ultimate shear resistance of the soil,and the reinforcing effect of the root system on the ultimate shear resistance of the soil decreased with the increase of soil water content.When the water content was 18.97%,the ultimate shear strength of the root-soil composite sample was 10.02 kPa,and the shear displacement was 70.55 mm.Compared with the bare ground samples,the maximum increment of the ultimate shear strength was 89.41%,and the shear displacement increased about 25 mm.At the shear depth 30 cm,when the soil water content reached about 30%,thereinforcing effect of the root system was very limited,mainly because the root system had a small amount of distribution at this depth and the excess moisture decreased the cohesive force between the soil particles.The reinforcing effect of the root system on the shear performance of the soil decreased with the increase of the shear depth of the soil,and the root system had a more significant effect on the shear strength of the shallow soil.(5)Under the condition of the same shear depth and soil water content,the shear strength of the root-soil composite samples increased with the increase of root area ratio RAR.The higher the RAR,the greater the shear strength of the root-soil composite samples.