Study On Physical And Mechanical Properties Of Herbaceous Root Composite Soil And Stability Of Shallow Loess Slope

Based on the loess erosion landslide in Dongzhiyuan District,Gansu Province,this paper studies the mechanical properties of the root system of herbaceous plants and the strength and permeability of the root composite soil,as well as the slope protection effect of the herbaceous plants.The purpose of this article is to discuss the effect of plants on the slope soil,and then to obtain the feasibility and value of herbal slope protection.First,the basic physical and mechanical properties of the rootless soil and the root content of the root composite soil were obtained through laboratory physical and mechanical property tests,and two herb plants of different growth ages,alfalfa and mugwort,were obtained by field measurement The distribution of root system.Secondly,through the indoor tensile test,the effect of plant growth age and root diameter on root tensile strength was obtained,and a mathematical model of alfalfa main root tensile strength related to root diameter and herb growth age was established.Through indoor direct shear test and variable water head penetration test,the influence rules of plant growth age,root content,root diameter and other factors on the strength characteristics and permeability properties of soil samples with root system were obtained.Finally,based on the laboratory physical and mechanical test results,based on the seepage theory of saturated-unsaturated soil and the analysis theory of unsaturated soil slope,the soil slope calculation model was established with the help of Geo-Studio software,and two plants under different rainfall intensity conditions were obtained.Effects of growth age,root content and slope gradient on transient seepage field and stability of shallow loess slopes.The test results show that the strength characteristics of the root composite soil also follow the Coulomb strength criterion.The root system of herbaceous plants has strong tensile strength,and the impact on the soil is mainly manifested in the strengthening effect of the root system on its cohesion,thereby enhancing the shear strength of the soil and improving the mechanical properties of the soil.Secondly,the effects of the growth age,root content and root diameter of the herbaceous plant on the shear strength of the soil are shown as the value of the influencing factor increases,the shear strength increases first and then decreases,indicating that there is an optimal herb The growth age,root content and root diameter makeits shear strength reach its maximum.The effect of water content is that the higher the water content,the lower the shear strength of the composite soil.The numerical calculation results show that: the root system of herbaceous plants can enhance the stability of shallow loess slopes and improve their stability safety factor,but the impact is limited.Secondly,the growth age and root content of herbaceous plants have different influences on the seepage field and stability of shallow soil slopes under rainfall:(1)The depth of rainfall infiltration on the slope with roots on the surface is significantly greater than that without Slopes with roots,and the higher the root content,the deeper the rainfall infiltration depth,the larger the shallow saturated area.(2)The higher the root content of alfalfa plants,the greater the impact on the slope safety factor,while the change of the root content of Artemisia argyi plant has less impact on the slope safety factor.(3)The effect of plant growth age on the safety factor of shallow root-containing slopes is not a positive correlation,but there is an optimal growth age that makes the slope safety factor peak.(4)With the continuous rainfall and the increase of slope slope,the stability and safety coefficient Fs of the slope shows a trend of gradually decreasing on the whole.In addition,the smaller the rainfall intensity,the more obvious the effect of plant roots on slope stability.