| The fragile ecological environment of the Loess Plateau,represented by the Ansai District of Yan’an City in northern Shaanxi Province,has led to an increasingly sharp contradiction between the growing production needs of human beings and the fragile ecological environment,and a large number of exposed slopes have caused increasingly serious soil erosion and geological disaster problems.In recent years,with the application of plant slope protection technology and the promotion of ecological engineering,the contribution of plant roots to the stability of slopes has attracted more and more attention.Compared with engineering measures such as slurry hanging net,anchor cable and anti-slip pile,plant slope protection technology has the characteristics of ecological and environmental protection,landscape beautification,sustainable use and low maintenance cost.Therefore,the study of root consolidation mechanism can provide theoretical guidance for the application of plant measures in slope greening,slope stabilization and ecological restoration.In this paper,a field vegetation survey was conducted in Ansai District,Yan’an City,Shaanxi Province,to find the pioneer plants suitable for soil consolidation and slope protection in the loess area of northern Shaanxi Province,and on the premise of identifying Artemisia spp.as the pioneer plants,in situ field slope pulling tests and indoor straight shear tests were conducted on Artemisia spp.The research results are as follows(1)The group conducted a natural slope vegetation structure survey in the rural areas of the study area since 2014 to date for 323 loess slopes formed in the last three years mainly along country roads,and identified 33 most dominant plant species,mainly cold-tolerant,droughttolerant and barren species,among which the number of herbaceous and woody plant species were equal,but the frequency of herbaceous plants surveyed reached 74%,and the frequency of Artemisia spp.among herbaceous plants The frequency of occurrence of herbaceous plants reached 23%.This confirms that herbaceous plants and Artemisia spp.among them have a clear advantage in the number of plant community structures.The root system of Artemisia spp.was studied and found to be woody,stout,and deeply embedded,while retaining the characteristics of a large number of herbaceous fibrous roots and a large horizontal extension range during the juvenile stage and in the shallow soil.Artemisia has the advantages of community number,root material and root growth characteristics,so it is used as a pioneer tree species for soil consolidation and slope protection in loess areas in northern Shaanxi.(2)In order to adapt to the study of the damage process of root-soil complex under the special environmental conditions in northern Shaanxi,we designed and developed the in-situ pullout test apparatus independently,and investigated the effects of root stem level,root morphology,soil compactness and soil moisture on the tensile properties of Artemisia spp.Different root morphologies can lead to differences in the expression of force-displacement(FS)curves of the root-soil complex during force-deformation damage,as well as differences in the microscopic evolution of the root-soil complex during tensile deformation damage.The soil compactness is one of the leading factors affecting the maximum pullout force,and the degree of influence is different at different stages of root development;the test results that the maximum pullout force of root system increases and then decreases with the increase of soil moisture are due to the different roles played by the mud film formed by the combination of soil particles and moisture in the process of thinning and thickening with the increase of moisture.(3)In order to study the fine-scale strength characteristics of root-soil composite and the mechanical properties of root-soil action during force damage,indoor direct shear tests were conducted on the root-soil composite,and it was found that both plain soil and root-containing soil follow the Moore-Coulomb soil strength formula.Different rooting methods have a greater effect on the shear strength of the soil,and the mixed rooting method has a better effect on the resistance to soil deformation than the single rooting method.(4)In order to study the interaction mechanism between the microscopic root system and soil body in the root-soil composite,the interaction between the root system and soil body on the microscopic scale obtained from numerical simulation was used as the theoretical basis,and the macroscopic deformation and damage process of the root-soil composite obtained from the in situ pulling test and the fine strength characteristics of the root-soil composite obtained from the indoor direct shear test were synthesized and analyzed.It was found that the root system in the deformation damage,the root system in different locations due to the combined influence of its force direction and material properties,resulting in the root system in the shear damage surface of the damage form of different;shear damage surface tangent line and the root system by the direction of tension angle is the key factor to determine the root-soil composite damage form. |
