| This paper takes Amorpha fruticosa as the research object,which a deciduous shrubs widely distributed in Shendong mining area at the junction of Shaanxi and Inner Mongolia.The strength characteristics,elastoplastic characteristic,constitutiverelation and the elastic deformation characteristic of the straight roots and lateral root branches of the Amorpha fruticosa with diameters from 1-5mm were measured.And the vulnerable parts and load types of Amorpha fruticosa test roots were also identified.This experiment will clarify the mechanical properties of the single root material of purple spike,enrich the research on the mechanical mechanism of plant roots and soil consolidation,and provide a theoretical basis for the selection of plant species in the vegetation of the Shendong mining area and the northern land subsidence area.The results of the research are as follows:(1)Among the ten-year-old Amorpha fruticosa roots,the root surface ratio within the diameter range of 1-5mm reaches 53.61%,which is much larger than that of very fine roots(<1mm)and very thick roots(>5mm).The effect of root soil is the most obvious.The mechanical properties have the greatest impact on the mechanical properties of the root-soil interface.(2)Under axial and radial loads,the ultimate forces of the straight root and lateral root branches of Amorpha fruticose within the diameter range of 1-5mm were positively correlated with root diameters as a power function,the ultimate strength were negative correlated with root diameters as a power function.The angle of the lateral root branch affects the strength characteristics of single root.The greater the angle,the greater the ultimate force and the smaller the ultimate strength.(3)Under axial and radial loads,the straight root and lateral root branches of Amorpha fruticose within the diameter range of 1-5mm all showed elastic-plastic deformation characteristics.Under axial load,the plastic deformation tends to be stable in each cycle,and the proportion of elastic deformation increases gradually.Under radial load,the proportion of elastic deformation tends to be stable,while the plastic deformation gradually increases.Under axial and radial loads,the loading times(19.43 times and 30.88times)of the straight root were slightly greater than that of the lateral root branches(16.79 times and 26.26 times),and the elongation ability of the straight root was slightly better than that of the lateral root branches.However,the elongation rate of the root under radial loads was higher,and it was easier to deform than that under axial loads.(4)The constitutive curve type and curve distribution of the straight root and lateral root branches of Amorpha fruticose within the diameter range of 1-5mm are related to the type of load.Under axial load,the convex σ-ε curve is the main curve type(78.71%,58.06%).Under radial load,the concave curve is the main curve type(54.60%,45.81%),more than 85% of the root fracture mode is sudden fracture.Under the two kinds of loads,the ultimate stress of the root were negatively correlated with the root diameter,while the ultimate strain has no correlation with the root diameter.The ultimate strain of the root under axial load were less than that under radial load,and the ultimate strain of the straight root segment were less than that of the straight root with lateral root branches.The results showed that root of Amorpha fruticosa had little stress change under axial load,and the straight root was not easy to deform.(5)The tensile elastic modulus and the bending elastic modulus of the straight root and lateral root branches of Amorpha fruticose within the diameter range of 1-5mm were negatively correlated with the root diameter as a power function.The tensile stiffness and bending stiffness were positively correlated with the root diameter as a power function.Under axial and radial loads.The percentage of elastic stress and elastic stress in the straight root were greater than lateral root branches,and the elastic strain is smaller than that lateral root branches.The lateral root branches were more easily transformed from elastic deformation to plastic deformation.Under the axial load,the elastic stress and the percentage of the elastic stress of the straight root and lateral root branches were significantly greater than the radial load,and the elastic strain was significantly smaller than the radial load.The elastic deformation properties of Amorpha fruticosa root under the axial load were better.(6)The 1-5mm diameter range of Amorpha fruticosa contains the lateral root branches and the upper and lower root segments.Under axial and radial loads,the order of ultimate force is adjacent upper straight root>lateral root branches> adjacent subordinate straight root.The subordinate straight root with smaller root diameter is the vulnerable part of Amorpha fruticosa root.The ultimate force and ultimate strength of the straight root and lateral root branches had no difference under axial and radial loads,but the ultimate strain and elastic deformation under axial loads were smaller than those under radial loads,and the radial load is the vulnerable load type of the root of Amorpha fruticosa. |
