Study On The Influence Of Root Morphology Of Slope Protection Shrub On Root Mechanical Characteristics

With the development of social economy,ecological slope protection has become the mainstream way of slope treatment.The main principle of plant slope protection is to adjust the hydrological process of slope by using plant stems and leaves,and the root system stabilizes the slope by reinforcing,anchoring,pulling and netting.Root morphology determines the way of soil fixation by root system,and the mechanical properties of root system are the basis of determining the ability of root system in soil fixation.Therefore,it is of great significance to study the root morphology of plants and its relationship with root mechanical properties for slope protection and management.In this study,the mechanical properties of different root forms of Cassia bicapsulafis and Indigofera amblyantha were studied,and the mechanical properties of different root forms were discussed by single tensile test and pull out test.The tensile characteristics and micro-morphological characteristics of the roots of two shrubs were compared by single tensile test of straight roots combined with microstructure observation.The main research results are as follows:(1)The root diameter of straight roots of Cassia bicapsulafis and Indigofera amblyantha has significant influence on the tensile properties of roots.The tensile force of single root is positively correlated with root diameter by exponential function.And the maximum tensile force of single root is 385.23 N and 415.61 N,respectively.The tensile strength of single root is negatively correlated with root diameter.There is no obvious correlation between ultimate elongation and root diameter.The stress-strain curves of Cassia bicapsulafis are multimodal and unimodal,and the stress-strain curves of Indigofera amblyantha are unimodal.(2)The relationship between root diameter and tensile properties of curved root is similar to that of straight root.There is a significant positive correlation between root diameter and maximum tensile force of curved roots of Cassia bicapsulafis and Indigofera amblyantha,and the maximum tensile force increases with the increase of root diameter in a power function relationship;Tensile strength is negatively correlated with root diameter,and the maximum tensile force of the bending root is 270.99 N and 369.29 N respectively.There is no significant correlation between ultimate elongation and root diameter.And the average maximum tensile force of each diameter class of curved root is smaller than that of straight root.(3)The tensile process of bending root is different from that of straight root.The stressstrain curve of bending root shows a "concave" single peak curve.The stress starts at an initial value at the initial stage of the test and increases slowly with strain.The slope of the curve gradually increases with the increase of strain.Finally,the stress increases to the maximum at a faster rate,and the root system breaks.The force-displacement curve of the bending root indicates that the bending root is slow to resist tension.(4)The root bending degree of the two shrubs has no significant influence on the maximum tensile force,but has significant influence on the initial stress displacement and ultimate elongation.There is a significant positive correlation between the bending degree of the bending root and the initial stress displacement of Cassia bicapsulafis and Indigofera amblyantha,The greater the root bending degree,the greater the ultimate elongation.In addition,the initial stress displacement is less than the root length of the bending part,and the limit extension of some root systems is less than the root length of the bending part,that is,some bending roots are broken under bending.Bending root has weak tensile capacity,but the initial stress displacement and ultimate elongation of root system are large,so it has stronger buffering capacity for landslide.(5)The pull-out modes of Cassia bicapsulafis and Indigofera amblyantha bifurcation roots can be divided into three types: complete pull-out failure mode,main root pull-out failure mode and lateral root pull-out failure mode.The F-S curves of root system being pulled out under different failure modes are different.(6)The root diameter of the main root has a significant influence on the frictional anchorage performance between the bifurcation root and the soil.Under the same bifurcation angle,the maximum pullout force is positively correlated with root diameter.The peak slip of Cassia bicapsulafis decreased with the increase of root diameter,but there was no significant correlation between them,and there was no correlation between root diameter and peak slip of Indigofera amblyantha.The initial load increased with the increase of root diameter of Cassia bicapsulafis and Indigofera amblyantha,but the correlation between them was not significant.(7)Bifurcation angle has a significant influence on the frictional anchorage performance between bifurcation root and soil.When the root diameter is similar,the larger the bifurcation angle is,the greater the maximum pull-out force is.Peak slip and initial load have no obvious correlation with bifurcation angle,and they have no obvious change with the increase of bifurcation angle.Bifurcation angle has no significant effect on peak slip and initial load.There is no significant difference in root-soil friction anchorage performance between two kinds of slope protection shrubs.(8)There are significant differences in root cross-sectional micro-morphology between Cassia bicapsulafis and Indigofera amblyantha.The pore size of Cassia bicapsulafis is uniform and the root bark is thin,accounting for a small cross-sectional area;There are great differences in the pore size of Indigofera amblyantha,with thick root bark and a large proportion of cross-sectional area.The micro-morphology of tensile section of two shrubs is also different,the root section of Cassia bicapsulafis is uneven,and the tear of fiber bundle is obvious The fiber filaments of Indigofera amblyantha root bark are obviously torn,but the xylem fracture is smooth.