Study On Tensile And Shear Characteristics Of Roots Of Common Shrubs On Slope

Under the background of ecological civilization construction and poverty alleviation,Guizhou province "county to the high-speed" and under the poverty alleviation "group through" measures,from the source to solve the key point of poverty,that is,to "get rich,first road".However,the construction and development of a large number of exposed slope,is bound to affect the ecological environment.The tensile and shear properties of plant roots are important factors to determine the protection of slope.The tensile properties of plant roots are not only the decisive factors to affect the shear properties of root soil complex,but also the direct indicators to evaluate the protection of plant roots to slope.The shear properties determine the resistance of the root system to shear failure and further affect the fixation characteristics of the root soil.In this study,the effects of root diameter,tree species,root chemical composition,root section microscopic characteristics and root moisture content on the tensile properties of single root were investigated by measuring the pull characteristics and shear properties of single root.The direct shear test was used to study the friction characteristics of the root-soil interface and the shear characteristics of the root-soil complex,and to study the shear characteristics of the root-soil complex under normal pressure,soil moisture content and root diameter.The main findings are as follows:(1)The tensile properties of the roots of the two shrubs varied with the increase of root diameter,which showed positive correlation between ultimate tensile strength and root diameter,and negative correlation between ultimate tensile strength and ultimate elongation.In terms of ultimate tensile strength and tensile strength,Indigofera amblyantha is better than Senna bicapsularis,while ultimate elongation is the opposite.(2)The response of the roots of the two kinds of shrubs to water was different,and the tensile resistance of the roots of Indigofera amblyantha showed a decreasing trend,while the tensile resistance of the roots of Senna bicapsularis improved after absorbing water.In addition,the change of water content did not change the change trend of root diameter and tensile properties.(3)The chemical composition of the two shrubs was different,The Indigofera amblyantha of cellulose content in the three element content is higher.However,the lignin content of Senna bicapsularis was higher.This may be one of the reasons why the roots of the two shrubs respond differently to water.(4)The difference of microscopic characteristics of root section(vessel size,vessel distribution and tissue ratio)is one of the internal factors leading to root tensile resistance characteristics.Among them,with the increase of root diameter,the diameter of conduit of two species of shrub increased gradually.Secondly,the arrangement of root cross section conduit varies with the change of root diameter,and there are differences among different tree species.In addition,the cross section vessel’s area ratio of Indigofera amblyantha root decreased first and then increased with the increase of root diameter,and the cross section vessel’s area ratio of Senna bicapsularis of root decreased with the increase of root diameter.With the increase of root diameter,the porosity of root system decreased gradually,and the relationship between the two was a power function.The higher the porosity of root,the larger the mechanical properties of root.(5)There were differences in the microscopic characteristics of root bark between the two species of shrub.The roots of Indigofera amblyantha was grated and shallower in depth,and the Senna bicapsularis.was gully and deeper in depth.The microscopic morphology of root bark showed that the root skin friction characteristics of double pod cassia was larger.The results of the root-soil interface friction test are consistent with this,that is,when the conditions are consistent,the strength of root-soil complex of Senna bicapsularis.is greater than that of Indigofera amblyantha.(6)The shear strength of root-soil complex increased first and then decreased with the increase of root diameter.When the root diameter of Indigofera amblyantha was 3mm,the shear strength of root-soil complex was the highest,while that of Senna bicapsularis.was the highest when the root diameter was 2mm.Secondly,the shear strength of the root soil complex was positively correlated with the normal pressure.With the increase of soil moisture content,the shear strength of root-soil complex increased first and then decreased.Both have the relative maximum shear strength at the moisture content of 14.3%.