Study On The Effects Of Root System Of Typical Vegetation On Slope Stability In Shallow Landslide Prone Areas Of Bailong River Basin

The degradation of the ecological environment caused by shallow landslides severely restricts regional development.Longnan,Gansu Province,is located in the shallow landslide-prone area of the Bailong River Basin.In order to compare the slope stability of different vegetation types in the study area,the roots and soil of typical herbaceous(Cynodon dactylon,Artemisia sacrrorum,Digitaria sanguinalis,Clematis florida)and shrubs(Punica.Sepium,Lespedeza.Bicolor,Ziziphus.Jujube and Periploca.Granatum)were selected as the research objects to study the effects of root system on soil physical and chemical properties,and slope stability.The specific study analyzed the distribution characteristics of soil moisture and porosity in the rhizosphere,the difference in carbon,nitrogen and phosphorus content,the preferential flow characteristics and the spatial distribution characteristics of the root system,the shear strength of the slope soil under different water content and root density.Finally,FLAC3 D was used to calculate the factor of safety of the slopes under different modes.The following conclusions are obtained:(1)Compared with the shrub root system,the herbaceous has a significant increase in SOC and soil pore structure.The content of large aggregates in the rhizosphere soil of herbaceous plants is between: 37.88%—72.04%,the largest is Clematis florida.The content of large aggregates in the rhizosphere soilshrub is between: 37.88%—69.30%,the largest is Lespedeza.Bicolor.The soil porosity of herbaceous rhizosphere soil is between: 43.75%—55.21%,Artemisia sacrrorum is the largest.The soil porosity of shrubs rhizosphere soil is from 42.56% to 55.19%,with the largest of Lespedeza.Bicolor.The SOC of herbaceous rhizosphere soil is from 1.25 to 6.81 g/kg,the largest is Clematis florida.The root area ration(RAR)of Punica.Sepium is significantly larger than that of other shrubs(p<0.05).(2)The peak tension of the root system of the shrub is greater than that of the herbaceous.The tensile strength of herbaceous roots is greater than that of shrubs.The root diameter and tensile strength of these plants are both in a significant powerreducing function relationship.The tensile strength of the herbaceous root system is from 5.8 to 115 MPa,with the largest Artemisia sacrrorum.The tensile strength of the root system of shrub is from 4.31 to 89.9 MPa,the largest is Lespedeza.Bicolor.The tensile strength of all plant roots is the best within the range of 0—1 mm root diameter.(3)The slope stability is best at 10% moisture content.Within the range of water content change,the increase of water content decreases the shear strength of remolded soil.Compared with bare land,Cynodon dactylon and Periploca.Granatum roots have more obvious effects on soil shear strength.The rhizosphere soil cohesion of Artemisia sacrrorum increased the most compared with bare land,and the cohesion increment values were 83.30%—195.94%.Compared with the bare land,the increase of the friction angle of Artemisia sacrrorum and Periploca.Granatum to the soil is the most significant.At 10% and 20% soil moisture content,the factor of safety each slope is greater than 1.The Cynodon dactylon has the largest factor of safety(1.23)among herbaceous plants and the Punica.Sepium has the largest factor of safety(1.39)among shrubs.For areas with large changes in water content,Lespedeza.Bicolor has a better ability to resist changes in soil moisture,and still has a certain ability to stabilize the slope when the saturated water content is reached.(4)Based on the slope safety factor under different restoration models of shrubs and herbaceous,the root system of shrubs has a better effect on slope stability.With the increase of root density,some plants will reduce the shear strength of remolded soil.Under the three root density gradients,the shear strength of Cynodon dactylon,Punica.Sepium and Lespedeza.Bicolor remodeled soil decreases with the increase of root density.The root-soil complex of Artemisia sacrrorum and Clematis florida are best at 2 times the root density.The root-soil complexes of Digitaria sanguinalis,Periploca.Granatum and Ziziphus.Jujube had the highest shear strength at 1.5 times the root density.The shear strength of the herbaceous root-soil complex: Artemisia sacrrorum>Clematis florida>Digitaria sanguinalis>Cynodon dactylon,shrubs: Ziziphus.Jujube>Periploca.Granatum>Punica.Sepium>Lespedeza.Bicolor.