Research On Mechanism Of Root Reinforcing Soil And Slope Erosion In Slope Protection By Vegetation

As a flexible technique of slope protection, vegetation slope takes both ecological construction and environment protection into consideration, and has been widely used in engineering construction。Vegatation slope has close relationship with science of ecology, environmentology, biology, engineering, landscape and esthetics and so on. As for the reaearch on vegatation slope, in the engineering field, the study usually combines with one or some particular orking points, and then researches the construction technique and engineering prevention measures, however, the mechanism of vegatation slope are rarely carried out deeply; In the ecological field, the study is mainly focus on the biographical mechanical characterastics of the plant on certain working point, and the plant is mainly forest or bush plant but seldom is the herb plant. This paper, based on the scientific program of construction part of department of railway on " the new technique of vegatation slope of railway subgrade slope", and through the test of the relationship of water content and shearing strength, the tensile test of the plant roots of vegatation slope, the pull-out test of the roots and so on, gives a systematic and comprehensive research on the mechanism of vegeking sites, In addition, through investigation on the characteristics of the erosion caused by sloping surfaces, this paper analysizes the erosion mechnism of the slope. The main conclusions and results are as following:1.Under the natural water content, the shear strength of rooted soil has an obvious increase compared to rootless soil in four kinds of plants(tall fescue, bermuda grass, bluegrass, ryegrass).As regard to the scope of increase, the cohesion has a more significant effect compared to the internal friction angle, which shows that the roots enhance the soil shear strength of soil mainly through the enhancement of soil cohesion.2.While keeping the basic content of roots in the soil inviarable, the shear strengh of rootless soil and rooted soil decreases at different level with the increase of water content. Regression analysis of relationship bettween water content and shear strength shows that water content has a logarithmic relationship with cohesion and internal friction angle;3.The diameter of the four kinds of plant roots is all less than 1.0mm, and ninety percent of the roots are distributed in the depth of 0 to 60mm; through regression analysis between content of roots and the depth of the soil layer, the two parameters are in exponential relation, and with the increse of the depth, the content of roots has a decreasing trend.4. When keeping the water content inviarable, the shearing strength increases with the increase of roots content. The roots content has logarithmic ralative relation with the cohesion and internal friction angle, and the roots content has an linear relation with the increased value of cohesion and internal friction angle. The Mohr-Columbia theoretical formula of the root-soil compoud is as follows:τ=(c0+k1Rω-a)+σtan(φ0+k2Rω-b)5.The maximum of tensile force of roots increased as the diameter increases, but the tensile strength reduces, the diameter of roots and the maximum pull-out resistance showed exponential relationship, however, the relationship between the diameter and tensile strength showed power function. The stress-strain relationship of Tall fescue roots and Ryegrass roots exerts Non-linear elastic characteristics, between of which are logarithmic or power relationship, and both are elastic-plastic material; nevertheless, the stress-strain relationship of Bermuda grass roots and Kentucky bluegrass roots accorded to hook's law and exerts linear elastic characteristics, so they are both elastic-plastic material.6.There was not a clearly relationship between pull-out resistance of individual plant roots and the height of plant; however, single roots pull-out resistance and whose diameter has the relationship as exponential function, and which with the root depth presented as a linear duality function relationship. Friction coefficients of four kinds of slope protection of plant roots and soil were as follows:tall fescue 0.29, bermuda grass 0.21, bluegrass 0.35, ryegrass0.37.7. After the vegatation slope, the erosion of slope soil is mainly hydraulic erosion caused by the rainfall。The form of hydraulic erosion is mainly raindrop splashing erosion and slope surface erosion。And the main form of erosion of slope surface is flaky-shaped and rill-shaped。8. Based on the conditions of the research area, under the particular conditions of vertical rainfall and ideal homogeneous slope surface, the critical slope angle of the soil of winward slope isa=45.97°, and the leeward slope is a=39.78°。...