A Roots Distribution-based Study On The Stability Of Ecological Slope

As an engineering technology, root reinforcement to slope has been widely applied in theslope protection, but the theoretical study on it has lagged behind practical applications. on thebasis of current literatures and the systematical study on the destroy principle of root-soilfriction bond, root morphological models, root-soil interaction and mechanical models, thisdissertation applies the fractal theory, Geotechnical engineering slope theory and Plant ecologytheory comprehensively and takes the interaction between soil and complex root group intoconsideration to provide theory basis and approaches to the application of quantitative rootresearch into the numerical analysis on slope stability. Meanwhile the dissertation offers atheory for the new artificial structures or reinforcement methods stimulating the root effects onslope reinforcement. The dissertation combines field investigation and lab experiments,experimental research and numerical stimulation to focus on the study of the distribution ofbermuda grass and nerium indicum root forms. On the basis of morphological characteristics ofthe roots, a fractal software Fractal1.0was developed to calculate fractal dimension for differentroots. The dissertation uncovers the root-soil interactions by analyzing the effects of tilted,horizontal, vertical, intersected and complex root-soil composites on the soil strength, as well asthe effects of the roots of both plants on the stress-strain of the soil. Besides, in the light of thefractal dimension between root models in numerical stimulation and actual measurements, therelevance between root fractal dimension and slope soil displacement field is studied and aquantitative calculation method on the slope stability reinforced by soil-root interaction is putforward in the dissertation.Main Innovations1. The root configurations of bermuda grass and nerium indicum are described; rootdistribution characteristics are determined from root length, surface area, volume, dry weightand length density, which are the most related morphological index to slope reinforcement; thereinforcement abilities of both plants are analyzed in terms of root configuration andmorphology; a fractal software Fractal1.0is developed specializing in the fractal dimension fordifferent roots.2. Tensile strengths of the roots of bermuda grass and nerium indicum are experimentedand a conclusion is drawn that the tensile strength of root decreases with the increase in rootdiameter; the related fitting formula on root diameter and tensile strength is also worked out.3. the effects of tilted, horizontal, vertical, intersected and complex root-soil compositeson the soil strength are studied for the first time with the help of triaxial test system; the stress-strain and shear strength parameter of both pure soil and rooted soil are obtained; theresults are concluded that the different root-soil composites can be sorted in descending orderby their soil-reinforcement abilities as following: complex root-soil composite, intersectedroot-soil composite, vertical root-soil composite, horizontal root-soil composite, tilted root-soilcomposite.4. The effects of stress field and displacement field of different roots characteristics onthe slope soil are studied by using numerical analysis in an innovative way. The relevancebetween root fractal dimension and slope displacement field is presented on the basis of therelevance between root models in numerical stimulation and actual measurements, which leadsto a conclusion that different plants has different effect on the stress field and displacement fieldon slope, but both can reduce displacement and enhance stability. As to the slope rooted withbermuda grass, the surface displacement is decreasing with the growth of the length, amountand distribution density of fibrous roots, while as to the slope with nerium indicum, the surfacedisplacement is decreasing with the growth of the amount and distribution density of lateralroots, most stable when the angle between tap and lateral root is45。～60。.5. As is shown through fractal dimension and the fitting formula on slope displacement,with bermuda grass rooted in at10plants per meter, the horizontal displacement of slopesurface soil reduces by41.2%, vertical displacement by20.4%and total displacement by20.9%respectively compared with the soil without plants in. With nerium indicum rooted in at5plantsper meter, the horizontal displacement of slope surface soil reduces by25.7%, verticaldisplacement by7.7%and total displacement by7.6%respectively compared with the soilwithout plants in.6. The reinforcements of both plants on the slope soil are restricted to the shallow layers.Therefore both roots serve to improve the cohesion and decrease lateral displacement ofshallow soil and play a role of reinforcement for soil surface.7. The root-soil interaction can be stimulated by finite element analysis to show theeffects of root on the surface stress field and displacement field of slope. Finite element methodcan be applied in practice to quantitatively analyze the stress-strain of slope soil and it alsoprovides guidance in selecting appropriate plant and distribution density.8. The relevance between and the slope surface displacement is determined. With thefractal dimension increasing, the root abundance and the amount of root branches are growingwhile the surface displacement reducing. Therefore the fractal dimension of roots can reflect theroot effects on the slope soil.