Study On Mechanism Of Soil Reinforcement By Roots And Slope Protection Technology

With the rapid development of China economy, mining, road construction,water conservancy and other infrastructure generated a lot of artificial slope, including the cutting slope and embankment filling slope, a large number of exposed slope not only can cause soil erosion, but also triggered landslides and debris flows and other geological disasters, but also destroyed the original vegetation, damaged the environment.The effect on environment increases with the increasing scale of construction, it is no longer the local issue of a given area or a certain range, but the overall problem affecting achievement of the overall objective of ecological environment.Vegetation maintaining slope stability can effectively overcome the shortcoming of engineering measure maintaining slope stability.When vegetation maintaining slope stability exert the function of soil reinforcement and slope protection of vegetation,at the same time,it can fully exert landscape and environment effects of vegetation, exert the functions of restoring the ecologic, protecting environment and landscaping. Use of vegetation measures or use a combination of vegetation and engineering approach to reinforcement slope, reach the goal of strengthening the slope, but also to restore the ecologic and beautify the environment. As environmental awareness gradually increasing,ecological restoration and environmental protection can not be avoided during the project development and construction, the project development and environmental protection must all take into account in order to promote economic sustainable development. Therefore, the slope protection aims not only to protect the slope, stable slope and reduce soil erosion, but also taking into account the need to restore the vegetation and abundant landscape. In recent years, use of vegetation in slope protection is pay the increasing attention, slope protection by vegetation has become a new trend. Based on Soil Mechanics, Composite material mechanics, Soil& Water Conservation, Forest Ecology and Mathematics theories, In-situ test combining laboratory test and trial method combining theoretical analysis,the paper conducted in-depth study of the plant roots stabilization mechanism and slope protection technology.Paper first detailed the mechanism of plant roots solid soil, the action of roots solid soil include:roots reinforcement mechanism, where the soil reinforced with root,the root regarded as three-dimensional prestressed reinforcement materials, the shear strength parameters C andφ of the root soil complex increased; root anchoring mechanism,when the perpendicular deep coarse roots across the shallow loose weathered layer anchored to the deep stable layer,roots play the role of pre-stressed anchor on the slope; root decompression mechanism, root absorbing water and plants transpiration can effectively reduce the soil moisture content, reduce the soil's pore water pressure, increase soil shear strength parameters C andφ;the root biological characteristics such as uneven surface, a large number of root-knot and root hairs, surface secretions and root shape are conducive to increasing the cohesive force and the friction between root and soil,conducive to increasing the soil C value andφvalue, thereby enhancing the shear strength of the root-soil complexes.The paper proposed a new theory on mechanism of plant root protection slope from the perspective of composite materials. The soil with plant roots was regarded as a special composite material, a large number of interweaving roots like the random distributing fibers, the soil with roots like a fiber-reinforced brittle composite material.root can restrain crack and increase the strength and ductility of soil. By analyzing the action of root resistance cracking and increasing soil strength and ductility the author descripted the mechanism of plant root protection slope. As root higher tensile strength and ductility compare to soil, and the significant differences of deformation modulus, exist dislocation trend between the root and soil during the co-deformation by the external force.The cohesive force and the friction between root and soil can restrain this dislocation, then root pulled, so when the soil into the plastic state the shear stress was gradually transferred to the root system and diffused. Thereby the shear strength and ductility of the root soil complex can be increased,and ultimately improve the stability of the slope. Root resistance cracking and enhancement were as follows:in the micro-crack propagation stage, roots increased the shear strength of composite soil mainly by changing the micro-crack propagation path to increase the energy dissipation, and the increasing amplitudes of the shear strengths was relatively small;in the plastic crack propagation stage, roots improved the shear strength of composite soil mainly by diffusion and transfer the shear stress,and the increasing amplitudes of the shear strengths was relatively big. Root resistance crack and increasing soil ductility were as follows:root diffusion and transfer the stress and strain relatively uniform, the emergence of rupture surface was slow down; in addition, roots tensile and barrier effect prevented the coherent of local shear failure, the dropping extent of the shear strengths of composite soil was slow down from the peak intensity to the residual strength,the ductility of soil improved.The bond strength of interface between soil and root is the important factor that affect shear strength and ductility of the root soil composite materials, the action of root resistance cracking and increasing soil strength and ductility depends on the bond strength of interface.This paper analyzes the composition and influencing factors of the bond strength of interface between soil and root, the process of roots pulled out regarded as the root with the surrounding soil medium shear slipping process, and puts forward that the shear strength of interface between soil and root is the coupling of friction and adhesion of interface, and using Mohr-Coulomb criterion describes the shear strength of interface between soil and root, then the final limit anti-pull force formula of roots is derived. Based-on the root's stabilization mechanism of composite material, root can restrain crack and increase strength, the soil with root will consume more energy during shear failure as compared with the soil without root.If the consuming energy when roots pulled from the soil called pull-out power, the consuming energy when roots pulled broken called fracture power, crack propagation must overcome the pull-out power and fracture power of root before the soil damage under the principle of energy conservation and conversion. Using energy principle studied root's resistance cracking and enhancement action, then a calculating formula of shear strength Increment of one point in the composite of root and soil was educed. A theory is established that the shear strength Increment of one point mainly relates to root's area ratio,areal density,the ratio of length and diameter,tensile strength and the cohesion and friction coefficient between the roots and soil.Finally using the self-made direct shear apparatus the indoor direct shear test on the 300mm×300mm×300mm large-size soil samples with roots and without root done, through contrasting the shear strength of the soil samples with root with that without root obtained the shear strength increment value of the soil samples with root Contrasting the incremental value with the calculation results of calculation model on root enhancement, find the two very fit, the calculation model has been verified.The theory on root resistance crack and increasing soil strength and ductility was verified by the indoor and large-size in-situ direct shear test.1,An experiment of different confining pressures on root-soil composite and plain soil under the same conditions of soil water content and density was carried out by using shear test controlling shear rate 0.1mm/min.Four confining pressures of 100,200,300 and 400kPa were tested. Based on the experiment results, a relationship of shear strength and confining pressures between root-siol composite and plain soil as well as shear stress and shear displacement is established. Results show that:(1)the shear strength of root-soil complex in direct proportion to normal pressure, the shear strength of root-soil complex also is also consistent with mohr-coulomb law;(2) When the soil's moisture content and dry density is constant, with the root volume increasing the cohesion C of complex was significantly increased, internal friction angleφonly increased to some extent,but the effect was not obvious;(3)the fracture toughness of the soil with root is larger than the soil without root,root can increase the soil's ability of resistance shear; there is outstanding positive correlation between root volume and fracture toughness;(4) root can increase the slippage and displacement of soil when shear failure,can increase the soil's ductility, root volume ratio is the important factors affecting the soil's ductility, and there is outstanding positive correlation.2,In-situ direct shear tests on the undisturbed soil and four camphor root-soil compo-site systems are conducted at the foot of the Nan-Wang mountain. By comparing the shear streng-th and displacement of the soil without root and four soils with roots,the mechanical effects of the root system on slope protection can be evaluated. The results show that:(1)compared with the shear strength of soil without roots,the increasing amplitudes of the shear strengths of four soils with camphor roots are 35%,55%,64% and 78% respectively, the residual strength of soil also increased, the increasing amplitudes of the residual strengths of four soils with camphor roots are 50%,62.8%,71.6% and 77.8% respectively, the increasing amplitudes of the residual strength is higher; (2) the displacements in the intensity peak point of four soils with roots are 1.36 times,1.52 times,1.56 times and 1.72 times as that of the soil without root respectively, the soils with roots can withstand greater deformation before cut break, the root system increases the ductility of the soil; (3) the displacements at the strain-softening stage of four soils with roots are 1.4 times,1.675 times,1.825 times and 2.05 times as that of the soil without root respectively, the curve at the strain-softening stage of four soils with roots are more moderate compared with that of soil with-out roots,the reducing amplitude of the shear strengths of the soils with roots after the peak point is lower, the soil with roots can remain a high strength when a larger strain arising, so the ductility of the soil with roots increases; (4) The relations between the load and displacement of the root-soil composite systems and the undisturbed soil all show a linear relationship and almost coincide at the beginning stage of the shear process,a rounding curved relationship with the continuous increase of the shear, when approaching failure the curve of soil with roots are more moderate compared with that of soil without roots, so the ductility of the soil with roots increases.The experiment showed that various physical properties come out in the process of macroscopic shear destruction of root-soil complexity were consistent with the function mechanism analysis of soil reinforcement by roots.The formation of ecological protection must have two necessary conditions:①living plants;②combining with civil engineering or non-life plant materials. No living plants, slope protection by vegetation would be impossible to maintain, in order to achieve the vegetation effects, ecological effects and landscape effects of ecological protection as soon as possible, often combining with civil engineering or non-life plant materials.The paper introduces the slope protection technology with vegetation,and take the ecological protection of a soil slope within the first bid of Jingyi highway for example to introduced the application of hydraulic spraying and seeding technology.During engineering design of vegetation maintaining slope stability, landscape effect and function of improving environment should be fully considered after the vegetation engineering is put in Practice. Based on the principles of ecosystem ecology landscape ecology and restoration ecology,when selecting vegetation types of maintaining slope stability,the paper advanced that vegetation can meet with Protection requirement,On the other hand vegetation can be adapted to habitats of afforestation and cultivating grass,namely,can satisfy adaptable tree and grass for right soil, and with native plant-based, supplemented by introduction of alien plants.the slope plant communities configuration should follow:Shrub Grass combination, pioneer plant matched with medium-term plant and objective plants, Configuration density fit and the principles of landscape effects. Only according to the type of slope deformation, geological conditions, topography, soil character, slope angleand climatic conditions, targeted to select the appropriate plant and a reasonable allocation of communities in order to fully exert the action of slope protection, ecological restoration and landscaping.In order to scientifically and rationally evaluate the quality of slope protection by vegetation, and provide reference,theoretical and technical support for the engineering design of slope protection by vegetation, in the paper 13 important evaluation indexes were presented and constituted the quality evaluation system of slope protection by vegetation from the ecological effects, functional effects,landscape effects three aspects. The weight of each index was determined by means of the Analytic Hierarchy Process, using the fuzzy comprehensive evaluation method a fuzzy overall evaluation model of quality of slope protection by vegetation was established, thus a comprehensive quality evaluation system about slope protection by vegetation initially established. The comprehensive evaluation system was used in the comprehensive assessment of project quality of Jingyi expressway slope protection by vegetation, through its score of comprehensive evaluation we can see the overall quality of Jingyi expressway slope protection by vegetation superior. By comparative analysis we found that the evaluation results can basically get a reasonable explanation and be consistent with the actual situation.