Study On The Mechanism Of The Tree Grass Mixture Slope With Root Reinforcement

In recent years, research on plant slope has attracted much attention of scholars at home and abroad, especially as a new slope protection technology which combined with engineering technology and ecological technology has been paid more and more attention. According to the indoor and outdoor experimental studies on stems and leaves of plants and the reseach on root-soil complex by many predecessors, it has showed that plants have play a significant role in preventing soil erosion and improving the stability of soil slope.This thesis regards vetiver and lobular privet as wel as their root-soil complex as the research objects, and the research on mechanism of mixed roots reinforcing slope was carried out. All the research works are funded by the the following fund projects, these fund projects are include the National Natural Science Fund Project "Study on Molding Mechanism of High-Strength Forest-Grass Mixed Roots and Reinforcing Mechanism of Root-Soil Composite in Plants Slope" (No:31270671), The State Forestry Administration of the "948" project "Technology Import on High Stability of Ecological Slope Protection for Integration of Forest and Grass" (No:2012-4-76), and Hunan Provincial Natural Science Foundation Fund Project "Study on Mechanical Characteristics of Plants Slop" (No:12JJ5015)etc.A series of experiments on root-soil composite which contained with vetiver and Ligustrum quihoui were finished, such as rainfall simulation tests, water loss rate tests, soil erosion resistance tests, direct shear tests, tri-axial shear tests and so on. Under the influence of different factors, some problems such as water content of slope soil, soil erosion resistance, strength of root-soil composite, and its stress-strain relationship etc. were studied. At the same time, the effect laws of some factors on slope deformation and stability have also been explored, these factors are include mixed roots content, density of roots, roots distribution, and water content changing etc. Through the research the main innovative conclusions are as follows.The hydrological effect1. Because of plant roots are existed, the moisture content of soil can be retained within a certain range. So that the water content of soil is balanced, and the stability of the slope is improved. But the height of the slope and the planting density of mixed plants are the influence factors of this balance effect.2. In the case of planting mixed with forest and grass, for a slower slope, the bigger of planting density is, the larger of effective root number is.3. It is obvious that the ablity of soil in resistance to disintegration is enhanced by the plant roots. The higher of root content in soil is, the stronger of its ablity in resistance to disintegration is. The smaller of soil moisture content is, the longer of time which needed to completely disintegration is, and so that the ablity of soil in resistance to disintegration is more enhanced.4. Using the software of Origin to fit the experimental data, it was found that with the increase of roots content, the ablity of soil in resistance to disintegration is increased, and the relationship of them follows a power function. Moreover, in the conditions of different initial water content and different effective root density, A formula which is used to calculate the time required for soil complete disintegration is proposed.The mechanics effect1. The study found that the shear strength of the root-soil complex is still according with Mohr-coulomb’s theory. Furthermore, Along with the decrease of water content, the shear strength of root-soil composite gradually increased, at the optimum moisture content it reaches the peak value.2. It has found that the existence of the plant roots can effectively increase the shear strength of root-soil composite. But for herbaceous plants, this enhancement effect is mainly reflected in the increasing of cohesive force of root-soil composite. In a certain range, for the shear strength of root-soil composite, the higher the root content is, the greater the contribution of roots is.3. For the shear strength of root-soil composite, the influence rule of taproot and oblique root have the Similar effects, the shear strengths are all increased with the increasing of root biomass.4. In this study, we have discussed the effects of different distribution mode of load on the calculation results in Fibre Bundle model. By improving the existed model, an analysis model which can more closed to the actual situation is put forward. On the other side, it has been proved that if take the parameter v as 0, The calculated results is accord with the actual situation still further.5. The study show that when the plant roots are existed in slope soil, which have the function to coordinate the deformation of soil.On the basis of existed researches, some experimental and theoretical studies on root-soil composite of mixed with roots of forest and grass in ecological slope engineering were carried out. For this ecological slope which was mixed planted with Vetiver and Ligustrum quihoui, the effect of plants on hydrological and mechanics of slope were explored in this thesis. These research results have laid a theoretical foundation for further promotion of ecological slope protection technology research and its application.