Experimental Study On Shear Strength Of Root-Soil Composite

With the continuous development of China’s infrastructure construction, the new technology which combined with engineering technology and the ecological technology to meet the environmental requirements is more and more extensive realized in the process of construction. Plants slope protection technology as one of the new technology, its economic and environmental advantages are increasingly apparent in engineering construction. The study on root-soil composite of domestic and foreign is still ascendant, and many encouraging results have been obtained. But most of past research is still in qualitative analysis phase. On the study of interaction of root and soil, foreign scholars put forward many theories hypothesis, and many domestic scholars also draw lessons from their experience. But its calculation theory is still far from to meet practical needs. Therefore, further study on the interaction between root and soil, and establishing reasonable shear strength calculation model for root-soil composite is the premise of solving the problems of plants slope stability analysis. On the basis of existed research results at home and abroad, this thesis make the root-soil composite as the research object, to carry out the relevant research. All research in this thesis are funded by the National Natural Science Foundation-funded project "Research on Molding Mechanism of High-Strength Forest-Grass-Mixed Roots and Reinforcing Mechanism of Root-Soil Composite in Plants Slope"(No:31270671), the State Bureau of Forestry948project "Technology Import of High Stability of Ecological Slope Protection for Integration of Forest and Grass"(No:2012-4-76) and Hunan Provincial Natural Science Foundation "Study on Mechanical Characteristics of Plants Slop"(No:12JJ5015). Through a series of experiments on vetiver’ root-soil composite, the characteristics of shear strength of composite in the different conditions are studied in this thesis. The main contents of the research work and its achievements are as follows:(1) The research on roots distribution of vetiveria zizanioides:Through the analysis of roots of vetiveria zizanioides which grown in test chamber for three years, and three indexes are selected to describe the roots distribution pattern. The first is the relationship between the total cross-sectional area and depth of roots, the depth of the cross-sectional area is halfway point of each layer. The second is the relationship between the quantity and depth of roots. The third is distribution of root diameters along depth. According to these three indicators, we can comprehensively to describe the distribution law of vetiver roots number and its cross-sectional area in different depth. On this basis, the characteristics of shear strength of root-soil complex in different depth is studied, and the ecological slope stability research is carried out(2) The experimental study on tensile strength of plant roots:Based on a series of indoor tests for the roots of vetiver, the tensile strength characteristics which are related with the diameter and length of root have been researched. The tested results showed that, with the increase of diameter and length of root, its tensile strength decreased gradually, and the effects of root diameter is more obvious. At the same time, the calculation model of tensile strength of root is improved, and especially for vetiver, the model parameters are given. The calculated results are in good agreement with those of the tested results, it is proved that the theoretical model is reliable, which provides a theoretical foundation for the research of shear strength of root-soil composite, so that this is also an essential prerequisite for stability alysis of plants slope.(3) The experimental study on shear strength of root-soil complexThrough direct shear test on root-soil complex of different plant density, and based on the existed shear strength calculation method of root-soil complex, two kinds of feasible calculation models are established, and a series of conclusions are obtained as follows:①It is significantly that the shear strength of root-soil composite has been enhanced when the vetiver’ roots are existed. But the increase of cohesive force is obvious, and the increase of internal friction angle is relatively small, when the roots are existed in the composite.②The change of cohesive force is related to shear strength of without root soil. In the same situation (root number and root diameter), the higher the soil shear strength is, the greater the increased cohesive force of the composite.③The lower the moisture content is, the greater the increased strength of root-soil complex.④With the increase of roots number, the growth of cohesive force and internal friction angle is not according to the linear change. At the same time when the cross-sectional area of root is more than a certain ratio, and increasing amplitude of the cohesive force value is decreased.⑤For different diameter of roots, different calculation models must be adopted, so that it can make the calculated results more agree with the actual situation. It should be pointed out that the herbaceous and woody plant roots have different contributions on the shear strength of root-soil complex.