Study On The Mechanical Effects Of Plant Roots For Enhancing The Strength Of Slope Soil In Cold And Arid Environments

In the research, the northeast region of Xining basin and its peripheral regionsare adopted as the test areas. The study is made about the mechanical effects of plantroot for three kinds of shrubs Caragana korshinskii, Zygophyllum xanthoxylon,Nitraria tangutorum and two herbaceous Elymus dahuricus, Agropyron trachycaulumfor enhancing the strength of slope soil in cold and arid environment, which are allplanted in self-built test site in Qinghai University in the north of Xining city. Theresearch mainly includes the following aspects: the determination of the contents ofthe main chemical components in shrubs and herbs roots, and the correlation betweenthe changing of the contents of chemical components and the single tensile properties;the determination of the mechanical properties of shrub roots; the test about root andsoil composites shear strength and the effects of the root contents to the shear strengthof root and soil composites. The results are as follows:Based on the determination test of the contents of chemical composites in fiveplants roots, the contents of four kinds of chemical composites hemicelluloses, lignin,cellulose and pectin and their changing rules in plant roots, are measured andanalyzed. Meanwhile the research also investigates into the effects of the changingrules of the contents of four chemical components on the single root tensile properties,which shows: the contents of four main chemical components in two herbs whosegrowth periods are ten months and seventeen months from high to low ishemicelluloses>lignin>cellulose>pectin, and among the four chemical contents, thecorrelation between the cellulose contents and the single root tensile properties isrelatively more obvious than the other three ones, which means: the diameter of plantroots and the cellulose contents is negatively related, and the contents of cellulose andthe tensile strength is significantly positively related.The test is made on three shrubs with different growth periods in the test area,which determines the mechanical properties such as root area ratio (RAR), root lengthdensity (RLD), root density (RD) in different measuring depths from the slopesurface to the max growth depth of plant roots, and which also analyzes the relationship between these three mechanical property indexes and the measuringdepths. The results show: for three shrubs whose growth periods are ten months andseventeen months, their main roots focus on the depth of0~20cm range from theslope surface, and with the slope measuring depth increasing, the root area ratio, rootlength density and root density decrease gradually, the lateral roots maximumextended length is25cm in horizontal direction of the slope, the lateral roots ofZygophyllum xanthoxylon are relatively more and stranger than that of Caraganakorshinskii and Nitraria tangutorum. In addition, when the growth period increasesfrom ten months to seventeen months, the roots increase gradually in slope unit soil,and the root diameter also increases, and the root area ratio, root length density androot density of three kinds of shrubs increase gradually.By the means of the laboratory direct shear test and triaxial compression test ofroot and soil composites which contain three kinds of shrub roots and the soil withoutroots, the index of shear strength of soil without roots and the roots and soilcomposites which contain different roots from one to fifteen is measured andanalyzed. The results show: the shear strength of the soil with roots is significantlygreater than that of the soil without roots, which suggests that plant roots can increasethe strength of root and soil composites significantly, and when the contents of rootschange, the shear strength of root and soil composites change correspondently, andthere exists an optimal root contents; in the range of certain slope measurementdepths, with the root area ratio, the root length density and the root density increasing,the shear strength index cohesion c of root and soil composite also increase gradually,showing the enhancement effects of roots to the composites is relatively stronger.