Study On Strength Of Soil-root Composite And Its Mechanism For Slope Protection Of Vegetation In Frigid And Arid-semiarid Environment

The Study on strength of Soil-root composite and its Mechanism for Slope Protection of Vegetation in Frigid and Arid-semiarid Environment play an important role in the selection of genus and species for slope protection and the best plant combination, restoring and protecting the damaged environment, controlling soil and water loss of slope and enhancing slope stability. The single root mechanical characteristics of two-year-age herbs and shrubs, the reinforced function of shrub soil-root composite, the correlativity between the single root mechanical characteristics of two-year-old shrubs and its anatomical structures, the type of soil-root composite and the mechanism of slope protection were studied, which took Xining basin as an example. The main achievements are as follows:The single root tensile and shear tests showed: both the tensile resistance and the shear resistance of herbs and shrubs roots increased with increasing diameter, and the increment rate is Achnatherum splendens﹥Agropyron trachycaulum﹥Leymus secalinus﹥Elymus dahuricus for two-year-age herbs and Atriplex canescens﹥Caragana korshinskii﹥Zygophyllum xanthoxylon﹥Nitraria tangutorum﹥Lycium chinense for two-year-age shrubs; the single root tensile strength and shear strength decrease with increasing diameter, either power or exponential relations were fitted between root tensile strength or shear strength and root diameter; the tensile strength of herbs single root is about two or three times by shrubs roots; the results revealed that different genus and species have different tensile stress-strain curves. Four herbs roots reflected the elastic characteristics, its average elongation rate of single roots was 40%; five shrubs roots reflected the elastic-plastic characteristics, its average elongation rate of single roots was 15%, and the elongation rate of roots decreased with increasing diameter. According to the root mechanical characteristics and root morphological features, Atriplex canescens, Caragana korshinskii and Achnatherum splendens have some functions for slope protection in the transitional region of Qinghai-Tibet plateau and loess plateau, the degree of slope is 40°, soil is silt.By observing roots anatomical structures of five shrubs, the results showed: the main factors affect tensile and shear strength of single root included the percentage of phloem fibers, wood fibers, the degree and speed of periderm lignifications; the shrubs single root elongation rate increased with increasing area percentage of secondary phloem, the area percentage of xylem is on the contrary; the area percentage of secondary phloem of Caragana korshinskii has reached 45%, showed great single root elongation rate; the area percentage of xylem Atriplex canescens has reached 50%, reflected the better mechanical characteristics.Through the shear tests and triaxial compression tests on five shrubs soil-root composite indicated: the shear strength of shrubs soil-root composite are fitted Mohr-Coulomb rule, its angle of internal friction are nearly equal with soil, however its cohesion is increased 29.4～394.6%; the increment of shear strength and cohesion is Atriplex canescens﹥Caragana korshinskii﹥Zygophyllum xanthoxylon﹥Nitraria tangutorum﹥Lycium chinense; the stain of soil-root composite is smaller than soil at the same stress; the five shrubs soil-root composite can constrain the horizontal destroy, so that enhance the slope stability; soil-root composite can be classified as shallow soil-root composite, deep soil-root composite and mixed soil-root composite; its mechanism for slope protection include the reinforced function of clump roots and the tensile reinforcement of single root; the slope stability of the studied area was estimated by the indexes of shear strength and the method of theoretical calculation, the degree of slope stability of the slopes that have Atriplex canescens and Caragana korshinskii roots are higher than the slopes that have Zygophyllum xanthoxylon, Nitraria tangutorum and Lycium chinense roots.