EFFECT OF SOIL MOISTURE CONTENT ON SHEAR STRENGTH OF ROOTED SOIL IN LOESS REGIONS OF XINING BASIN

This paper aims to deeply investigate the role of vegetation roots in faxing soil and increasing soil strength and probe into the influence of soil moisture content on soil strength. It selects Changlinggou catchment in Xining Basin as the tested site. Four types of local vegetation were chosen as the tested species. They are Caragana korshinskii Kom., Nitraria sphaerocarpa Maxim., Achnatherum splendens(Trin.)Nevski, and Agropyron trachycaulum Linn. Gaertn. Five sets of undisturbed and remolded rooted soil with soil moisture contents increasing from 6% to 22% were prepared for indoor direct shear tests. The results show that all of the vegetation roots possess a capacity of significantly resisting deformation of rooted soil, but as moisture contents increase, the root role in resisting soil deformation is reduced. At the same moisture content, the cohesion of rooted soil is generally larger than that of non-rooted soil. The growth rate of cohesion is 1.94~12.17 kPa and the growth amplitude is 34.50% ~360.69% in comparison to the non-rooted soil. However, the same trend did not occur in the internal friction angle. A binomial function can describe the relation of soil moisture content with its cohesion for all of the soil. Moreover, as the moisture content increases from 6% to 22%, the cohesion declines from 28.50% to 61.78% and the internal friction angle declines by 38.73%. The works possess theoretical and practical significance on further exploring the factors influencing the shear strength of herb and shrub root-soil composite systems, adopting dominant local plants to carry out slope protection, and effectively preventing and controlling regional soil erosion, shallow landslide and other geological disasters.