Study On The Mechanism Of Soil-root Interaction Of Slope Protection Vegetation And Its Relationship With Slope Stability In Frigid And Arid-semiarid Environment

The vegetation plays an important role in reducing soil water loss, increasing slope stability and improving ecological environment. Soil-root interaction and root strength of vegetation can increase the shear strength of soil, and enhance the stability of slope. In this paper, through mass observation and tests outdoor and indoor, the distribution characteristics of root system, the mechanism of soil-root interaction and its relationship with slope stability were studied, and the main conclusions are as follows:The slope should have better stability and better environment for plants to grow. If the herbs and shrubs of different growth types were blended proportionally, a perfect supplementary function in hydrology effects, mechanical effects, landscape effects will be got.The main distributions of root systems of four herbs are fiber system, about 92% roots were distributed in the depth of 0～30cm underground. The root system of Achnatherum splendens is the strongest among the four herbs. The main distribution type of four shrubs is taproot system, the main lateral roots are rich in its quantity and distribute in the depth of 20～80cm underground.By establishing mechanical models of soil-root interaction, the results are: the herbs root system plays a reinforced function in the soil, the horizontal and vertical root system of shrubs plays a traction function and anchor function respectively. And the mechanical effects of slope protection by herbs and shrubs were correlated with quantity, length and strength of roots.The pull-resistance is measured by in-situ pull-out test for two-year-old herbs and shrubs vegetation, the results indicated that there exists a linear relation between pull-resistance and root quantity of herbs, the pull-resistance increases with the roots quantity increasing, and the pull-resistance of Achnatherum splendens is the biggest among the four herbs, and the pull-resistance of Achnatherum splendens is 27.24N. For shrubs, there exists a linear relation between pull-resistance and root system quantity, a power relation between pull-resistance and root diameter exists, and the pull-resistance increases with root quantity and root diameter increasing.The pull-resistance of Atriplex canescens is the biggest among the four shrubs, and the pull-resistance of Atriplex canescens is 156.67N.This results indicated that the soil-root friction of Achnatherum splendens and Atriplex canescens is the biggest and the effects of two plants for slope protection are the best.The results which are got by using two dimensional finite element method indicated: the slope formed plastic area under the gravity and shrubs roots, and the shearing stress centralized on the slope surface, and the plastic area and centralized area of the shearing stress are the smallest under roots of Atriplex canescens and Caragana korshinskii. The results of evaluation of slope stability showed: the shrubs root system enhance slope safety factor obviously, and the slope safety factor is the biggest under the root system functions of Antiplex canescens and Caragana korshinskii, and the slope safty factor is increased 82% and 50% individually by the soil slope。Considering mechanical effects, hydrology effects, and distribution characteristics of root system, Atriplex canescens, Caragana korshinskii and Achnatherum splendens should be selected for slope protection in the transitional region of Qinghai-Tibet plateau and loess plateau the degree of slope is 40°, soil is silt, and the effect is perfect.