Research On Reinforcement Mechanism Of Vegetation Roots For Soil Strength And Its Model Test In Cold And Arid Environments

In this paper, dynamic pull-out tests and indoor direct shear tests are conductedon herbs. The in-situ shear tests, indoor direct shear tests as well as finite elementnumerical simulation method are conducted on soil without roots and shrub root-soilcomposite systems, so the enhancement effects of herb roots and shrub roots for slopeare comparatively analyzed and the stability of slope is evaluated. Through the aboveresearch, the main conclusions are as follows:The roots of herb and shrub in the testing areas are observed and counted. Theresults show that the root system of Elymus nutans and Achnatherum splendens isfibrous system and the roots are rich in quantity. The root systems of Elymus nutansare denser and longer than that of Achnatherum splendens, so the protection range ofthe roots of Elymus nutans for soil is relatively wider than that of Achnatherumsplendens. And the roots of the two herbs can significantly reinforce shallow soil ofslope and reduce soil and water loss. Besides, the main distribution type of Caraganakorshinskii and Zygophyllum xanthoxylon is taproot system, and the lateral roots ofCaragana korshinskii are short and capillary, while that of Zygophyllum xanthoxylonare longer and larger relatively. At the same time, the roots of Caragana korshinskiiand Zygophyllum xanthoxylon grow better on slopes with angle30than thoseplanted on slopes with angle45.Field dynamic pull-out tests on two kinds of herbs show the pull-out resistanceof Caragana korshinskii and Zygophyllum xanthoxylon increase with the growing ofthe roots length, the roots diameter and the number of fibrous roots. And the dynamicprocesses of the pull-out resistance for two kinds of herbs are almost the same, that is,the pull-out resistance gradually increases with the time passing and then when itreaches the peak, it decreases rapidly to zero at last.The indoor direct shear tests on two kinds of herb root-soil composite systemsshow that the herb roots can significantly improve the cohesive and the shear strengthof soil. And the cohesive value of the roots of Elymus nutans for soil is greater thanthat of Achnatherum splendens.Statistical values on the roots of the two kinds of shrub root-soil composite systems with angle30and45at the shear plane in in-situ shear test show that themain roots of Zygophyllum xanthoxylon root-soil composite systems are anchored inthe soil of the slope, and the roots mainly slip during the process of shearing. Some ofits lateral roots fail by tinseling or shearing, the relatively shorter lateral roots arepulled out, and the rest which are longer slip. The roots of Caragana korshinskiiroot-soil composite systems are mainly pulled out or slip. During the process ofin-situ shear tests on soil without roots and shrub root-soil composite systems. Theshear resistance and the shear strength of the Caragana korshinskii root-soilcomposite systems and the Zygophyllum xanthoxylon root-soil composite systems arelarger than that of soil without root, and the relation on the shear strength is the samewith the indoor direct shear test result. Based on the difference of in-situ shear testsand indoor direct shear test for soil without root and shrub root-soil compositesystems, the results of in-situ shear tests is more accurate by comparing the types,pressure and size of the samples.Based on the results of soil without roots and shrub root-soil composite systemsin in-situ shear tests,2D finite element numerical simulation method are conductedon slopes without roots and with shrub roots. The results show that the verticaldisplacements were larger than the horizontal displacements, and the angle of slopehas a great influence on the vertical displacements, horizontal displacements andshear stress. The displacements and the shear stress increase with the growing of theangle of the slope. Besides, the safety factors of slopes without roots as well as slopeswith Zygophyllum xanthoxylon roots or Caragana korshinskii roots are larger thanone(>1), so all of the slopes are stable. And the safety factors of the slope plantedwith Zygophyllum xanthoxylon roots or Caragana korshinskii roots are greater thanthat of slope without roots, which reflect that plant roots can enhance the stability ofslope. The results of simulation are consistent with the in-situ shear test.