Shear strength characteristics of slope soil in dumping site in high-cold mining area

The paper aims to study the shear strength characteristics and the influencing factors of the root-soil composite systems of herbs in the dump slope of the high-cold mining area. The dumping site of Jiangcang mining area of Muli Coalfield, located in the northeastern Qinghai-Tibet Plateau, was selected as the study area. For the dump slope which was planted with Elymusnutans Griseb., combined with Poacrymophilakeng, density, moisture content and root content of different depths of root-soil composite systems below the surface of slope were tested; the cohesion and the internal friction angle of soil without roots and root-soil composite systems were obtained by indoor direct shear test. The correlation among density, moisture content and root content and the shear strength indexes(cohesion and internal friction angle) were obtained by the grey correlation method. The test results show that the density and moisture content of root-soil composite systems are smaller than those of soil without roots at the same sampling position and horizon of dump slope, the root content of the second layer(10-20 cm below the surface) of root-soil composite systems is smaller than that of the first layer (0~10 cm below the surface) significantly, and the average reduction amplitude of root content in the second layer is 31.66% compared with the first layer; moreover, the cohesion of root-soil composite systems is larger than that of the soil without roots, the average increment amplitude of cohesion of root-soil composite systems in the first layer and the second layer are 32.69% and 13.42% respectively compared with soil without roots, while the internal friction angle does not show obvious change law; the correlation between strength indexes(cohesion and internal friction angle of root-soil composite systems) and density is higher, the next is moisture content, the last is the root content. The results of this study have certain theoretical research value and practical guiding significance for ecological restoration of the dump slopes in the alpine mining area, which can scientifically and effectively prevent geological disasters such as soil erosion on slope and shallow landslides.