西宁盆地黄土区荷载条件下植被护坡力学效应

为探讨西宁盆地黄土区边坡在荷载条件下植物根系对边坡稳定性的影响,该项研究以西宁盆地西山长岭沟流域为试验区,在自建边坡上种植草本植物垂穗披碱草(Elymus nutans)和灌木植物柠条锦鸡儿(Caragana korshinskii),通过在边坡坡顶施加载荷,边坡坡面布设位移计与土压力盒的方式,监测荷载条件下边坡坡面土体位移与土压力变化;在此基础上,对边坡植被根-土复合体开展剪切试验,分析荷载条件下边坡坡面不同位置处根-土复合体抗剪强度及其变化特征。试验结果表明:在坡顶荷载条件下,在边坡相同位置处的根-土复合体粘聚力c值均大于施加载荷前;3种植物边坡的根-土复合体粘聚力c值均大于相同条件的未种植素土边坡;在荷载条件下,组合植被边坡的坡面土体位移量显著小于单一植被边坡和素土边坡,组合植被边坡在竖直和水平方向的位移量与草本植被边坡相比减小1.60~1.77 mm,与灌木植被边坡相比减小3.78和4.11 mm,与素土边坡相比减小7.39和6.29 mm。研究结果对防治高寒半干旱地区坡面水土流失、浅层滑坡等地质灾害,具有参考价值和指导意义。

Mechanical effects of vegetation protection on slope under loading conditions in loess areas of Xining Basin

Abstract: In order to investigate the influence of plant roots on slope stability under load conditions in the loess area of the Xining Basin, the Changlinggou watershed in the Xishan Mountains of Xining Basin was used as the experimental area in this study, the herb Elymus nutans and shrub Caragana korshinskii that suitable for the growth of the local climate environment were selected as the test species. Three planting schemes on the slope surface, i.e. single herb(Elymus nutans), shrub(Caragana korshinskii) and the combination of both were adopted. By applying a load on the top of the slopes, and disposing displacement meters and earth pressure boxes at different positions of slopes, the characteristics of soil displacement and earth pressure were analyzed. On this basis, the shear tests were carried out on the root-soil complex of slope vegetation, and the shear strength and variation characteristics of the root-soil complex at different positions of the slope under loading conditons were analyzed. The results showed that the cohesion of root-soil complex at the same position of slopes was greater than that before loading, and the cohesion of root-soil complex of three kinds of plant slopes was greater than that of slopes of soil without roots under the same conditions. Before loading, the density, moisture content and internal friction angle of the four types of slopes at the same depth below the surface did not show significant differences (P<0.05), and the density and moisture content decreased with the increase of sampling depth. The density of Elymus nutans slope, Caragana korshinskii slope, slope of soil without roots and combination planting slope at 0-10 cm below the surface was higher than that at> 20-30 cm, and the water content decreased by 21.31%, 16.13%, 19.47% and 23.04% respectively. Compared with the slope of soil without roots, the root-soil complex cohesion of the composite vegetation slope increased by 111.57%-136.50%, the herb slope increased by 69.62%-88.73%, and the shrub slope increased by 67.40%-84.27%; the root-soil complex cohesion of the composite vegetation slope was significantly higher than that of the slope of soil without roots(P<0.05). Under the loading conditions, the density, moisture content and cohesion of soil increase compared with those before loading, and the increase ranges of slope of soil without roots were 1.45%-2.80%, 1.09%-3.59% and 7.75%-9.25% respectively. The density, moisture content and cohesion of herbaceous, shrub and composite vegetation slopes increased by 0.71%-2.05%, 0.66%-9.79% and 0.65%-0.68%, 3.33%-7.55%, 4.19%-4.59% and 4.45%-8.13%, 3.79%-7.25%, 3.25%-6.95% and 2.63%-3.97%, respectively. Under the maximum loading condition, compared with the slope of soil without roots, the vertical displacement of the slope with combined vegetation, the slope with herb vegetation and the slope with shrub vegetation decreased by 58.81%, 44.80% and 28.41%, and the horizontal displacement decreased by 62.20%, 48.66% and 31.71%, respectively. The combined vegetation with herb and shrub had a greater inhibitory effects on the shallow displacement of the slope. The research results have certain theoretical research value and practical significance for the scientific and effective prevention and control of soil erosion, shallow landslide and other geological disasters in alpine and semi-arid areas.