青藏高原东北部黄土区灌木植物根系护坡效应的数值模拟

为研究青藏高原东北部黄土地区灌木植物根系与边坡稳定性之间的关系,以试验区西宁盆地及其周边黄土边坡为例,选取适合于研究区生长的柠条锦鸡儿、四翅滨藜、霸王及白刺4种灌木进行坡面种植,并对其根–土复合体进行力学强度试验,且采用二维有限元法模拟试验区生长期为2a的4种灌木植物根系对边坡稳定性的增强作用。试验和模拟结果表明:试验区种植4种灌木植物的坡体,其水平方向和垂直方向的位移显著小于素土边坡,相比较而言,种植4种灌木植物的坡体所发生的水平和垂直最大位移量相对由小至大的顺序依次为柠条锦鸡儿、四翅滨藜、霸王及白刺;4种灌木植物其侧根和主根在土体中分别起到加筋和锚固作用,这种根–土相互作用增加了坡体的黏聚力和抗剪强度,从而使试验区边坡应力集中范围缩小,塑性破坏区面积减小。试验区边坡安全系数计算结果表明,与素土边坡相比,试验区四翅滨藜、柠条锦鸡儿、霸王、白刺根–土复合体边坡相对稳定安全系数依次增强80.5%,48.7%,22.1%和8.0%。由此说明试验区4种灌木植物其护坡贡献大小依次为柠条锦鸡儿、四翅滨藜、霸王及白刺。研究成果可作为青藏高原东北部黄土区采用优势护坡灌木植物,防治坡面浅层滑坡、崩塌、泥石流等地质灾害发生的理想依据之一。

NUMERICAL SIMULATION OF SHRUB ROOTS FOR SLOPE PROTECTION EFFECTS ON LOESS AREA OF NORTHEAST QINGHAI-TIBETAN PLATEAU

To study the relationship between shrub roots and slope stability in loess area of northeast Qinghai— Tibetan plateau，four shrubs Caragana korshinskii，Atriplex canescens，Zygophyllum xanthoxylon and Nitraria tangutorum were planted on the slopes of the test area in Xining basin. The mechanical strength tests of root-soil composite systems were carried out and the increasing effect of slope stability of four two-year growth shrubs were simulated with two-dimensional finite element method. The results show that the horizontal and vertical displacements of four shrubs root-soil composite systems are obviously smaller than those of soil without roots. The order of four two-year growth period shrubs in the course of deformation in magnitude is Caragana korshinskii，Atriplex canescens，Zygophyllum xanthoxylon and Nitraria tangutorum. Lateral roots and main roots of shrubs play a part in reinforcement and anchorage in the soil，which increase the shear strength and the cohesion of the soil，thus the plastic area and the shearing stress concentration area can be reduced. The results of factors of safety of the slope in the testing area show that，compared with the safety factor of soil without roots，the increments of the safety factor of the related slope of the four shrubs root-soil composite systems of the four shrubs are 80.5%(Atriplex canescens)，48.7%(Caragana korshinskii)，22.1%(Zygophyllum xanthoxylon) and 8.0%(Nitraria tangutorum)，respectively. The achievements can be taken as criteria for choosing shrubs for protecting slope and preventing shallow landslide，collapsing and debris flow in loess area of northeast Qinghai—Tibetan plateau.