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黄河上游沙漠小流域粗沙岸坡重力侵蚀特性的数值模拟

Numerical Simulation of Gravity Erosion Characteristics of Coarse Sand Bank Slope in Desert Small Watershed of Upper Yellow River

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【Author in Chinese】 张科

【Supervisor】 郑健王之君

【Author's Information】 兰州理工大学, 水利水电工程, 2020, 硕士

【Abstract in Chinese】 黄河上游“十大孔兑”流域沙漠粗沙岸坡在暴雨洪水侵蚀作用下发生重力滑塌,以高含沙洪水形式入汇干流,是宁蒙河段粗泥沙的重要来源之一,由此产生的泥沙灾害问题严重影响黄河上游生态系统稳定与黄河健康。本文选取“十大孔兑”最西端毛不拉孔兑之典型支沟“苏达尔沟”沙漠小流域为研究区域,以野外观测、室内试验及数值模拟为主要研究手段,探索沙漠粗沙岸坡重力侵蚀滑塌过程与型态的力学机制,并与黄土岸坡滑塌特性进行对比分析,取得主要研究结果如下:(1)通过野外调研与采样分析,遴选粘聚力、内摩擦角及地下水位等三因素为影响岸坡滑塌的主要因素,进行数值模拟敏感性分析,结果表明:黄河上游“十大孔兑”地表物质组成由粗沙向黄土过渡过程中,随着土体粘聚力、内摩擦角的增大,岸坡稳定性逐渐增强,随着地下水位的上升,岸坡稳定性却逐渐减弱。岸坡稳定性对粘聚力的变化最敏感,其次是内摩擦角、地下水位。(2)基于Abaqus数值模拟软件,以粘聚力主要参数,开展岸坡滑塌过程的数值模拟,结果表明:粘聚力主要通过控制岸坡土体出现塑性变形时间、完全失稳时间来影响岸坡的稳定性。粘聚力越大,岸坡土体出现塑性变形及完全失稳所需时间越久,岸坡土体的稳定性也越强;岸坡失稳的最危险部位,主要集中在坡脚处,坡脚水流侧向掏蚀作用,对岸坡滑塌,起到了重要的加速作用。(3)采用GEO5岩土工程数值模拟软件,通过渗透系数测定、颗粒级配分析等室内试验率定模型参数,分别就研究区粗沙与黄土岸坡开展滑塌型态的数值模拟,结果表明:受土体颗粒之间粘聚力的影响,粗沙岸坡主要表现为分层、片状滑塌,而黄土岸坡多表现为块状或团状滑塌;较之黄土岸坡的弧型滑动,粗沙岸坡为折线型滑动,滑塌型态直立,模拟与实测结果定性吻合。研究成果对下一步耦合坡脚水流掏蚀作用等因素,定量估算侵蚀滑塌量,揭示侵蚀滑塌机制,建立符合真实物理图景的高含沙洪水侵蚀产沙数学模型,进而丰富干旱区土壤侵蚀理论体系而言,具一定的科学意义,对于指导沙漠流域水土保持综合治理,具有重要的实践指导价值。

【Abstract】 The desert coarse sand bank slope in the "ten tributaries" watershed gravitycollapsing due to the erosion of rainstorm flood,pouring into the Yellow River in theform of hyper-concentrated flood.It is one of the important sources of coarse sand inthe Ningmeng reach.The sediment disaster seriously affects the stability of theecosystem and the health of the Yellow River.In this paper,the typical tributary"Sudalaer" desert small watershed was selected as the research area,and fieldobservation,laboratory tests and numerical simulation were used as the main researchmethods to explore the mechanical mechanism of gravity erosion and slump processand types of desert coarse sand bank slope,and to make a comparative analysis withloess bank slope slump characteristics.The main research results were as follows:(1)Through field investigation and sampling analysis,three factors including cohesion,internal friction angle and underground water level are selected as the main factors affecting bank slope slump,and sensitivity analysis is carried out by numerical simulation.The results showed that during the transition process from coarse sand to loess in the "ten tributaries" surface material composition in the upper reaches of the Yellow River,the bank slope stability gradually increasing with the increase of soil cohesion and internal friction angle,while decreasing with the increase of underground water level.The stability of bank slope was most sensitive to the change of cohesion,followed by internal friction angle and groundwater level.(2)Based on Abaqus numerical simulation software,the numerical simulation of bank slope collapse process is carried out with the main parameters of cohesion.The results show that cohesion mainly affects the stability of bank slope by controlling the time of plastic deformation and complete instability of bank soil.The greater the cohesion,the longer the plastic deformation and complete instability of the bank soil,the stronger stability of the bank soil.The most dangerous part of bank slope instability is mainly concentrated at the foot of the slope.The lateral erosion of water flow at the foot of the slope has played an important accelerating role in bank slope collapse.(3)GEO5 geotechnical engineering numerical simulation software is used to calibrate the model parameters through laboratory tests such as permeability coefficient determination and particle gradation analysis.The numerical simulation of slump types is respectively carried out on coarse sand and loess bank slope in the study area.The results show that due to the cohesive force coarse sand bank slope is mainly layered and flaky slump,while loess bank slope is lumpy slump.Compared with the curved sliding of loess bank slope,the coarse sand bank slope is broken-line sliding,and the sliding type is vertical.The simulation results are qualitatively consistent with the measured results.The research results have certain scientific significance for the next step of coupling factors such as erosion of slope toe water flow,quantitatively estimating the amount of erosion slump,revealing the mechanism of erosion slump,establishing a mathematical model of sediment yield due to hyper-concentrated flood erosion in line with the real physical picture,and further enriching the theoretical system of soil erosion in arid areas,and have important practical guiding value for guiding the comprehensive management of soil and water conservation in desert basins.

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