【作者】 马建全；

【导师】 李广杰；

【作者基本信息】 吉林大学 ， 地质灾害防治工程， 2012， 博士

【摘要】 黄土滑坡，作为一种地质灾害，它与洪涝、飓风等自然灾害一样，可掩埋村庄、农田、摧毁工厂、中断交通、堵塞河流、造成人员伤亡等，给国家和人民生命财产、经济建设带来巨大的损失。尤其是近年来，黄土台塬区因农业灌溉而触发的滑坡正引起公众、各大媒体和工程地质界的重视。因此研究灌溉诱发型黄土滑坡的形成条件、形成机理及其稳定性，揭示该类滑坡孕育、发展直至消亡的过程，具有重要的理论意义和现实价值。本文以甘肃省永靖县黑方台台塬缘边黄土滑坡为研究对象，在系统归纳总结灌溉诱发型黄土滑坡研究现状基础上，通过收集、整理大量文献资料，分析了研究区的地质环境背景和滑坡灾害特征；利用计算机数值模拟手段研究灌溉渗透过程中地下水运移规律，从而分析探讨黄土边坡稳定性与灌溉渗透过程中地下水的相互关系；利用颗粒流(PFC2D)数值模拟软件对黑方台焦家崖头的黄土滑坡运动过程进行了模拟。论文研究取得了以下主要结论：1)研究区已发现的35处滑坡，主要是黄土滑坡和黄土-基岩滑坡，以黄土滑坡发育数量最多为主，且大部分是不稳定的中型浅层新滑坡；黄土-基岩滑坡发育数量少，但其规模较大，大部分是较稳定的大型深层新滑坡。划分出了6种平面形态类型和2种纵断面形态类型。从滑坡坡长、坡高、坡宽、坡度、主滑方向等，描述并总结了滑坡外形发育特征。从滑坡后缘、前缘发育特征分别总结了黄土滑坡和黄土-基岩滑坡的边界特征。对滑坡变形及运动特征提出了4个变形过程及2种运动形式。2)对灌区黄土层地下水的补给条件及排泄方式进行了分析，并在此基础上建立了水文地质概念模型及数学模型，利用FEFLOW进行了灌区地下水三维非饱和非稳定流数值模拟，分析结果可知：随着年灌溉量的不同，地下水分布情况有所不同，但总的趋势是地下水水位随着灌溉量的增加而升高，地下水由西向东流动，由东部台缘及两侧向外排泄；台塬中心黄土层饱水带厚度也是随灌溉量逐渐在增加的，厚度由中心向四周逐渐变薄；不同灌溉条件下，台塬不同位置地下水位变化幅度及水位上升幅度也有所不同，在灌溉的头5年间，地下水位上升最快，其后地下水渗流场趋于稳定流动，地下水变化幅度不仅和灌溉量的大小有关，而且和其所在地的位置有关系；依据监测点数据，找寻到了灌溉量与地下水位上升幅度的关系曲线。3)在已有地下水运移规律研究的基础上，针对研究区滑坡灾害发生机制，提出了考虑非饱和抗剪强度及渗透力的极限平衡方法，从8个方面对其进行了研究，并详细地推导了稳定系数计算公式。采用MATLAB语言对该方法进行编程使其程序化，编制了基于非饱和抗剪强度理论及渗透力的斜坡稳定性评价程序(PUSG)。4)选取黑方台焦家崖头的典型斜坡为例，设计了一系列计算方案，考虑不同工况下(不同年灌溉量下地下水位工况)的不同的评价方法(传统极限平衡法、基于非饱和抗剪强度及渗透力的极限平衡法)，采用PUSG程序对其进行斜坡稳定性计算。对比两种方法计算结果，随着年灌溉量的增大，斜坡稳定系数呈递减趋势，但地下水位对计算结果的影响程度不同，传统极限平衡法的稳定系数计算结果显示，随着年灌溉量的增大，稳定系数从1.045降低到1.003，斜坡稳定系数均大于1，且小于1.1，表明斜坡为欠稳定状态，处于蠕动-拉裂阶段，地下水位对斜坡稳定性计算影响不明显。基于非饱和抗剪强度及渗透力的极限平衡法的稳定系数计算结果显示，随着年灌溉量的增大，稳定系数从1.283降低到0.796，当年灌溉量大于500×104m~3时，斜坡稳定系数均小于1.1，表明斜坡处于欠稳定或不稳定状态。因此，年灌溉量500×104m~3为一个界限值，即斜坡稳定年灌溉量界限值，当年灌溉量小于这个界限值时，该斜坡将处于稳定状态，当年灌溉量大于这个界限值时，该斜坡将处于不稳定状态，地下水位对斜坡稳定性计算影响较为显著。5)结合研究区滑坡变形特征及运动特征，利用颗粒流(PFC2D)数值模拟软件，对黑方台焦家崖头黄土滑坡“软化潜蚀”阶段、蠕动-拉裂阶段、滑动-破坏阶段和稳定-压密阶段4个阶段的运动过程进行模拟，并对模拟结果进行分析，再现黄土滑坡从变形、破坏到消亡的运动过程。更多还原

【Abstract】 Loess landslides, as a kind of geological disasters, be similar to floods, hurricanes and othernatural disasters. It has brought a huge loss to people’s lives and property and the nationaleconomic construction, such as buried villages and farmlands, destroyed plants, interruptedtraffic, blocked rivers, and caused casualties, etc. In recent years, landslides of the Loess Plateautriggered by agricultural irrigation is attracting the attention of the public, the media andengineering geological community. Therefore, it has important theoretical significance andpractical value to study the formation conditions, formation mechanism and stability ofirrigation-induced loess landslides, and to reveal the landslides how to nurture, how to developuntil the landslides die out.In this paper, we focus on the landslides of the Heifangtai loess platform in YongjingCounty, Gansu Province. First of all, through summarized the research status ofirrigation-induced loess landslides and collected large number of documents, the geologicalenvironmental background and the characteristics of the landslide hazard are analyzed. Secondly,researching the groundwater migration law in the irrigation process by computer numericalsimulation based on indoor and outdoor test data. And the relationship between the slope stabilityand irrigation infiltration process was analyzed. The process of four movement stages of loesslandslide was simulated using PFC2Dsoftware. The main conclusions as follow:1)35landslides have been found in the study area, mainly loess landslides andloess-bedrock landslide. Large numbers of landslide are loess landslides and primarily are theunstable medium-sized shallow landslides. Small numbers of landslide are loess-bedrocklandslides and usually are the more stable large-scale deep landslides. Six kinds ofcross-sectional shape types and two kinds of longitudinal shape types are proposed. Thedevelopment characteristics of landslide shape are described and summarized from length, height,width, slope, the main slip direction and so on. The boundary feature of loess landslides andloess-bedrock landslides are summarized from the development features of landslide trailingedge and landslide front edge. Four kinds of deformation process and two kinds of movement patterns are proposed.2) Groundwater recharge and discharge in loess formation were analyzed, and on this basis,the hydro-geological conceptual model and mathematical model were established.Three-dimensional groundwater unsaturated flow in irrigation area was simulated by FEFLOWsoftware. The analysis of results shows that: with the different annual irrigation amount, thedistribution of groundwater was unlike. However, the overall trend is that the groundwater levelwas increased with the increasing annual irrigation amount; groundwater flow was from west toeast; water was excreted in the eastern platform margin and on both sides. The saturated zonethickness of center layer of the loess platform is gradually increasing with the increasing annualirrigation amount, and progressively becomes thinner thickness from the center to thesurrounding. Under different irrigating schemes, the change rates of groundwater level wereunlike in certainly platform locations. In the first five years of irrigation, groundwater levelraised the fastest, and groundwater seepage was tended to a steady flow with increasingirrigation time. The change rates of groundwater were not only with the annual irrigation amount,but also with the location in loess platform. According to the data of the monitoring points, therelationship curve was obtained between the annual irrigation amount and the change rates ofgroundwater level.3) Base on the mechanism of landslide formation and the research of groundwater migrationlaw in study area, unsaturated shear strength and seepage force of the general limit equilibriummethod was proposed. Then it was researched from eight aspects, and the computing formulas ofthe stability factor were derived in detail. Unsaturated shear strength and seepage force of thegeneral limit equilibrium method was programmed by the MATLAB language, and a slopestability assessment procedure was accomplished.4) Take a typical slope of the Heifangtai loess platform in study area as an example. UsingPUSG program the slope stability was calculated with a series of the designed calculationscheme, for instance, taking into account different conditions (under different in the amount ofirrigation), taking into account unlike evaluation methods (traditional limit equilibrium method,unsaturated shear strength and seepage force of the general limit equilibrium method). Contrastthe results obtained by the two methods and concluded that with the increase of annual irrigationamount, slope stability factor showed a decreasing trend, but the impact of groundwater on theresult is different. The calculated results of the stability factors based on the traditional limitequilibrium method show that with the increase of annual irrigation amount, stability factor decreased from1.045to1.003, the slope stability factor greater than1and less than1.1,indicating that the slope is in an unstable state and in creep-tensile stage, and the groundwaterwas a little impact on slope stability calculation. The calculated results of the stability factorsbased on the unsaturated shear strength and seepage force of general limit equilibrium methodshow that with the increase of annual irrigation amount, stability factor decreased from1.283to0.796. When the annual irrigation amount is greater than500×104m3, the slope stability factorsare less than1, indicating that the slope is in an unstable state. Therefore, the500×104m3is alimit value, which we called the limit value of the annual irrigation amount of slope stability.When the annual irrigation amount is less than the limit value, the slope will be in the stable state.In other words, when the annual irrigation amount is larger than the limit value, the slope will bein an unstable state. The groundwater was a relatively large impact on slope stability calculation.5) Combined with the characteristics of loess slides’s deformation and movement inresearch area, using PFC2Dsoftware to simulate the process of four movement stages of loesslandslide, such as, soften-erosion stage, peristalsis-tensile stage, sliding-failure stage,stable-compacted stage, and the simulation results are analyzed. It is a reproduction for the entireprocess of loess landslides from the deformation, damage to the demise.更多还原