典型黄土丘陵区浅层黄土滑坡稳定性评价——以延安市志丹县为例

黄土丘陵地区地质环境脆弱,每到雨季极易诱发浅层黄土滑坡,对居民的生命和财产安全构成威胁也阻碍着当地经济的发展。对浅层滑坡进行稳定性评价,不仅有助于认识浅层滑坡的发生发展过程,而且对防灾减灾和地区规划建设具有十分重要的指导意义。本研究选择SINMAP模型作为评价浅层黄土滑坡的重要工具,评价了陕西省延安市志丹县黄土丘陵区浅层滑坡的稳定性,评价结果表明：1）研究区整体稳定性程度较高,在降雨量为8.6 mm、15 mm、25 mm、50 mm和100 mm时不稳定区域（包括极不稳定、不稳定和潜在不稳定）面积分别占研究区总面积的9.12%、18.93%、23.17%、30.94%和38.67%,不稳定区域的面积不超过整个研究区面积的一半,极不稳定区域的滑坡密度最大,其次为不稳定区域和潜在不稳定区域;2）随着降雨量的增大,潜在不稳定和不稳定区域的面积会逐渐扩大,极不稳定区始终位于坡度大且水流侵蚀强烈的地方,变化幅度小;3）浅层滑坡的稳定性很大程度上依赖于当地的地形条件：坡度分布为20°~51°,高程分布范围为1302~1606 m,在坡向上阴坡的发生数量多于阳坡,西向和西北向浅层滑坡最为发育;4）流域内的滑坡多属降雨诱发的山体滑坡,确定性模型SINMAP为预测这一类滑坡提供了强大的工具,不仅评估了现有的已发生的滑坡的稳定性,也预测了未来在不同降雨条件下可能发生滑坡的地区。分析结果可为预防和减轻滑坡灾害带来的损失,合理的城市规划和道路选址等提供参考。

     

降雨诱发浅层黄土滑坡变形破坏机制

由降雨引发的浅层黄土滑坡灾害具有致灾性强、范围广、影响面积大等特点,是黄土高原地区危害严重的地质灾害类型。经典算法采用安全系数描述坡体稳定性,难以对坡体变形破坏的起始位置和实际失效面加以识别,限制了滑坡变形过程的描述和滑坡有效预测。以非饱和土吸应力理论为指导,基于Hydrus中的Slope Cube模块,建立黄土斜坡水-力耦合模型,结合黄土地区易滑坡形态统计数据,针对凸型、凹型、直线型3种坡型与30°、40°、50°三种坡度组合,计算了不同降雨条件下的坡体稳定性响应。结果表明,不同坡型的黄土斜坡对降雨条件具有明显的响应。相同降雨量、相同坡度条件下直线型坡发生浅表层破坏的可能性最低,凹型坡次之、凸型坡的稳定性最差。与之相对应的,相同条件下凸型坡失稳时间最短、凹型坡次之、直线型坡最长。本研究可为浅层滑坡的早期识别和预报提供支撑。     

降雨型浅层滑坡危险性预测模型

通过分析SHALSTAB和TRIGRS等浅层滑坡物理确定性模型存在的问题,提出了基于降雨入渗动态守恒的瞬态降雨入渗模型,该模型考虑了初期降雨过程、降雨历程以及饱和非饱和入渗过程,证明了SHALSTAB模型是该模型的特殊形式,并克服了TRIGRS模型参数繁多及一维入渗路径的问题.将无限边坡模型、瞬态降雨入渗模型和GIS进行耦合,研发了可用于大范围降雨型浅层滑坡危险性预测的集成系统,根据边坡的地质条件、地形参数和降雨特征即可对降雨条件下浅层滑坡的危险性进行评估.     

基于最大熵-无限边坡模型的降雨诱发浅层黄土滑坡稳定性评价方法研究

无限边坡（Sinmap）模型在评价降雨作用下浅层黄土滑坡稳定性时精度较低。针对这一问题,基于最大熵（Maxent）模型对Sinmap模型评价进行改进,构建了最大熵-无限边坡（Maxent-Sinmap）模型,评价降雨作用下区域性浅层降雨型黄土滑坡稳定性。以黄土滑坡高发区的陕西省志丹县为例,利用野外及室内相关工作获取地形、岩土体力学参数及地质灾害等相关数据,通过Maxent模型获取主要环境变量,再根据主要环境变量进行分区,通过Sinmap模型对降雨作用下不同分区的浅层黄土滑坡稳定性进行评价。研究结果表明：基于Maxent模型得到志丹县内滑坡主要受坡度、降雨量、地貌、道路缓冲区及归一化植被覆盖指数等5个指标影响,对历史灾点的贡献率分别为27.1%、20.3%、18.8%、18.7%、6.2%。相较于传统Sinmap模型,该模型不稳定区域灾点密度在小雨、中雨、大雨、暴雨和大暴雨情况下分别提高了17.26%、16.54%、17.39%、14.20%、12.96%。Maxent-Sinmap模型计算结果相较于Sinmap模型计算结果具有更大的稳定区域,且稳定区的扩大区无历史灾点分布。表明该模型具...     

降雨型滑坡危险性区划方法

降雨诱发的滑坡等地质灾害分布广、危害大,开展地质灾害危险性区划是减轻地质灾害损失的有效途径之一。以湖南省为例,根据地质灾害调查成果,选取3 412处滑坡,分析了区域降雨型滑坡的发育特点和分布规律,建立了危险性区划指标体系,利用不确定性推理中的确定性系数法,对滑坡与工程地质岩组、坡度、坡向、植被和年均降水量5个评价因子进行了相关性分析,建立了Logistic多元回归模型;采用不规则网格单元划分方法,形成了湖南省滑坡灾害危险性区划图。     

降雨诱发浅层滑坡渐进破坏分析研究

为分析降雨诱发浅层滑坡的演变过程。本文以湖南湘西古丈滑坡为例,基于Green-Ampt入渗模型,进行了降雨诱发浅层滑坡渐进破坏分析。研究结果表明:在强降雨作用下,滑坡的失稳破坏主要是由于前缘土体以及中前部土体的局部破坏,而逐渐发展为整体破坏。并且,受滑坡地形影响,地形平缓的区域虽然湿润锋下渗较快,土体抗剪强度较低,但由于土体饱和带的渗流作用较小,而重力提供垂直于滑面的分力较大,该部分稳定性较为良好,故湿润锋对于滑坡稳定性的影响还应该根据不同地形条件加以分析。渐进式滑坡破坏分析方法对滑坡的监测和防治具有重要的指导意义。     

基于Richards传导方程的降雨型浅层滑坡稳定性分析

基于描述流体在多孔介质中毛细传导行为的Richards方程,Iverson（2000）推导了斜坡中任意深度处的孔隙水压力对降雨入渗的响应方程,本文在此基础上进一步推导了降雨型浅层滑坡稳定性计算表达式。该表达式考虑了坡体非饱和区饱和度和坡体重度在降雨入渗过程中的变化。算例结果表明：降雨入渗过程中浅层滑坡稳定性系数逐渐降低,且在降雨停止后的较短时间内达到最小值,之后逐渐增大,但增大速率比降低速率要低。这种变化趋势在不同初始地下水位竖向埋深情况下是一致的,但稳定性系数随初始地下水位竖向埋深增大而减小。降雨历时和降雨入渗率对浅层滑坡的稳定性均有显著影响,表现为降雨历时和降雨入渗率越长（大）,稳定性系数降低幅度越大,但后者的影响受到滑坡体竖向渗透系数的控制。     

降雨类型对浅层滑坡稳定性的影响

在降雨与浅层滑坡稳定性关系的研究中, 目前的研究往往忽略了降雨类型的影响.因此, 选取4种具有代表性的降雨类型: 均匀型、递增型、递减型以及峰值型为对象, 基于Rosso提出的降雨强度与地下水关系模型, 构建考虑降雨类型的浅层滑坡地下水位高度随降雨时间的变化关系, 研究不同降雨类型对浅层滑坡地下水位变化的影响.进而, 结合无限边坡理论, 建立浅层滑坡的稳定性计算模型, 研究不同降雨类型对浅层滑坡稳定性的影响.研究结果表明: 降雨类型对浅层滑坡稳定性的影响是明显的, 递增型降雨作用下的浅层滑坡安全系数最小, 其次是均匀型降雨, 再次是峰值型降雨, 最大的是递减型降雨; 同时在确定浅层滑坡临界降雨量和进行区域浅层滑坡易发性研究时降雨类型的影响不容忽视.      

预设节理条件下降雨型黄土滑坡模型试验研究

中国黄土高原滑坡灾害频发,且大多与降雨有关,而节理构造是导致黄土滑坡发生的重要因素之一。为进一步揭示节理对黄土滑坡的影响作用,本文以节理为研究切入点,基于实地考察,开展了预设节理工况下降雨诱发滑坡的大型物理模型试验。通过实时监测模型边坡内部土体含水率和孔隙水压力等指标参数随降雨过程的阶段性变化,分析了边坡内部节理裂隙的扩张与演化趋势,以及坡体位移和形变特征,对比揭示了节理的存在对于诱发滑坡的潜在机制及坡体响应规律。试验结果表明：节理对雨水在坡体内部的入渗具有明显的加速和促进作用,预设节理侧的边坡相对于不含节理侧,其土体含水率增速更快、增幅更大且影响范围更广;位于模型边坡中部的节理裂隙的张开度最大,含节理侧坡体的裂隙张开度约为不含节理侧的2倍,滑坡发生时,含节理侧的孔隙水压力的上升幅度相对较大;土体含水率对降雨的敏感度和变化幅度与埋深成反比,坡体浅表部含水率的响应较快且波动较大,而深部则相反。研究结果可为进一步厘清黄土滑坡的成因及破坏机理提供试验依据和理论参考。     

降雨条件下浅层滑坡稳定性探讨

降雨条件下浅层滑坡是一种常见、多发的地质灾害现象,为了解边坡稳定性随降雨入渗过程的变化情况,以Green-Ampt入渗模型为基础,并考虑了动水压力的作用,建立了降雨入渗条件下浅层滑坡的概念模型,分别推导了降雨前有、无地下水位条件下的边坡安全系数与降雨时间的关系表达式。从分析结果中可以看出,对于这两种情况下边坡稳定性发生突变的主要原因归结于：前者为在湿润锋与地下水位面接触的短时间内,滑带处的孔隙水压力迅速增高;后者为滑带在浸水饱和情况下,岩土体的强度迅速降低。在此基础上,根据降雨过程中边坡是否达到饱和,提出边坡饱和临界时间的概念,考虑了初始降雨强度小于土壤入渗能力的情况。这个时间可以作为一个参数指标用于浅层滑坡的预警。     

Susceptibility assessment of shallow landslides triggered by rainfall in tropical basins and mountainous terrains

Natural Hazards - This study presents the analyses and results of the implementation of the SHALSTAB model to study landslides caused by rainfall that occurred on September 21, 1990, in a basin of...     

A loess landslide induced by excavation and rainfall

The initiation of loess landslides is a common engineering problem during the construction of the expressway or other engineering works in the Loess Plateau of China. The engineers and researchers should devote themselves to the prevention of the initiation of loess landslides. This study focused on a loess landslide which was induced during the construction of an expressway in Shanxi Province of China. The stabilities of the loess hillside slope before and after excavation were analyzed using limit equilibrium analysis method and the strength reduction finite element method, respectively. The analysis results indicated that the loess hillside slope, before excavation, was stable under both natural state and rainfall conditions. The collapse of the loess hillside slope, or the initiation of loess landslides, after having been excavated, was induced by excavation and rainfall. The integrated stabilization method including four parts was used to stabilize the loess landslide. The four parts were a reinforced concrete piles row, a rubble concrete retaining wall, alteration of slope geometry, and interception and drainage of water. The initiation of the loess landslide might be evitable if it was given enough attention before excavation; thus, the problem of loess landslides should be paid big attention during the survey and design of the engineering works, not only during the construction.     

窑洞开挖诱发浅层黄土滑坡的变形机理模拟

由废弃窑洞倒塌引发的黄土边坡失稳严重威胁了黄土高原地区居民的生命财产安全。通过野外调查,选取陕西省延安市三亩台滑坡为典型案例,基于室内试验分析了窑洞废弃、依窑建房等工况下黄土含水量和土体强度的变化规律,运用数值模拟研究了窑洞废弃、依窑建房过程中最危险滑面上的应力和强度变化趋势。从土体应力-强度关系角度揭示了废弃窑洞诱发黄土边坡变形破坏机理。研究表明,窑洞废弃和依窑建房增大了土体含水量,降低了土体的抗剪强度,致使坡体下部土体剪应力逐渐接近其抗剪强度,边坡的稳定性随之降低,最终窑洞坍塌引发滑坡。     

Effects of degree of saturation on shallow landslides triggered by rainfall

The empirical rainfall threshold concept and the physical-based model are two commonly used approaches for the assessment of shallow landslides triggered by rainfall. To investigate in detail the rainfall-triggered shallow landslides, many physical-based models coupling the infinite slope stability analysis with the rainfall infiltration modeling in variably saturated soil were developed. However, in those physical-based shallow landslide models, the unit weight and the unsaturated shear strength were assumed constant rather than depending on the degree of saturation. In this study, the effects of the unit weight and the unsaturated shear strength as function of degree of saturation on rainfall-triggered shallow landslides are examined. Several designed scenarios and a real case scenario are used to conduct the examinations. The results show that not only the occurrence of shallow landslides but also the failure depth and the time to failure could be misassessed if the influences of degree of saturation on the unit weight and the unsaturated shear strength are neglected.     

区域崩塌滑坡的易发性评价--以四川省珙县为例

以四川省珙县为例，探讨了以GIS技术为支撑的区域崩塌、滑坡易发性评价的基本思路和技术路线；对评价指标的选取作了概括的分析和说明，认为其预测评价因素分为基本因素和诱发因素2大类；采用模糊综合评判方法对崩塌、滑坡的易发性进行评价，并在模糊综合评判方法的具体应用、评价指标隶属度的确定以及权重确定等方面也作了分析和阐述；对珙县区域崩塌、滑坡的易发程度讲行了评价，结果与实际较为吻合。     

甘肃黑方台地区灌溉型黄土滑坡形成机理 与运动学特征 ——以焦家崖头13号滑坡为例

甘肃黑方台地区常年农业灌溉导致塬边产生大量的黄土滑坡,灌溉水长期入渗引起灌区地下水位上升,因地下水作用造成水敏性黄土遇水乃至饱水后强度劣化,进而产生斜坡失稳,因黄土滑坡剪出口高悬于上缓下陡的坡体中部,其成灾模式呈现出高位剪出后高速滑动,并产生远程运移,波及范围大,致灾后果严重。以甘肃省永靖县黑方台焦家崖头滑坡为例,在现场调查和地下水动态监测的基础上,对灌溉型黄土滑坡塑流-拉裂形成机理进行分析,并运用离散元模拟方法,对地下水位上升过程中模型底部饱水黄土软弱层的形成、演化过程和滑坡运动学特征进行模拟研究。结果表明,随地下水位的上升,模型底部软弱层范围不断增大;孔隙水压力主要作用于滑坡底部软弱层饱水黄土;地下水位高程上升至标高1682m时,滑坡产生整体破坏。     

Study of shaking table test of seismic subsidence loess landslides induced by the coupling effect of earthquakes and rainfall

Light rain or moderate rain is the most common meteorological event in the rainy season in the loess area of China, so the probability of landslide hazards induced by the coupling effect of earthquakes and rainfall under the condition of light rain or moderate rain is relatively higher than that under heavy rain. To study the dynamic response characteristics and instability mechanism of loess slopes by the coupling effect of earthquakes and rainfall under the conditions of moderate rain and light rain, a low-angle slope model test of a large-scale shaking table after 10 mm of rainfall was carried out. By gradually increasing the dynamic loading, the evolution of the macroscopic deformation and the instability failure mode of the slope model are observed; the temporal and spatial trends of the amplification effect, acceleration spectrum, pore pressure and soil pressure are analyzed; and the failure mechanism of the slope is determined. The results showed that the amplification effect increased along the slope surface upward, and a strong amplification effect appeared at the front of the top of the slope. Because of the stronger dynamic stress action on the upper part of the slope, the immersed soil in the upper part of the slope experienced seismic subsidence deformation, the saturation in the seismic subsidence soil increased, and the water content temporarily increased locally. With the further increase in the loading intensity, a large number of tension cracks were generated in the seismic subsidence area, and water infiltrated down along the cracks and the wetting range expanded under dynamic action. The range of seismic subsidence and cracks further extended to the deep part of the slope. Under the reciprocating action of the subsequent ground motion, the swing amplitude of the soil mass in the seismic subsidence area, which is divided by a large number of cracks in the upper part of the slope, increased further, resulting in the further reduction in the residual strength of the seismic subsidence soil mass located at the crack tip due to the pull and shear action. Finally, under the combined action of gravity and dynamic force, the upper soil mass in the seismic subsidence area dragged the lower soil mass in the seismic subsidence area downward because the sliding force is greater than the residual strength of the soil mass, which induced a seismic subsidence-type loess landslide. Under the coupling effect of earthquakes and rainfall, the instability mode and mechanism of this landslide are significantly different from those of liquefaction-type landslides.

     

汶川地震中甘肃清水田川黄土液化的试验研究

2008年5·12特大地震中,位于甘肃省清水县郭川乡的田川村发生了饱和黄土的液化滑移灾害。本文首先在对田川场地进行考察的基础上,综合田川在汶川地震中的震害情况以及滑移区的地形条件,将该地区在汶川地震中的烈度进行了修正。其次对田川黄土进行了物性指标测试以及室内动三轴液化试验,根据试验结果,综合考虑产生液化所需的场地及土性条件、黄土的动强度和液化特性,对田川黄土液化灾害进行了分析,并采用反应分析的方法对其进行了液化判定。研究结果证明了田川黄土液化的事实存在性,为低烈度区黄土液化提供了新的震害依据。