堰塞坝漫顶溃坝离心模型试验研究

基于唐家山堰塞坝坝料级配曲线,建立相应的物理模型,开展堰塞坝漫顶溃坝离心模型试验,并推导离心场下矩形薄壁堰堰流计算方法。详细分析了堰塞坝漫顶溃坝过程及溃决机理,同时根据试验得出的堰塞坝溃口流量及溃口顶宽发展过程曲线,对溃决机理研究结果做出进一步验证。结果表明:堰塞坝漫顶溃坝过程中,溃口横向扩展贯穿始终,由于大粒径颗粒在下游坝坡的残留,溃口下切发展停止时间较早,溃坝后期下游坝坡存在明显的粗化现象,且堰塞坝溃坝后较少出现全溃的情况,一般都存在一定的残留坝高,其最终溃口尺寸也应小于相同条件下的均质土坝。     

堰塞坝漫顶溃决离心模型试验研究

基于南京水利科学研究院400g·t溃坝离心模型试验系统，利用其高速旋转产生的超重力场的“时空放大”效应，开展离心模型试验研究了堰塞坝漫顶溃决时的溃口演化规律和溃决机理。首次通过离心模型试验研究了坝高、下游坡比、坝料级配对堰塞坝漫顶溃坝过程的影响。试验结果表明：堰塞坝漫顶溃坝过程可划分为表层冲刷、溯源冲蚀、沿程侵蚀和溃口稳定4个阶段；溃口峰值流量对坝高最为敏感，平均粒径次之；达峰时间主要受下游坡比影响，溃坝后相对残余坝高主要受平均粒径影响。     

黏土心墙坝漫顶溃决数值模型研究

国内外针对土石坝漫顶破坏机理和溃决过程开展了大量的研究工作,但针对黏土心墙这一土石坝主要坝型溃决机理及溃决过程的研究工作却开展的很少。研究提出能合理模拟黏土心墙土石坝漫顶破坏溃口发展时变过程数值计算模型对准确模拟黏土心墙坝溃决过程,正确评价其溃决致灾后果十分必要。从黏土心墙坝结构特征出发,根据实际溃坝调查和室内、现场溃坝试验资料,分析了黏土心墙坝漫顶溃决机理,在此基础上建立了一个描述黏土心墙坝溃口发展过程的数值模型。该模型较好地考虑了漫坝水流对下游坝壳冲蚀过程中黏土心墙滑动或倾覆失稳所引起的溃口间歇性增大现象。最后利用已发生溃决心墙坝的溃坝洪水资料验证了建议数值模型的合理性。     

混凝土面板砂砾石坝漫顶溃坝模型研究

基于沟后面板砂砾石坝溃坝案例调研资料及溃坝离心模型试验的反馈分析,提出了一个可描述混凝土面板砂砾石坝漫顶溃决过程的数学模型。该模型的特点是选择可反映高速水流作用下推移质与悬移质运动的坝料输移公式描述宽级配砂砾料的运动特征,以及建立可模拟面板坝每块钢筋混凝土面板在各种变化荷载作用下破坏过程的表达式。选择沟后面板砂砾石坝溃坝案例对建立的模型进行验证,计算结果与实测结果的对比表明:溃口峰值流量、堆石体溃口的顶宽与底宽、折断的面板的数量和各面板的破坏长度、溃坝历时等输出参数的相对误差均控制在±15%以内;由于溃坝过程中面板不断折断,溃口流量过程呈锯齿状抬升。另外,参数敏感性分析的结果表明坝料的冲蚀率和级配特征对溃坝流量过程具有重要的影响。     

土石坝漫顶溃坝过程离心模型试验与数值模拟

利用溃坝离心模型试验系统,分别对3种不同坝高均质土石坝（最大坝高达32.0 m）及坝高为16.0 m的黏土心墙坝开展了漫顶溃坝试验研究,清楚地揭示了其溃决机理、溃口发展规律。结果发现,对于均质土石坝,随着坝高的增加,溃口的纵向下切与溃口边坡的失稳坍塌速度明显加快,溃口流量过程线更为陡峭,峰值流量增大,且峰值流量出现时间更早,溃坝历时更短;黏土心墙坝与均质坝溃决机理与溃口发展规律明显不同,随着漫坝水流对下游坝壳冲蚀程度的增加,黏土心墙发生剪断破坏,溃口洪水流量迅速增大。基于上述试验结果,分别提出了描述均质土石坝和黏土心墙坝溃坝过程和计算溃坝洪水流量过程的数学模型,并建议了相应的数值计算方法。数值模拟与试验结果的对比证明了建议溃坝数学模型的合理性。     

不同密实条件的滑坡堰塞坝漫顶溃决实验

为研究密实条件对堰塞坝漫顶侵蚀机制的影响,采用室内水槽实验对松散和密实2种状态下的滑坡堰塞坝漫顶溢流破坏过程进行了模拟。结果表明,密实条件对漫顶侵蚀过程有重要影响:松散状态下,堰塞坝的侵蚀过程主要包括面冲刷–冲沟–下蚀–侧蚀等阶段,溯源侵蚀效果不明显,溃决尾声阶段出现沙垄,溃口流量上涨和消退速度快,峰值流量和总输沙量均大于密实状态并且溃口的横向扩展模式为溃口边坡的剪切滑动;密实状态下,堰塞坝会出现陡坎、冲蚀坑等侵蚀过程,溯源侵蚀效果明显,陡坎效应导致溃口水流由非堰流形式—宽顶堰流—实用堰流转化,多级陡坎合并后,溃口水流在陡坎底部产生反向旋流,加速坝体的破坏,溃口横向扩展模式为边坡土体的重力崩塌。     

单向侧蚀与下蚀共同作用下堰塞坝的演化特征

滑坡堰塞坝溃决破坏过程中均存在下蚀效应,但因堰塞坝的形成机制以及沟谷地形的限制,很多堰塞坝在横向存在高差,导致堰塞坝漫顶溃决过程中的侧向侵蚀方向为单向侵蚀。通过模型实验和数值分析,对堰塞坝在单向侧蚀与下蚀效应共同作用下的演化特征进行研究。实验结果表明,对于组成物质完全位于沟谷内的堰塞坝,单向侵蚀与下蚀效应导致堰塞坝漫顶侵蚀过程中的溃口边坡失稳规模逐渐增大。而对于横向高差悬殊的大型堰塞坝,在溃口水流的单向侧蚀与下蚀效应共同作用下,溃口边坡高度逐渐增大最终将导致堰塞坝发生二次滑坡,并采用数值方法对二次滑坡的形成过程进行分析。根据土力学理论,提出圆弧滑动模型对二次滑坡的滑动半径以及滑动面积进行预测,模型的计算值与理论值相差6.2%,具有一定的实用性。     

基于大型数据库的堰塞坝特征统计分析与溃决参数快速评估模型

21世纪以来地质灾害频发形成大量堰塞坝。然而由于缺乏详细的资料,现在对堰塞坝特征和溃决等方面的研究受到很大的制约。同时,绝大部分堰塞坝寿命极短且勘察条件恶劣,很难在短时间内获取详细的坝体参数,因此急需基于有限的可用数据进行堰塞坝溃决参数快速评估。收集国内外1 298例堰塞坝案例,对堰塞坝的分布、诱因、寿命、溃决模式、坝高、库容、成因等特征进行统计分析。通过对41例具有详细溃决信息的案例进行分析,建立坝体溃决参数(峰值流量、溃口尺寸、溃决时长)的快速评估模型,并将模型应用于唐家山堰塞坝的溃决分析。最后,基于大量案例数据进行堰塞坝模型和人工土石坝模型应用的对比分析,发现将人工坝模型用于堰塞坝会得到偏危险的结果,进而可能导致非常保守的决策和不必要的经济损失。该研究对于全面了解堰塞坝特征,尤其是对堰塞坝溃决参数评估和应急管控有一定的理论和实际价值。     

混凝土面板砂砾石坝漫顶溃决过程数值模拟

基于混凝土面板砂砾石坝溃决机理,提出了一种模拟其漫顶溃决过程的数值计算方法。该方法针对砂砾石料级配范围宽,最大颗粒与最小颗粒粒径相差大的特点,引入与水流方向垂直的附加作用力来考虑粗颗粒对细颗粒的阻拦、遮蔽以及细颗粒对粗颗粒的包围、填实等作用,导出了能较为合理反映砂砾石料特性的临界起动流速;建议了一个砂砾石料的冲蚀公式,给出了面板折断时间与坝体冲蚀量之间的数学表达式,较为合理地确定面板的折断时刻。利用该方法对青海省沟后水库面板砂砾石坝的溃决过程进行了模拟计算,得出的溃口发展规律与溃坝洪水流量过程与溃坝调查结果大体相符,验证了其合理性。     

不同底床坡度下的堰塞坝溃决过程研究

针对缺乏底床坡度对堰塞坝溃决过程影响的现状,采用7种底床坡度(1°,2°,3°,7°,9°,11°,13°)进行堰塞坝溃决试验,结果表明:不同底床坡度条件下的堰塞坝溃决过程分为3个阶段,其中第I阶段溃口发展缓慢,在背水坡形成明显的水流坡折点,第II阶段溯源侵蚀强烈,溃口快速下切和展宽,溃口类似于梯形,第III阶段水沙运动减弱并趋于平衡。峰值流量与底床坡度呈非单调关系,其随底床坡度的增大先增大后减小。当底床坡度较小时,溯源侵蚀是溃口下切的主要动力;随底床坡度逐渐增大,牵引侵蚀对溃口纵向和横向发展的作用增大。溃口宽度与深度之比随底床坡度的增大先增大后减小,且以3°为分界值。溃决后的溃口宽深比随底床坡度的增大呈先趋于1,后渐小于1的规律。     

Breaching Failure of a Huge Landslide Dam Formed by the 2005 Kashmir Earthquake

On February 9 2010, the landslide dam formed in the Kashmir earthquake that occurred on Oct 8 2005 at Hattian Bala in Pakistan was breached after incessant rains. The authors had been involved in a research project to monitor the long-lasting change of the landslide mass at regular 6 monthly intervals since June 2008, and they noticed that air-exposed pieces of sandstones and mudstones of the landslide mass had disintegrated and crumbled due to slaking that dated back to the breach. The change in the landslide mass shape observed between June 2008 and November 2009, did not seem so significant except for a 300 m-long gulley that appeared all of a sudden at the toe of the mass during winter time from 2008 to 2009. Displacements from GPS-measurements conducted in June and November 2009 showed that the crest part subsided by about 10 cm while the toe part heaved slightly up where the overflowed water fell into the eroded gully. A field survey was conducted over the breached landslide dam in April 2010, two months after the breaching event. A severely eroded breach channel was observed along the spillway, which was excavated immediately after the formation of the dam. Given the chronological change in precipitation of the catchment area of Hattian Bala obtained from the TRMM (Tropical Rainfall Measuring Mission) satellite data, the dam is considered to have been breached due to the overtopping of water over the landslide mass of slakable nature. The slakable nature of the material is discussed through both standard slaking tests and advanced unconventional direct shear tests on prepared specimens. Significant creep deformation and a reduction in their peak strength were observed as the slaking developed in the specimens, suggesting that the slakable nature of the mudstones might have been responsible for the breach of the landslide dam.     

堰塞坝泄流槽断面型式离心模型试验研究

基于唐家山堰塞坝坝料级配曲线,针对梯形、三角形和复式断面3种泄流槽断面型式,开展了堰塞坝漫顶溢流离心模型试验研究。分析不同除险断面型式对堰塞坝的泄流过程、总泄流量以及泄流后残留坝体几何尺寸的影响规律,并从水动力学的角度,对该泄流过程中泄流槽不同部位的水流特征进行了研究。试验结果表明,复式断面泄流槽不仅在初期泄流效率高、峰值流量小,而且残留坝体较低,总下泄水量最大,流量过程曲线具有"矮胖型"的特征,可迅速、最大程度的降低堰塞湖水位,同时能够有效的减轻因堰塞坝泄流给下游河道造成的防洪压力,是一种相对安全、高效的堰塞坝除险处置方法。     

Natural dam breaching due to overtopping: effects of initial soil moisture

Natural dams formed by landslides may produce disastrous floods after dam outbursts. How the breaching characteristics of natural dams are affected by initial soil moisture has remained insufficiently understood. In this paper, we present the results of a series of laboratory tests that assessed five different initial soil moistures (0.3, 2.4, 4.2, 7.3, and 10.3%). Under the present experimental conditions with dams composed of gravel–sand–clay mixtures, the failure of natural dams was primarily caused by the erosion of overtopping flow, and lateral mass collapse also caused breach widening. According to the test results, three stages of the breaching process of natural dams made of different initial soil moistures were observed. The results show that peak discharge increased with the increase in the initial soil moisture, while the breaching time and height of the residual dam decreased. In the process of the breach, the backward erosion was weakened gradually with the increase in the initial soil moisture. When the initial soil moisture increased, the breach deepened faster than it widened, and the ratio of the breaching width to depth after dam outburst tended to be greater than 1 at first and then less than 1. A function of the breaching width and depth is established, making it possible to calculate both variables. This function is based on a shape parameter that linearly decreases with initial soil moisture.

     

四川安县肖家桥堰塞湖稳定性初步评估

 四川省安县肖家桥堰塞湖是“5·12”汶川地震形成的高危堰塞湖之一,堰塞体高65～75 m,体积约250万m3,堰塞湖最大库容约2 000万m3。将三维激光扫描技术应用于堰塞湖地形测量中,迅速而准确获得堰塞坝的地形信息,为堰塞湖除险设计及稳定性评估提供重要依据。在现场利用三维激光雷达技术地形测绘和初步地质勘察的基础上,经过新旧地形图对比,指出有利于堰塞体稳定的结构性因素;通过经验与反演方法确定堰塞体的物理力学指标,经渗流计算与稳定分析,排除堰塞体坝坡失稳及管涌潜蚀两种溃决模式发生的可能性,指出肖家桥堰塞湖溃决模式可能以漫顶冲刷为主。     

尾矿库漫顶溃坝数学模型研究与应用

基于水砂混合物非平衡连续方程和动量方程,考虑尾矿库溃坝过程中溃口及底床变化对溃坝下泄物中尾矿砂体积浓度的影响,建立了一个描述尾矿库漫顶溃坝溃口发展过程和溃口下泄物流量过程的数学模型。应用该数学模型对某尾矿库漫顶溃坝过程进行了模拟,结果表明,尾矿库溃坝过程中下泄物体积浓度变化很大,前期下泄物以水为主,尾矿砂含量较低且以悬移质运动为主;后期下泄物主要以尾矿砂为主,水的含量很低,尾矿砂以推移质运动为主,当下泄物底床剪应力增量小于尾矿砂起动的临界剪应力时,溃坝过程停止。     

Modified risk assessment tool for embankment dams: case study of three dams in Turkey

Dam failures are catastrophic accidents resulting in property damage and loss of life. Risk prioritisation systems should be used in accordance with dam safety regulations to prevent these disasters. The purpose of this paper is to develop a risk assessment software which can be used by the decision makers for ranking of dams. Risk assessment was conducted on three embankment dams from Turkey to obtain information about the dam performance based on piping, earthquake, normal stability and flood failure modes. Parameters are incorporated into the programme to develop a new model that could predict variables such as breach width, dam failure time, side slope and peak breach discharge. The proposed tool gives flexibility to choose dam elements for describing the primary features of the evaluated dam; so users can make hazard categorisation of dams according to their risk level which is based on unique project conditions.     

Influence of reservoir water level variations on slope stability and evaluation of landslide tsunami

Reservoir filling and water level variations are important factors that induce slope failures near the reservoir banks. Once a landslide occurs, a tsunami might form which can result in a far greater disaster. This study provides insight and a method for analyzing the disaster chain of a landslide near the reservoir water by taking a slope near the bank of A’lagou reservoir in Xinjiang, China, as an example. The instability mechanisms of the slope are studied based on the field investigation and numerical analysis. The results show that there are two factors that increase the process of slope instability: the rock structure of the slope, which is an important internal factor, and the reservoir filling, especially the rapid drawdown which is an important external factor. Then, a numerical simulation that is based on SPH-DEM coupling method is used to evaluate the landslide tsunami process. The quantitative analysis of the tsunami indicates the initial wave height is about 22 m, the tsunami run-up on the opposite slope is about 44 m high, the maximum overtopping flow is about 1.35×10⁴ m³/s, the maximum velocity is about 9 m/s, the maximum overtopping depth is about 7 m, and the erosive velocity on the downstream slope of the dam is > 20m/s. The results of this study will be useful for preventing and mitigating landslide hazards in reservoirs.