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。     

堰塞坝漫顶溃决过程数值模拟及应用

堰塞坝作为自然形成的天然坝体,其结构不稳定性强,绝大多数的堰塞坝最终都将发生漫顶溃决,一旦溃决,将会对下游带来巨大的生命和财产损失。因此,有必要合理预测堰塞坝的溃决流量过程,为溃坝应急预案的编制提供理论与技术支撑。本文充分考虑堰塞坝的形态特征及坝料的物理力学特性,建立了一个可合理模拟堰塞坝漫顶溃坝过程的数学模型。该模型可较好地反映水动力条件下的溃口发展过程和下泄流量过程。选择西藏易贡堰塞坝溃坝案例对模型进行验证,通过计算结果与实测资料的对比发现:计算得到的溃口峰值流量、最终溃口宽度、峰值流量到达时间等参数的最大相对误差均在±15%以内;溃口流量过程与实测资料也吻合较好,有效地验证了模型的合理性;参数敏感性分析结果显示,残留坝高、冲蚀模式(单侧与两侧冲蚀)、冲蚀系数等参数对溃坝过程均有重要影响。     

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。     

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。     

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。     

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。     

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。     

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。     

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。     

滑坡堰塞坝坝体溃决机理与溃决实验研究综述

相对于人工土石坝,天然形成的滑坡堰塞坝缺少加固、防渗及泄洪等工程措施来稳定堰塞湖水位,坝体结构不稳定、基础资料缺乏,发生的溃决现象具有突发性强、几率高、危险性大、排险处理紧迫的特点,亟需深入系统的研究.作者结合国内外堰塞坝形成及其溃决问题的研究现状,介绍了滑坡堰塞坝与人工土石坝的溃决特性、滑坡堰塞坝的溃决模式及寿命特征,以及滑坡堰塞坝溃决特性的物理模型试验研究、原型观测及大比尺现场试验研究、梯级滑坡堰塞坝溃决特性试验研究进展.最后提出了关于堰塞坝溃决机理、堰塞湖处置、溃决模式、原型及模型试验比尺效应、溃决过程原型监测预警等方面建议的研究方向.     

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。     

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.

     

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.     

土石坝管涌破坏溃口发展数值模型研究

由于坝体、坝基本身的缺陷或者穿坝建筑物的影响,渗透破坏是土石坝常见的一种破坏形式,管涌破坏在渗透破坏中占有很大比例。前人虽对土石坝管涌进行了大量的研究,但对管涌发生后的发展过程及其破坏规律还缺乏深入的研究。首先通过对可动颗粒受力情况的分析,推导出可动颗粒的临界水力梯度和管涌发展过程中土体孔隙率的变化,然后采用水流运动能量方程推导出管涌发展过程中管涌通道流量和流速的发展变化过程,得出了管涌通道流量的计算方法以及孔流转化为堰流的控制条件。在此基础上,提出了一个模拟土石坝管涌发展过程的数学模型,该模型可同时考虑土体的颗粒级配和密实度对管涌发展的影响,建立流量、流速与孔隙率的变化关系,确定管涌过程中的流量过程线,与目前国内外已有的模型相比,更为合理地考虑土石坝筑坝材料性质对溃口发展过程的影响。已有的大坝溃口实测流量过程线证实了该模型的合理性。     

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.     

粽粑水库对永川城区洪水影响及对策

永川城区萱花河上游粽粑水库,由于集雨面积扩大46.8%,使溢洪道溢洪能力不能满足要求,土质副坝将漫顶可能造成溃坝,严重影响下游城区人民生命及财产安全。论文提出了工程对策和非工程对策。