均质土坝漫顶溃决过程研究

Based on dam height and dam material characteristics, experimental studies on the break of homogeneous earth dam due to overtopping failure will be performed by adjusting the centrifugal model test system for break of earth-rock dams which was developed by the applicant research team. Impact on the development rules of the breach and the hydrograph of break discharge during the break process due to dam shape, dam material characteristics and initial breach position will be focus on. Take advantage of the on time video monitoring system and the PIV image measurement system, the appear time of head cut, the critical height of the head cut, the movement velocity of the head cut, the transverse expansion velocity of the breach, the critical width of the breach and the collapse mode of the breach will be measured. Using the external flowmeter, the dam break duration and the hydrograph of break discharge will be measured. According to the similarity ratio, the development rules of the breach and the hydrograph of break discharge during the break process will be quantitative analyzed. Formula which can descript the development rules of the breach reasonably will be put forward according to the centrifugal model tests, appropriate erosion formula and discharge formula of break will be chosen, so as to modeling the numerical model for homogeneous earth dam due to overtopping failure. Calculation methods for the relevant numerical model will be put forward, computer software which can visually display the dam-break process will be also developed, and the rationality of the computer software will be validated by the dam-break cases and the test results. Based on the above results, theoretical foundation will be provided to improve the reliability for evaluating the disastrous consequences of homogeneous earth dams due to overtopping failure.

利用申请人团队研制的土石坝溃坝离心模型试验系统，针对我国均质土坝坝高、坝料性质等方面的特点，通过调节离心加速度，开展均质土坝漫顶溃决试验，研究坝体形状、坝料性质、初始溃口位置等因素对坝体溃口发展规律和溃口洪水流量过程的影响。利用系统的视频实时监测系统和PIV图像测量系统，量测"陡坎"出现时间、"陡坎"临界高度、"陡坎"移动速度、溃口横向扩展速度和临界宽度、溃口失稳坍塌模式，利用系统的外接流量计，量测溃坝历时与溃口流量过程线，结合离心模型试验相似比关系，定量分析溃口的发展规律和溃口流量过程。在此基础上提出能合理描述溃口发展规律的表达式，选择合适的冲蚀公式和溃口流量公式，建立均质土坝漫顶溃决过程数学模型，建议相应的数值计算方法，编制能直观显示其溃坝过程的计算机软件，并通过国内外典型均质土坝漫顶溃决案例资料和溃坝试验数据验证软件计算结果的合理性，为科学制定均质土坝漫顶溃决应急预案提供理论支撑。

据水利部大坝安全管理中心统计，自1954—2016年，我国有3534座水库大坝发生溃决，其中均质土坝占85%，而漫顶溃坝数占溃坝总数的50%以上。因此，有必要深入研究均质土坝漫顶溃决过程的溃决机理，揭示溃口形状和冲蚀形式的控制因素，提高均质土坝漫顶溃决溃口流量过程线的预测精度。通过本项目的研究，建立了国内外均质土坝漫顶溃坝案例数据库，通过统计回归分别构建了溃口峰值流量、溃口最终平均宽度和溃坝历时等相关参数的表达式，并与国内外常用的参数模型进行比较，验证模型的合理性和先进性；针对均质土坝漫顶溃决机理，采用土石坝溃坝离心模型试验系统，以坝高和黏粒含量为切入点，考虑坝体材料状态参量，从岩土力学的角度出发，结合水动力学理论和黏性泥沙输移理论，定量研究坝高、坝顶宽、下游坝坡坡比、初始溃口位置、坝料密实度、坝料含水率与坝体溃口发展规律、溃口流量过程之间的关系；基于均质土坝的漫顶溃决机理，建立能科学预测、精细模拟均质土坝漫顶溃决过程的数学模型，该模型基于坝体形状和漫顶水流特征确定下游坡冲蚀时的初始冲坑位置，采用基于能量法的冲蚀公式模拟坝轴线溃口处的坝料冲蚀，采用极限平衡法分析溃口边坡的稳定性，采用“陡坎”移动公式模拟溃坝水流的溯源冲刷，为了模拟实际溃坝情况，模型考虑了坝体的单侧冲蚀，两侧冲蚀及坝基的冲蚀，采用按时间步长迭代的数值计算方法模拟溃坝时的水土耦合过程，编制了相应的计算机软件；选择国内外具有实测资料的典型溃坝案例对模型进行验证，通比对峰值流量，溃口最终宽度及溃坝历时等参数发现，模型计算结果与实测值的相对误差可满足工程需求，验证了模型的合理性，并且通过与国外常用的均质土坝漫顶溃坝模型相比，本项目建立的模型可更为合理模拟均质土坝的漫顶溃坝过程。本项目的研究为提高均质土坝溃坝致灾后果预测精度，科学制定溃坝防洪应急预案，减轻因均质土坝溃决造成的损失提供新的有效手段。