窗口坝调控粘性泥石流的拦淤机理研究

The window-frame dam is a new kind of opening dam type. The drain opening of the dam is larger than the slit dam and the horizontal-grid dam. Recently, the window-frame dam was widely used in China. However, the dam was seldom studied for current researches both at home and abroad. The trapping and back-silting mechanisms of window-frame dam for controlling viscous debris flow have not been revealed. Consequently, the fluid properties of debris flow and the working characteristics of the dam were not considered during the process of dam design. The theory evidence and the calculating method of related technical parameters are lacked for scientifically designing of the dam. . A large number of window-frame dams which were implemented in the Wenchuan Earthquake area are selected as research subjects in this proposed research program. The combined methods of field investigation, on-site observation, laboratory model experiment, numerical simulation and theoretical analysis are used for carrying out this research. Firstly, the trapping and back-silting processes and mechanisms of window-frame dam for controlling viscous debris flow are discussed and revealed. Then, the influence of the shape and size of the drain opening of the dam on the trapping and back-silting function is analyzed. Finally, the calculating methods for the key performance parameters reflecting the trapping and back-silting mechanism (including the change rate of density, peak discharge, velocity and grain composition; back-silting length and slope, etc.), and the key design parameters of the drain opening of the dam (including the critical block condition, height-width ratio, opening ratio, etc.) are established. The research results will provide theory basis and technical support for the design of debris dams.

窗口坝是一种坝体开孔尺寸大于切口坝和水平格栅坝的新型透过型拦砂坝，近年来，已在我国开始大量应用。目前，国内外对窗口坝的研究较少，其调控粘性泥石流的拦淤机理尚未揭示，造成在设计过程中没有考虑泥石流的流体性质以及坝体的运行特点，其科学设计尚缺乏理论依据和关键技术参数的计算方法。.本项目以汶川地震灾区大量已实施的窗口坝工程为研究对象，采用野外调查、定点观测、模型实验、数值模拟和理论分析的综合分析方法，探明窗口坝调控粘性泥石流拦砂节流、回淤缓坡的过程和机理。在此基础上，分析窗口坝窗口形状和尺寸对其拦淤性能的影响规律。最后，建立容重降低率、峰值流量削减率、颗粒级配变化率、流速降低率、回淤长度、回淤纵坡等反映拦淤机理的关键性能指标，以及窗口坝临界闭塞条件、高宽比、开孔率等窗口关键设计参数的计算方法，为泥石流拦砂坝设计提供理论依据和技术支撑。

针对目前广泛使用的窗口坝所面临的科学设计缺乏理论依据和技术参数指标，难以达到预期防治效果的问题，本项目采用野外调查、定点观测、室内模型实验以及数值模拟相结合的研究方法，开展了窗口坝调控粘性泥石流拦砂截流及回淤缓坡机理、窗口坝开口关键参数对拦淤性能影响及计算方法等研究工作。.本项目取得了如下重要结果：1）全面收集了汶川—北川两大泥石流重灾区已建窗口坝运行数据资料，对其工程防治效果进行了评价，并归纳总结了现有防治工程所面临的主要问题；2）开展窗口坝室内模型试验，建立泥石流容重降低率、峰值流量削减率、颗粒粒径变化率、流速降低率等关键拦砂截流性能指标的定量计算方法,并探讨了窗口坝拦淤性能与闭塞度之间的内在联系；3）总结了窗口坝库内泥石流淤积形态，将库内淤积形态分为四个区段：接触段淤积、稳定段淤积、过渡段淤积、残留段淤积；建立了库内泥石流的回淤坡度及相对淤高等回淤参数的定量计算公式，并分析推导了库内存在限制淤埋物情况下允许最大坝高的计算公式；4）研究了窗口坝的开口闭塞表现，建立了开口闭塞度的定量计算公式，提出了一种考虑窗口坝开口参数及泥石流容重的开口闭塞临界条件的综合判据F；以支持向量机和随机森林理论为基础建立了窗口坝闭塞度的SVM-RF判别方法，并总结了窗口坝防治效果评价与开口参数设计方法；5）基于数值模拟试验研究发现，窗口坝开口断面横向流速呈多峰形分布；泥石流纵向流速分布可分为：碰撞段、聚流段、消能段、自由段，并探究发现窗口坝对粘性泥石流的流量调控过程是窗口坝实体部分和开口部分共同作用的结果。.综上所述，本项目针对窗口坝拦淤机理及性能优化这一目标，开展了大量工作，并取得良好结果，对泥石流拦砂坝的设计和工程防治具有重要的现实意义。

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