摘要
溃坝问题的研究可分为两大方面的内容。一方面是溃坝洪水波在坝下游河道传播演进过程问题,另一方面是大坝自身破坏溃决过程问题。本文研究的为后一方面的内容。造成大坝溃决的原因很多,如超标洪水引起水库漫顶、坝身渗透破坏和坝身滑坡等,不同原因引起的大坝破坏溃决过程也是不相同的。本文研究的为均质土坝因超标洪水引起水库漫顶后,坝身在漫顶水流作用下冲刷、破坏和溃决全过程的模拟,以及为进行这个全过程模拟所需的一些基础问题的研究。
本文首先建立了坡面水流运动的一维和二维数学模型,为溃坝水流计算提供了一种新的计算方法。在此基础上建立了陡坎形成和发展数学模型,坝体冲刷采用试验得出的起动切应力和冲刷率计算式计算。陡坎坍塌模式和横向坍塌模式的建立为均质土坝漫顶后冲刷破坏过程中溃口形成和发展模拟提供理论基础,考虑了地形随机起伏变化和抗冲性能差异两个影响因素单独和综合作用对均质土坝漫顶溃决过程的影响。全文主要讨论了以下几个方面的问题:
(1)叙述了均质土坝漫顶后冲刷破坏过程模拟的研究目的和意义,综述了土体起动冲刷、土坝漫顶溃决模拟和冲沟网形成研究现状,拟定了本文的主要研究内容。
(2)推导出坡面坐标系下水流运动一维和二维数学方程组,再通过坐标变换转换成水平坐标系下的方程组,该方程组适合计算坡度较大的坡面水流运动,对方程进行离散并进行程序编制。选取三种不同坡度的坡面进行洪水演进计算,分析比较方程有无修正以及坡度变化对水流计算结果的影响。
(3)建立了均质土坝漫顶溃决过程一维数学模型,模拟了陡坎的形成和发展过程。土坝在漫顶破坏过程中逐渐发展成为陡坎,陡坎的坍塌将引起坝顶高程大幅降低并形成溃口。在模型中通过力学平衡原理建立了陡坎坍塌模式,滑动面不局限于通过坡脚点。通过计算分析比较了有无陡坎坍塌对土坝漫顶溃决的影响。坝体冲刷采用多种土样在矩形管道水槽中进行试验,根据试验结果分析土体起动切应力和冲刷率分别与各自的影响因素之间的对应关系,推导了起动切应力和冲刷率计算式。
(4)在推导出的坡面二维水流数学方程基础上建立了均质土坝漫顶溃决过程二维数学模型,在模型中根据力学平衡原理建立了土体横向坍塌模式,纵向坍塌采用陡坎坍塌模式。模型中引入筑坝土体起动切应力和冲刷率计算式计算坡面土体的冲刷。通过计算分析了地形起伏变化和抗冲性能差异两个因素单独和综合作用对均质土坝漫顶溃决过程的影响,并应用建立的模型对含导流渠土坝溃口刷深及展宽过程进行了模拟。
The research on dam-break problem can be divided into two aspects. On the one hand is the process of transmition and evolution when the dam-break flood wave is in downstream riverway, on the other hand is the process of the dam own breaking and bursting. In this paper, we put an emphasis on the latter one. Dam bursting caused by many causes such as reservoir overtopping caused by excessive flooding, infiltration and damage of dam body, landslide of dam body, and so on. The process of the dam bursting is not the same according to the factors which causes the damage. In this paper, simulation of the whole process in which the homogeneous earth dam body is eroded, destroyed and finally burst by the power of the overtopping current when the reservoir is overtopped due to the excessive flooding is projected, and some studies of the basic issues which are needed in the simulation is also paid attention to.
The one dimension and two dimension mathematical model for the current movement on slope is established firstly, which provide a new method of calculation for the flow of the broken dam. On the basis, the mathematical models of scarp formation and development are established. The formula for starting shear stress and erosion rates which is educed by the examinnation is adopted to calculate the erosion of the dam. The establishment of scarp collapse mode and lateral collapse mode provide a theoretical basis for the simulation of the bursting breach formation and evolution in the process of eroding and destroying when the homogeneous earth dam is overtopped, considering the effects caused by the terrain random undulation and the the impact resistance property diffence which affect separately and synchronously on the dam overtopping. The paper mainly discussed the following issues:
(1) The research purpose and significance of the simulation to the process of the homogeneous earth dam overtopping erosion and damage is described, the research status quo on the soil starting, erosion, dam breaking simulation and gullies network formation is reviewed, the main contents of this article is drawn up.
(2) One and two dimensional water movement mathematical equations are deduced under the slope coordinate system, and the equations are transformed to the equations under the plane coordinate system. The equations are suitable for calculating the water movement under the condition of the large slope, equations are dispersed for programming. Three different slopes are selected for flood calculation, and the results of flow are analyzed and compared with or without equations amendment and the change of slope.
(3) One dimensional mathematical model of the process of earth dam overtopping and break is established to simulate the formation and development process of the scarp. Earth dam gradually develops into the scarp during the process of overtopping and break, the collapse of scarp will lead to dramatically reduced crest elevation and the formation of dam breach. The scarp collapse mode is established in this model through mechanical equilibrium, and the sliding surface is not limited by the foot of slope. The effects of existence and nonexistence of scarp collapse on the earth dam overtopping and break are analyzed by means of calculation. A variety of soil samples are put in a rectangular pipe flume to experiment in the dam erosion trial. The corresponding relationship of incipient shear stress, erosion rate and their influencing factors is analyzed according to the experiment results, two formula of incipient shear stress and erosion rate are presented.
(4) The two dimensional mathematical model of the process of earth dam overtopping and break based on two dimensional flow mathematical equations on the slope is established. Transverse collapse mode of the soil body is established in this model according to mechanical equilibrium, and the scarp collapse mode is adopted in longitudinal collapse. The formula of dam soil starting shear stress and erosion rate is adopted to calculate the erosion of the slope soil in the model. The effects caused by the terrain random undulation and the the impact resistance property diffence which affect separately and synchronously on the dam overtopping is analyzed by means of calculation, and the simulation of the deepening and widening process of earth dam crevasse with one and two diversion channels is processed by using the established model.
引文
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