土石坝管涌破坏溃口发展数值模型研究

Numerical study on break development due to piping failure for earth-rock dams

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。

The seepage failure is a common failure mode of earth-rock dams because of the influence of dam body defects or trans-dam structures, and the piping failure constitutes a large proportion. A series of studies on piping have been conducted, and the corresponding models have been put forward. However, no deep studies on the development process and the failure rules after piping have been carded out. In this paper, the critical hydraulic gradient of moveable grain and the change of void ratio during the piping development process are given. Moreover, the calculation methods for the discharge through piping passage and the control condition of the transition from orifice flows to weir ones are also derived. Based on the above results, a mathematical model of piping development is put forward, and the gradation and the density are both analyzed by use of it. The relationship among the discharge, velocity and porosity is established. Comparison between this model and other existing models shows that the present model gives more rational consideration of the influence of break development process on dam material characteristics. The actual discharge hydrograph tests on the dam break have confirmed the rationality of the model.