中文摘要：

国内外大量模型试验表明,＂陡坎＂式冲蚀是均质土坝漫顶溃决的重要机理。近年来,各国学者开发了一系列的考虑＂陡坎＂式冲蚀的溃坝过程数学模型,但模型均采用了＂陡坎＂出现在下游坡脚的假设。通过大比尺均质土坝漫顶溃决模型试验发现,对于坝高较大的均质土坝,＂陡坎＂出现的位置与漫顶水头和下游坝坡坡比存在内在联系,且＂陡坎＂的移动速率与坝料的物理力学指标相关,因此初始冲坑的位置和＂陡坎＂移动参数的选取对于溃坝过程模拟结果的合理性具有重要意义。本文借鉴国内外的漫顶溃坝过程数学模型,提出一个可考虑均质土坝漫顶溃决过程中＂陡坎＂移动的数学模型。该模型通过漫顶水流特征和坝体形状参数确定下游坡初始冲坑的位置,采用能量分析方法模拟＂陡坎＂移动,并通过室内与现场模型试验提出可考虑坝料黏粒含量、含水率、干密度等指标的＂陡坎＂移动参数;利用基于水流剪应力原理的冲蚀速率公式模拟溃口纵向下切与横向扩展;采用宽顶堰流量公式计算溃口流量,通过极限平衡法分析溃坝过程中溃口边坡的稳定性,采用迭代的数值计算方法模拟整个溃坝过程。选择国内外典型的大比尺均质土坝漫顶溃坝试验和有实测资料的溃坝案例对模型进行验证,并研究了是否考虑＂陡坎＂冲蚀对溃坝模拟结果的影响;通过模型计算分析可以得出,本文提出的数学模型可合理模拟均质土坝的漫顶溃坝过程。

英文摘要：

A large number of model tests show that headcut erosion is the major mechanism of homogeneous earthen dam breaching due to overtopping failure.In recent years,an array of mathematical models which can consider the headcut erosion are put forward,however,the initial headcut position is assumed at the dam toe downstream in these models.According to the large scale model tests of homogeneous earthen dam due to overtopping failure,for the dam with large height,the location which the initial headcut occurred is related to the water head of overtopping flow and the slope ratio of downstream,meanwhile,the velocity of headcut migration is connected to the physical and mechanical indexes of dam soil.It has great importance to choose the appropriate parameters to determine the initial scour position and headcut migration velocity.Based on the mathematical models of homogeneous earthen dam breaching due to overtopping failure at home and abroad,a mathematical model for homogeneous earthen dam breach process due to overtopping failure considering headcut migration is put forward.The model determines the initial scour position by means of the characteristics of overtopping flow and dam figuration parameters;it adopts a time-averaged headcut migration rate using an energy-based empirical formula,the headcut migration parameter which can consider the clay ratio,water content and dry density of dam soil is obtained through the indoor and field model tests;the vertical undercutting and horizontal expansion are simulated utilizing the erosion rate formula which is derived from shear stress principle of water flow.The model adopts broad-crested weir flow formula to calculate the breach discharge,in addition,limit equilibrium method is used to analyze the breach slope stability;the model adopts iterative calculation method to simulate the whole breaching process.The typical dam breaching cases of large scale model tests and actual dam which have measured data are chosen to verify the model,and the impact on the calculation results w