均质土坝漫顶溃决“陡坎”移动参数确定

Determination of headcut migration parameters for homogeneous earth dam due to overtopping failure

"陡坎"冲蚀是均质土坝漫顶溃决时的主要破坏模式,"陡坎"移动的速度与坝料的物理力学指标具有内在联系,而目前国外给出各类"陡坎"移动模型很少考虑这些联系,且参数选取方法误差较大。基于水流能量耗散原理的"陡坎"移动速度模型,考虑坝料的黏粒含量、含水率、干密度等因素,参考国内外具有实测"陡坎"移动速度资料的水槽模型试验成果,拟合出"陡坎"移动参数的表达式,并结合水槽模型试验不同坝料的特点,给出了拟合"陡坎"移动参数的上下包线。参考美国农业部农业研究中心开展的7组均质土坝漫顶溃决试验的"陡坎"移动速度实测资料,验证了建议参数的合理性,并与国外典型的"陡坎"移动参数模型计算结果进行比较,给出了参数取值的参考方法;对"陡坎"移动参数中涉及的黏粒含量、含水率、干密度等指标进行参数敏感性分析,分析研究3个指标对"陡坎"移动规律的影响,为均质土坝漫顶溃决模型"陡坎"运移参数的选取和进一步研究"陡坎"抗冲蚀能力内在机理提供参考依据。

Headcut erosion is a major failure mode of homogeneous earth dam due to overtopping failure,and the velocities of the headcut migration have an internal connection with the physico-mechanical indexes. However,current foreign models studying the headcut migration rarely consider this connection,and may yield a relatively large calculation error. In this paper,based on a model for the headcut migration velocities utilizing the energy dissipation principle,meanwhile,considering the clay ratio,water content,and dry density of the dam materials,the measured water channel model test results of the headcut migration velocities have been chosen to fit the formula of the headcut migration parameters. Owing to the large variation of the dam materials,the upper and lower envelopes of the parameters are also put forward in the study. 7 large scale model tests carried out by USDA-ARS which have the measured headcut migration velocity data are chosen as the representatives to testify the rationality of the suggested parameters. The typical foreign models for the headcut migration parameters are chosen as well to calculate the headcut migration velocities. Through analytical comparison,the advantage of the suggested model is presented,and the reference range of the parameters is given. In order to analyze the impacts of clay ratio,water content and dry density on the rule of the headcut migration,the sensitivity analyses of 3 indexes are carried out.Those model test results can provide the approaches for determining the headcut migration parameters of the homogeneous earth dams,and give a reference for further studies on the mechanism of anti-erosion capability of the headcut.