The overtopping breaching experiment for pilot channel has been carried out using two significantly different kinds of sand specimens to give a supplement and perfection for the breaching experiment of barrier dam. The tests indicate that the breaching phenomenon has obvious difference between the two kinds of dam under the same condition. When the baffle is removed, the breaching process of dam made of fine particle is dominated by the strong down cutting erosion and breaks more easily. However, the breaching process of dam made of coarse particle is dominated by the weak headward erosion caused by seepage outflow. The headward erosion face gradually develops to upper side and only when it reaches to the pilot channel vicinity, the dam can break easily. The tests also found that the downstream slop of dams has obvious effect on the breaching process. The steeper the slope is, the more easily the dam break, the bigger the average broadening rate of the breach is. A conceptual physical dam breach model based on the de Vries erosion formula for the computation of the outflow hydrograph has been developed. Good adaptability is showed through the verification of the model by using the measured test data.%针对当前堰塞坝溃决试验粒径取值偏低和粒径相差不大的现状，采用两组粒径差别明显的砂样进行了堰塞坝垭口漫顶溃决试验。试验表明，同条件下粗、细两种颗粒坝体的溃决现象有着较明显的不同。垭口挡板提起后，细颗粒坝体以下切侵蚀为主，冲刷强度比较剧烈，坝体较容易发生溃决；而粗颗粒坝体则是以渗流出流形成的溯源冲刷为主，冲刷强度较低，溯源面逐渐向上发展，只有当其发展到垭口下端附近时坝体才有可能迅速发生溃决。试验还发现，下游坝坡对溃决过程的影响比较显著，坝坡越陡，坝体越易溃决，溃口的平均展宽速率也越大。此外以de Vries输沙率公式为基础建立了具有物理意义的概念性溃口出流计算模型，并采用试验实测数据对该模型进行了验证，结果表明该模型具有良好的适用性。
展开▼
