基于物理模拟的堰塞湖溢流溃决机理

Barrier Lake Break Mechanism with Physical Model

受持续来流影响,在大江大河内形成的堰塞湖极易在数十天甚至数天内漫顶溢流溃决,引发非常态溃决洪水,严重威胁下游沿岸地区人民群众生命财产安全。堰塞湖溃口坍塌变形发展迅速、现场观测难度大,当前普遍难以实地观测堰塞湖溃口形态变化及水力学参数,至今未能获取溃口坍塌发展的真实数据。针对堰塞湖溃决洪水威胁及溃决机理不明等难题,基于堰塞湖溃决过程现场观察及历史堰塞湖溃决案例分析,阐明堰塞体体型、材料级配、库容及上游来水量是决定堰塞体危险性的关键。并以“11·3”白格堰塞湖为原型,分别开展了堰塞湖溃决1∶80室内和1∶20野外物理模型试验,揭示堰塞体溃口发展遵循“流速驱动、流量控制”,以获得较大流速为目标的自我演化机制;溃口坍塌发展的主要动力机制是携沙水流剪切冲刷、陡坎上游负压区涡流掏刷、陡坎下游高速水流冲刷、边坡重力坍塌;堰塞体溃决坍塌依次呈现尾部下切、陡坎溯源、全断面下切、上冲下淤4个发展阶段变化特征,溃口平面形态相应依次呈现线条型、倒喇叭型、双曲面型、近似等宽型4个变化特征。陡坎溯源是溃决前最高效的冲刷方式,也是判断堰塞体漫顶过流后是否溃决的重要标志。开展堰塞湖溢流溃决大型物理模拟试验有助于推动高危堰塞湖应急疏通排水设计和堰塞体坍塌控溃技术发展,为堰塞湖应急处置提供参考。

In view of the continuous incoming flow, barrier lakes in the large rivers are quite easy to be overtopped within dozens of days or even just several days and result in an extraordinary flood, seriously threatening the lives and property of people on both sides. Due to the rapid collapse deformation of the barrier body and high observation difficulty, it’s quite hard to accurately observe the breach morphology changes and hydraulic parameters at the emergency disposal site, thus obtaining no real data on the breach morphology development so far. Aimed at the huge outburst flow peak threat and ambiguous outburst mechanism, the historical barrier lake cases were investigated and revealed that it was the barrier body shape, particle gradation, reservoir capacity, and the incoming flow that determined the danger degree of the barrier lake. Moreover, referring to the Baige Barrier Lake, the large scaled 1∶80 indoor and 1∶20 outdoor physical models were both carried out to find out the breach morphology, which followed the principle of outburst flow velocity drive and outburst flow rate control. The main dynamic mechanisms of the breach development were the shear scour of sand-carrying flow, the vortex scours at the retrospective step, longitudinal scour by the high-speed outburst flow, and lateral slope collapse by gravity. The whole breach development process could be successively divided into four stages: Tail downcutting, retrospectively scouring, full section downcutting, and upstream scouring and downstream silting. Correspondingly, the horizontal breach morphology successively presented the four features of linear, inverted trumpet, hyperboloid, and approximately equal width. The retrospective step was the most efficient and determines whether the barrier body would break down. The large-scale physical model can promote the development of emergency drainage design and barrier body outburst control, providing a reference for the emergency disposal of the high-risk barrier lake.