考虑坝后淤积的泥石流冲击拦挡坝动力响应研究

Dynamic Response Analysis for Debris Flow Dam with Sediments

“5·12”汶川强烈地震导致山体破碎,激发大量崩滑体堆积于坡面、沟道中,为震后泥石流的形成提供了巨量松散固体物源,使得泥石流起动临界雨量大幅降低,爆发频率急剧增加,成为震后主要的次生灾害类型。在多期泥石流作用下,拦挡工程会部分或全部淤满,从而逐渐失去减灾能力。然而,关于坝后淤积体对泥石流拦挡坝减灾效果影响仍缺乏定量研究。为此,基于弱可压缩光滑粒子流体动力方法(smoothed particle hydrodynamics,SPH),采用德鲁克−普拉格模型(Drucker−Prager,DP)准则及Herschel−Bulkley−Papanastasiou(HBP)流变模型模拟泥石流与坝后淤积体相互作用的动力过程。用该方法模拟了泥石流水槽物理模型试验,验证数值模拟方法的可靠性。在此基础上,进一步开展坝后淤积工况下红椿沟泥石流灾害的动力过程数值模拟研究。结果表明:在空库工况下泥石流过坝速度减小率为31.6%,半库工况下过坝速度减小率为16.4%,满库工况下过坝速度减小率为6.5%,坝后淤积使拦挡坝削峰效应降低,显著降低其拦挡效果;同时坝后淤积改变泥石流冲击拦挡坝动力响应过程,空库工况下泥石流表现出触坝、爬高、淤积等过程,满库工况表现为泥石流夹带淤积体过坝过程。半库工况坝体底部所受到的冲击力峰值相比空库工况减小13.25%,满库工况坝体顶部受到的冲击力峰值是空库工况的1.75倍。研究成果可为泥石流拦挡坝工程设计提供理论及技术支持。

The Wenchuan strong earthquake caused the mountain to break,and triggered a large number of landslides to accumulate in the slopes and channels.This provided a huge amount of loose solid sources for the formation of debris flows,which greatly reduced the threshold rainfall for the initiation of debris flows,and sharply increased the frequency of outbreaks,which became the main type of secondary disasters.Under the effect of multiple debris flows,the debris flow dam will be partially or completely filled-up,and the function of disaster mitigation has been reduced.However,there is inadequate research on the effects of sediment deposits behind the dam on the debris flow dam disaster reduction.In this study,based on the weakly compressible smooth particle flow(SPH),the Drucker−Prager(DP)criterion and the Herschel−Bulkley−Papanastasiou(HBP)rheological model are used to simulate the dynamic process of the interaction between the debris flow and the sediments behind the dam.The proposed method is verified by a flume experiment.On this basis,the model is further used to simulate the dynamic process of the Hongchungou debris flow disaster under sediments behind the dam.The research results show that the deceleration rate of debris flow through the dam is 31.6%under the condition of empty reservoir,the half storage conditions is 16.4%and 6.5%for full reservoir conditions.The sediments reduce the peak clipping effect of the dam,which significantly reduces the blocking effect.At the same time,the sediments behind the dam changes the dynamic response of the debris flow dam.Under the empty storage the debris flow shows the processes of dam hitting,climbing,and siltation,however the full storage shows the debris flow entrained by the siltation body passing the dam.In addition,the peak impact force at the bottom of the dam under the half-reservoir condition is reduced by 13.25%compared to the empty reservoir condition,and the peak impact force at the top of the dam under the full-reservoir condition is 1.75 times compared to the empty reservoir condition.The research results can provide a basis for debris flow dam design.