澜沧江某巨型堆积体蓄水失稳诱发涌浪预测

Prediction of the wave induced by a gaint accumulation impoundment instability in Lantsang River

澜沧江上游拟建RM水电站,其蓄水运行可能导致近坝左岸RS巨型堆积体发生变形失稳,进而诱发滑坡涌浪灾害,威胁枢纽建筑物和下游居民安全。结合前期大量地质勘察及物理力学试验资料,采用大型离心机模型试验等方法,进行了RS堆积体蓄水潜在失稳破坏模式研究。在此基础上,建立了RS堆积体至大坝段全河道的三维数值模型,开展了RS堆积体滑坡-涌浪链式灾害动力学灾变全过程数值分析,对滑坡涌浪的首浪高度、对岸爬坡浪高、沿途传播特征、坝前浪高、沿大坝爬升高度等进行了预测分析。结果表明:随着水库蓄水位逐步抬升至2800 m高程,RS堆积体最可能发生较大规模的失稳破坏,其后缘拉裂边界为蓄水位以上一定范围的堆积体碎石土层、前缘剪切边界为堆积体中下部细颗粒层。堆积体失稳破坏后诱发滑坡涌浪,首浪高度在入水点附近达到峰值,约为31.5 m,历时约15 s。涌浪沿河道向下游传播通过①号河湾前后浪高衰减39.5%,涌浪在约147 s时传至大坝处并沿坝坡继续爬升,爬坡浪高约为2.6 m,历时180 s,首浪及后续小浪均无翻坝风险。首浪受大坝阻挡消能后,随即向上游反向传播形成回涌现象,回涌与后续涌浪撞击形成局部高浪区,至P5监测点处回涌浪高达到最大,约为4.56 m,历时219 s。涌浪传播过程中,河湾地形及回涌现象可大幅加速涌浪能量衰减,有效降低涌浪冲击与次生灾害风险。

[Objective]The RM hydropower station is proposed to be constructed in the upper reaches of the Lancang River.Its impoundment and operation might result in deformation and instability of the RS giant accumulation on the left bank near the dam,thereby triggering landslide-induced wave disasters and endangering the safety of the key hydraulic structures and the downstream residents.[Methods]This study combines extensive geological surveys and physical mechanics experiments to investigate the potential instability and failure modes of RS accumulation under reservoir filling.On this basis,a three-dimensional numerical model of the entire river channel from the RS accumlation to the dam section was established.An analysis of the dynamic evolution of landslide-wave chain disasters caused by RS accumulation was conducted,and parameters such as the initial wave height,wave height along the opposite bank,propagation characteristics,wave height at the dam front,and wave height climbing along the dam were predicted.[Results]The results indicate that as the reservoir water level is gradually elevated to an altitude of 2800 meters,the RS accumulation is most likely to undergo a large-scale instability failure.The rear tensile fracture boundary is the crushed stone and soil layer of the accumulation within a certain range above the reservoir water level,and the front shear boundary is the fine-grained layer in the middle and lower parts of the accumulation.After the instability failure of the accumulation,it induces a landslide-induced wave.The height of the first wave peaks near the water entry point,approximately 31.5 meters,and lasts for about 15 seconds.As the wave propagates downstream,the wave height decreases by 39.5%at the No.1 river bay,reaching the dam in approximately 147 s and continuing to climb along the dam slope.The climbing wave height is approximately 2.6 m and lasts for 180 s,with no risk of overtopping by the initial or subsequent smaller waves.After being impeded by the dam,the initial wave propagates upstream,creating a backflow phenomenon,which,combined with subsequent waves,forms a locally high wave area.At monitoring point P5,the maximum backflow wave height reaches approximately 4.56 m and lasts for 219 s.[Conclusion]During the wave propagation process,the topography of the river bay and backflow phenomena significantly accelerate the energy dissipation of the waves,effectively reducing the risk of wave impact and secondary disasters.