考虑湖盆摩阻效应的川藏铁路冰碛堰塞湖地震涌浪及溃决风险分析

川藏铁路沿线存在着众多冰碛堰塞湖,且大部分位于高烈度地震区,堰塞湖溃决洪水成为对线路方案起控制作用的灾害类型,而地震涌浪是导致冰湖溃决的主要诱因之一。目前湖泊地震涌浪计算公式一般忽略湖盆的摩阻效应,对水深较浅且糙率大的冰碛堰塞湖而言,计算值偏小。鉴此,通过开展不同水深、不同地震峰值加速度、不同糙率的振动台造波模型实验,研究湖盆摩阻效应对地震涌浪的影响。根据实验结果,建立考虑摩阻效应的地震涌浪计算公式,并利用漫溢型溃决临界水文条件提出了冰湖溃决判据;最后以川藏铁路帕隆藏布流域为例进行应用说明,从而建立一种与选线原则方案确定阶段精度要求相匹配的冰碛堰塞湖地震涌浪溃决风险评估方法。本文公式考虑湖盆摩阻效应,适用于水深较浅的冰碛堰塞湖,尤其是在大震强震情况下,其计算结果偏安全。

Seismic Surge and Outburst Risk Analysis of Moraine-dammed Lakes with Frictional Effect of Lake Basin Considered of Sichuan-Tibet Railway

There are many moraine-dammed lakes along the Chengdu-Tibet railway, and most of them locate in high-intensity seismic areas. Dammed lake outburst flood has become a type of disaster of the controlling factor of the line scheme, and seismic surge is one of the main causes of glacial lake outburst. At present, the friction effect of the lake basin is generally ignored in the calculation formula of seismic surge, and the calculated value is relatively small for the moraine-dammed lakes with shallow water and high roughness. Shaking table wave-making experiments with different water depths, peak accelerations and roughness are carried out to study the influence of the friction effect of the lake basin on the seismic surge. Based on the experimental data, the calculation formula of seismic surge considering frictional effect is established, and the criterion of glacial lake outburst is put forward according to the critical hydrological conditions of overflow outburst. Finally, the method is illustrated by applying it in the ParlungZangbo Basin of Chengdu-Tibet railway, and a risk assessment method of seismic surge dam outburst in moraine-dammed lake is established, that matches the precision requirements of the determination stage of line selection principle. This formula, considering frictional effect of the lake basin, is suitable for moraine-dammed lakes with shallow water depth especially in the case of large and strong earthquakes, and the calculated results are relatively safe.