苏坡店沟“7·10”泥石流破坏都汶公路毛家湾大桥机理

摘要

The catastrophic debris flows on July 10 ,2013 resulted in huge destruction to Dujiangyan-Wenchuan highway(G213)in Sichuan Province of China. The highways were seriously destructed and blocked in 16 sites, which were induced by 7collapsed bridges and base,2 of 7 destructed were scoured by debris flow. Based on field investigation and analysis,the parameters were calculated,which were the density of 1. 88 g/cm3 ,the velocity of 9. 3 m/s,the peak flow of 232. 5 m3/s,and yield stress of debris flows1of 13. 3 kPa. The debris flows scoured the foundation of the bridge down the steep gully seriously,the pier lost its stability and the bridge collapsed. The cal-culation indicates that:the soil below the pier is scoured away by the debris flow leading to the pier overhanging, and the lateral length reaches 1. 65 m;on the other hand,the water in debris flows should run into the foundation soil,which reduces the soil’s strength. The pier failed when the maximum pressure(545 kPa)of the foundation ex-ceeding the allowable bearing capacity,then the bridge destroyed. By the analysis of the failure model and mecha-nism of Maojiawan Bridge,it suggests that debris flow drainage channel;clearance under the bridge and special protective projects should be carried out for highway protection and traffic security.%2013-07-10四川省汶川县岷江干流沿线群发性泥石流（简称“7·10”泥石流）对都（江堰）汶（川）公路（ G213线）和都汶高速桥梁、路基、隧道造成重大破坏，G213线和都汶高速共16处中断，尤以G213线破坏严重。苏坡店沟毛家湾大桥是“7·10”泥石流冲毁桥梁、造成交通中断的典型模式。在野外调查、采样和数据分析的基础上，确定苏坡店“7·10”泥石流的重度18.5 kN/m2，流速9.3 m/s，峰值流量232.5 m3/s，剪应力13.3 kPa。高速、大流量泥石流沿陡峻的主沟排泄过程中，强烈侵蚀和起动沟床，左侧桥基基础强烈淘蚀悬空，形成1.65 m宽的临空面；在泥石流的作用下，桥基沿主沟发生5m位移变形，导致桥梁垮塌，交通中断。经计算，桥墩下部土体支撑面积为42.8 m2，基底最大压力达545 kPa，大于规范规定允许承载力，并且从抗倾覆角度计算也超出了规范要求，处于失稳状态。针对跨越高陡泥石流沟的桥梁，建议加强泥石流沟排导、预设足够的桥下净空高度、增加桥梁防护等措施来减少桥梁的破坏。