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Highway Bridge Collapsed in Shangluo, Shaanxi Province, China — 20 July 2024
Source: 澎湃新闻: https://www.thepaper.cn/newsDetail_forward_28204505
水利部水文首席预报员尹志杰接受央视采访时介绍，事发地位于社川河、金井河交汇之后的金钱河，在汇集点下游大概1公里的位置。金钱河属于典型的山区性河流，第一它有暴雨的集中区；第二洪水来得快、去得也快，水文上俗称叫“陡涨陡落”。
事发前，柞水县气象台7月19日14时52分发布过暴雨橙色预警信号，“预计包括杏坪镇在内的诸多地区未来3小时内降雨量将达60毫米以上，可能引发山洪、泥石流、中小河流洪水、城市内涝等次生灾害。
岩土专家陈志鹏观察新闻图片，指出塌陷部位中间下方的桥墩已完全看不到了。他根据事故发生后的照片推断桥梁结构的两种可能：一种可能是连续梁，即桥墩间距为20m，采用三点支撑，若是这种情况，能看出桥的设计已考虑了洪水问题，在中间做了加固；另一种可能是简支梁，采用两点支撑，由于中间桥墩坍塌，导致40m的桥面发生了"V型"破坏。
从图上看，桥梁一侧的挡土墙已经塌落。陈志鹏分析，“从岩土工程的角度来说，有可能这一部分的地质、地层条件不太好。挡土墙发生破坏，破坏材料冲击了桥墩。”
陈志鹏认为此桥在设计建造时已选择与河斜交（注：桥梁的纵轴线与其跨越的河流流向或路线轴向不相垂直），而非建在河流中间，布置是比较合理的。“在没有洪水的情况下，这段桥下基本水比较浅，大部分从河的内侧过去了。但遇到雨季山洪爆发，水位上涨、河面拓宽，可能洪水对桥墩的冲击力变大。”
长期从事道路桥梁施工、工程检测与监测工作的章辉推测，事故发生时，可能洪水冲刷基础，也可能夹带冲击物，使桥墩受损。
中国陕西商洛市高速公路桥梁因山洪局部倒塌。-照片：路透社/中国中央电视台
垮塌发生地点
7月20日，陕西商洛。图为柞水公路桥梁垮塌现场。中新社记者 张远 摄
垮塌发生地点
A portion of the bridge on Danning highway in China’s northwestern Shaanxi province lies submerged after collapsing on Friday night.
<aside> 💡 Here are what Yifan thought:
I conducted some preliminary research and also believe that it is unlikely that the bridge piers were damaged due to a landslide. I initially think the main cause lies in the design issues of the upstream highway bridge embankment, which severely weakened the left bank floodplain's flow capacity, directing all the floodwater towards the right convex bank. The destruction of the bridge piers and the landslide of the retaining wall should both be results of this flow condition, but there may not be a direct connection between the two.
Additionally, the damage to the bridge piers might have been caused by a combination of flash floods (including scour and flow-induced force) and debris impacts, which is similar to the Waiho River bridge collapse in New Zealand in 2019. However, due to the lack of hydrological, riverbed, and pier structure data, a comprehensive judgment cannot yet be made. It would be best to conduct some simple two-dimensional hydrodynamic simulations. I am still collecting further data, but I currently believe there are significant issues with the overall bridge layout.
</aside>
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