北洺河大桥桥墩布设对河道防洪安全的影响

Effect of Pier Layout on Flood Control Safety of Beiming River Bridge

拟建北洺河大桥所处河段为大曲率弯道,且受地形条件限制,桥梁中心线呈大角度扇形布设。曲线桥梁与弯道水流交会,水流条件尤为复杂。为研究北洺河大桥斜穿弯道河流情况下桥墩布设对河道冲刷及防洪安全影响,设计制作了1:60正态物理模型,开展不同洪水重现期下曲线大桥斜穿弯道河流河工模型试验研究。试验结果表明:受桥墩布设交角及弯道水流的共同作用,原设计方案不同重现期洪水工况下均加剧了桥位处河道右岸的冲刷,最大冲刷深度3.54 m,威胁堤防安全;水流顶冲右岸产生壅水,最大壅水高0.48 m;桥墩布置对下游河道的影响范围264 m。适度调整7号桥墩与水流夹角,同时对右岸河床铺设宾格石笼,控制最大冲刷深度减小到1.68 m,有效改善了桥墩与堤防间的水流流态,优化方案保护了行洪安全。

Beiming river bridge is located on a bending river, and the central line of the bridge is fan-shaped with large angle due to the limitation of topographic conditions. The flow conditions of curved bridge intersect with the flow of the bend are particularly complex. To study the influence of piers on river scouring and flood control safety when Beiming river bridge intersecting curved river, a 1:60 normal physical model was constructed. A model experiment was carried out to study the oblique crossing of the bridge in different flood recurrence periods. The results show that under the joint effect of pier intersection and bend flow, the scouring of the riverbed at the bridge site is aggravated in different flood periods, and the maximum scouring depth is 3.54 m, which threatens the safety of the river levee. At the same time, the damming is generated by the flow heading to the right river levee, and the maximum backwater is 0.48 m. The result of topographic and analysis data show that the influence range of pier layout on the downstream channel is 264 m. When the maximum scouring depth is reduced to 1.68 m by laying square gabion at the bottom of the right bank riverbed and the angle between pier No.7 and flow current is adjusted, it can effectively improve the flow pattern between pier and river levee and reduce the scouring depth of the riverbed at the bottom of the right bank. The optimized scheme can protect the safety of bridge when flood flowing.