复杂承台群桩基础桥墩局部冲刷及冲坑形态研究

Study on local scour and scouring pit shape of complex cap pile group foundation

为研究水动力条件变化对复杂承台群桩基础桥墩局部冲刷的影响,以深圳市东宝河大桥主墩基础为研究对象,通过大比尺(1∶15)正态物理模型试验分析了桥墩基础在半掩埋条件下的局部冲刷坑形态、尺度及冲刷过程在不同水流偏向角度、水动力条件下的动力响应。结果表明:桥墩受小角度偏转水流的冲刷作用普遍增强;周边新建工程实施后,桥墩周围水深变小、流速变大,伴随着冲刷坑影响范围增大,水流偏向角为0°和5°时最大冲刷深度分别增加17%和16%;受复杂承台结构和群桩阻水效应的联合影响,沿桥墩轴线方向产生的3个冲刷坑尺度依次递减,至冲坑末端为沙脊淤积;冲刷坑在立面上呈现出从倒圆锥变化至半椭圆形态,且随着高程增加,冲刷坑水平方向尺寸增幅放缓而横截面面积显著增加。研究成果可为类似复杂桥墩型式的桥梁安全运行提供参考。

In order to study the influence of hydrodynamic conditions change on the local scour of bridge foundation of complex cap pile group,the main pier foundation of Dongbao River Bridge was taken as a research object.A large-scale(1∶15)normal physical model test was carried out to study the shape and scale of local scouring pit,and the dynamic response of scouring process under different flowing angles and hydrodynamic conditions.The results showed that the scouring effect of small deflected flow on piers was generally enhanced.After the implementation of the new projects around the bridge,the water depth around the pier became smaller,the flow velocity became larger,and the influence range of the scouring pit increased.When the flow deflection angle were 0°and 5°,the maximum scouring depth increased by 17%and 16%respectively.Under the combined influence of the complex cap structure and the water-blocking effect of the pile group,the scale of the three scouring pits generated along the axis of the pier decreased in turn,and the sand ridge was deposited at the end of the scouring pit.The scouring pit changed from inverted cone to semi-elliptical shape on the elevation,and with the increasing of elevation,the increase of the horizontal size of the scouring pit slowed down,while the cross-sectional area increased significantly.The research results can provide reference for the safe operation of bridges with similar complex pier types.