考虑端部形状影响的矩形桥墩局部冲刷试验研究

文章以宽度相同、长度不同的矩形桥墩为研究对象, 考虑矩形、圆端形、三角尖形 3 种典型端部形状, 在铺设 10 cm 等厚定级配沙的矩形长直水槽内进行不同流速下桥墩局部冲刷室内试验, 量测不同时刻桥墩周边测点流场、墩周冲刷坑深度等参数, 结合基本理论对桥梁基础局部冲刷进行研究。结果表明: 圆端形和三角尖形端部桥墩前下降水流和墩周马蹄形涡流强度较矩形端部小; 在相同条件下, 圆端形端部桥墩最大冲刷坑深度相对于矩形端部桥墩减小 34.9%, 而三角尖形端部桥墩最大冲刷坑深度相对于矩形端部桥墩减小 66.7%; 在保证矩形桥墩长宽比 $ L/B \geqslant 2 $ 的前提下, 当弗劳德数 $ Fr \leqslant 0.111 $ 时 L/B 越小, 墩周冲刷破坏程度越小, 而当 $ 0.148 \leqslant Fr \leqslant 0.185 $ 时则相反。根据河道不同流速合理选择墩型, 能够更好地预防冲刷破坏。试验结果可为桥墩局部冲刷设计提供参考。

This paper takes rectangular piers with the same width and different lengths as the research object, and takes into account the three typical end shapes of rectangle, round end and triangle tip, and conducts local scouring laboratory tests under different flow rates in a rectangular long straight channel laid with graded sand of equal thickness of 10 cm. The flow field of measuring points around the pier and the depth of scour pit around the pier at different times are measured. Combined with the basic theory, the local scour of bridge foundation is studied. The results show that as for round-ended pier and triangular tipped end pier, the descending flow in front of the pier and the intensity of the horseshoe eddy around the pier are smaller than those at the rectangular end pier. Under the same conditions, the maximum scour pit depth of the round-ended pier decreases by 34.9% compared with that of the rectangular end pier, while the maximum scour pit depth of the triangular tipped end pier decreases by 66.7% compared with that of the rectangular end pier. Under the premise of the aspect ratio of rectangular pier $ L/B \geqslant 2 $, the smaller L/B is when Froude number $ Fr \leqslant 0.111 $, the smaller the scour damage degree around the pier is, while the opposite is true when $ 0.148 \leqslant Fr \leqslant 0.185 $. The rational selection of pier end shape according to different river velocity can better prevent scour damage. The test results can provide reference for local scour design of pier.