跨度不等并行桥梁局部冲刷最不利桥墩位置研究

Study on Most Unfavorable Pier Position of Local Scour Around Parallel Bridges with Unequal Spans

为快速定位跨度不等并行桥梁的最不利桥墩位置,采用概化模型试验并结合数值模拟手段,探究了在不同桥梁跨径组合及桥孔布置方案下并行双柱式桥墩桥梁局部冲刷最不利桥墩位置的分布规律。结果表明:并行桥梁局部冲刷最不利桥墩位置沿河宽方向位于河道中心附近,沿流向则主要出现于两座并行桥梁各自第一排桥墩;局部冲刷最不利桥墩出现在哪座桥梁的具体位置取决于两座并行桥梁桥孔的相对布置方式,当下游桥桥墩位于上游桥桥墩的尾流区时,局部冲刷最不利桥墩位置位于上游桥,反之下游桥桥墩处于上游桥桥孔的束流区时,局部冲刷最不利桥墩位于下游桥;在实际工程中,提出几何变量θ值作为判别并行桥桥墩最不利冲刷位置分布的关键变量,该量反映出并行桥桥墩尾流区的影响范围,并由此指出局部冲刷最不利桥墩位置的判别方法,在沿流向和河宽方向定位最不利桥墩分布范围后,最不利位置可进一步用两座并行桥梁的桥墩连线与来流方向的夹角大小进行判断,当夹角小于14°时,局部冲刷最不利桥墩位于上游桥第一排墩,反之则位于下游桥第一排墩。研究结果可为跨度不等并行桥梁的抗洪设计、评估和防护提供参考和依据。

In order to quickly locate the most unfavorable pier position of parallel bridges,the generalized model test combined with numerical simulation method is used for studying the influence of span combination and arrangement of two-column abutment parallel bridges on the most unfavorable pier position.The result shows that the most unfavorable pier position of local scour around parallel bridges is mainly distributed near the river center along the river width and concentrates in the first row of piers of each two bridges along the flow direction.The most unfavorable pier position of local scour depends on the relative layout of two bridges’arches.When the downstream pier is within the tail flow area of upstream pier,the most unfavorable pier position is at the upstream bridge.Conversely,when the downstream pier is in the accelerated flow area,the position occurs at the downstream bridge.In practical engineering,the geometric variableθcan be used as a key variable in determining the distribution of the most unfavorable scour positions of parallel bridges,and it also reflects the extent of the influence of wake zone of parallel bridge piers,thus indicating the method of determining the location of the most unfavorable pier position.After locating the distribution of the most unfavorable piers along the direction of flow and the width of river,the angle between the first row of two bridge piers and the incoming flow direction could be expressed.When the angle is less than 14°,the most unfavorable pier is located at the first row of piers of upstream bridge,conversely,it is located at the first row of piers of downstream bridge.The study result can provide reference and basis for the design,assessment and protection against flooding of parallel bridges with unequal spans.