沪通长江大桥桥墩布设水动力特性试验研究

Experimental study on hydrodynamic characteristics of layout of piers of Shanghai-Nantong Yangtze River Bridge

沪通长江大桥横跨长江河口段的南通水道和天生港水道,该河段收径流和潮流共同作用,水流条件复杂。采用物理模型研究了工程河段水流特性,并重点分析了桥位断面流速、流向及单宽流量等。研究表明:桥位断面最大流速出现在南主墩所在的主槽附近,上游流量越大、下游潮汐越强,桥位断面处流速愈大;平常水文条件如98大洪水下条件下的水流不会对桥梁产生大的不利影响。但如果出现100a、300 a一遇极端水文条件,南主墩附近最大落潮、涨潮流速在3.7 m/s和1.3 m/s以上,在这种较强的双向水流作用,南主墩处会出现较大局部冲刷,同时施工时巨型钢围堰受到的水流作用远较桥墩要大,这对桥墩布设及其防护、施工围堰的设计和围堰安全提出了很高的要求。

Shanghai -Nantong Yangtze River Bridge goes across Nantong waterway and Tianshenggang water- way in the reach of Yangtze River Estuary. Under co-action of runoffs and tidal currents, this reach is of complex flow conditions. Its flow characteristics were investigated by using physical model tests, and the flow velocity, flow direction and discharge per unit width were analyzed. The study shows that the maximum flow velocity of cross sec- tion at bridge site appears near the main channel where the south main pier is located. The larger the upstream dis- charge is, the stronger the downstream tidal current is, and the flow velocity at the cross section increases. Under normal hydrological conditions like ＂98 flood＂, the flows will not have large negative effects on the bridge. However, under the extreme hydrological conditions with return period of a-hundred-year or 3-hundred-year and flow velocity of ebb tide above 3.7 m/s and rising tide of above 1.3 m/s near the south main pier, large local scour will occur around the south main pier under the action of such intense bidirectional flows. The effect on heavy steel cofferdam of the flows is more than the pier during simultaneous construction. Accordingly, higher requirements to the layout and protection of piers and the design of cofferdam construction and the safety of cofferdam are needed.