常泰长江大桥主航道桥桥塔基础选型研究

Research on Pylon Foundation Types for Main Navigational Channel Bridge of Changtai Changjiang River Bridge

常泰长江大桥主航道桥为主跨1176 m公铁合建斜拉桥,桥塔基础采用沉井方案。为降低沉井自重和减少桥墩局部冲刷,采用理论分析、数值模拟与水槽冲刷试验相结合的方式对沉井基础型式进行研究。结果表明:在圆端形、梭形及矩形3种截面型式的沉井中,圆端形截面沉井的水流阻力系数最小;台阶型沉井相比传统沉井可以削弱墩前向下旋辊及减小墩侧高流速区的范围;台阶型沉井台阶宽9.0~10.0 m、台阶顶埋深位于0.6 H(H为沉井周边水深)处、挡墙高度为0.15 H时,可以起到较好的减冲刷防护效果。根据研究结果最终确定该桥采用圆端形截面台阶型沉井基础,其底面尺寸为95.0 m×57.8 m(横桥向×顺桥向),圆端半径28.9 m,台阶宽9.0 m,埋置在床面以下0.6 H处,台阶顶构造采用直角挡墙方案(挡墙高约4 m)。

The main navigational channel bridge of Changtai Changjiang River Bridge is a rail-cum-road cable-stayed bridge with a main span of 1176 m.Caisson Foundation was determined for the pylons.Theoretical analysis,numerical simulation and flume scour tests were conducted to figure out the proper type of caisson foundation that would have the minimum self-weight and be able to reduce the local scour of piers.The scour protection performance of the round-cornered,shuttle-shaped and rectangular caissons was analyzed and compared.The results show that the round-cornered caisson has the smallest water flow resistance coefficient,and the stepped caisson can mitigate the downward swirling and reduce the scope of pier-side high flow speed region,compared with the conventional type of caisson.It is shown that the stepped caisson exhibits good scour reduction and protection effect when the width of the step is set at 9 to 10 m,the top of the step is roughly parallel with 0.6 H(H refers to the depth of water around the caisson)and the retaining wall is 0.15 H in height.As per the research findings,the round-cornered caisson with step was finally chosen for the bridge,which measures 95.0 m(along bridge width)by 57.8 m(along bridge length)in base,with 28.9 m-radius round corners and a 9.0 m-wide step.The step is buried into the riverbed,at the location of 0.6 H.Right-angle retaining walls with height of about 4 m are added on the top of the step.