河床预开挖下超大型沉井基础局部冲刷试验研究  

Experimental Study of Local Scour of Super-Large Caisson Foundation under Pre-excavation of Riverbed

作　　者：杨程生[1] 俞竹青 夏鹏飞[3] 高正荣[1] 高祥宇[1] YANG Cheng-sheng;YU Zhu-qing;XIA Peng-fei;GAO Zheng-rong;GAO Xiang-yu(Nanjing Hydraulic Research Institute,Nanjing 210024,China;Nanjing R & D Tech Group Co. ,Ltd. ,Nanjing 210024,China;Jiangsu Provincial Transportation Engineering Construction Bureau,Nanjing 210004,China)

机构地区：[1]南京水利科学研究院,江苏南京210024 [2]南京瑞迪建设科技有限公司,江苏南京210024 [3]江苏省交通工程建设局,江苏南京210004

出　　处：《桥梁建设》2022年第1期72-79,共8页Bridge Construction

基　　金：国家重点研发计划项目(2019YFB1600700);交通运输行业重点科技项目(2019-MS1-011)。

摘　　要：常泰长江大桥主航道桥为主跨1176 m公铁合建双塔双索面斜拉桥,桥塔墩采用超大圆端形截面台阶型沉井结构(下端平面尺寸95 m×57.8 m,高72 m,台阶宽9 m),沉井基础采用河床预开挖下沉施工方案。为确定河床预开挖宽度、深度及该方案实施后需采取的防护措施,采用水槽局部冲刷及防护模型试验,分析河床不同预开挖深度、宽度下的超大沉井基础局部冲刷特性以及抛石防护效果,并从减少沉井周边局部冲刷的角度提出了最优河床预开挖方案和抛石防护方案。结果表明:随河床开挖深度增加,沉井周边局部冲刷呈递减趋势;随河床开挖宽度增加,沉井周边局部冲刷呈递增趋势,增幅随流速增大呈先增加后减小趋势,流速越大开挖宽度的影响越小;开挖深度为0.6h(h为开挖前水深)、开挖宽度为(1.1~1.2)D(D为沉井迎水侧阻水宽度)最为合理;在河床预开挖的基础上对沉井周边进行抛石防护,防护方案实施便利、效果明显。现场监测结果表明:在2020年度大洪水作用下,沉井基础周边河床冲刷幅度较小,且与模型试验结果相符。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.The stay cables are fanned out in double cable planes.The piers of the two pylons are supported by the super-large stepped caisson foundation with round corners.The caisson is 72 m deep,the bottom of which measures 95 m×57.8 m,and the step is 9 m wide.The open caisson is sunk via the pre-excavation of riverbed.To determine the width and depth of riverbed excavation and the protection measures that should be undertaken after the implementation of the excavation scheme,flume tests of local scour and model tests to check the protection appurtenances were conducted to analyze the local scour characteristics and effects of riprap protection under varying excavation depths and widths of riverbed.To maximize the surrounding local scour of the caisson,the optimal riverbed excavation and riprap protection solutions were proposed.According to the tests,the surrounding local scour of the caisson shows sign of gradual mitigation as the excavation depth of the riverbed increases.While the increase of excavation width of the riverbed leads to the intensification of surrounding local scour,the increment first increases as the flow speed becomes bigger and then turns to decrease,and bigger flow speeds exert less consequence.The ideal excavation depth and width are 0.6h(h represents the water depth before excavation)and(1.1~1.2)D(D refers to the water resistant width of water-facing side of caisson),respectively.The riprap protection was carried out on the basis of the riverbed pre-excavation along the circumference of the caisson,and the protection scheme was carried out with ease and the protection effect was sound.The on-site monitoring results demonstrate that the surrounding riverbed scour of the caisson foundation is minimal,which complies with the model test results.

关 键 词：常泰长江大桥 斜拉桥 台阶型沉井 河床预开挖 抛石防护 局部冲刷 模型试验 

分 类 号：U448.27[建筑科学—桥梁与隧道工程] U443.131[交通运输工程—道路与铁道工程]