南京长江四桥北锚碇沉井监控方案及成果分析

Monitoring and analysis of north anchorage caisson of Fourth Nanjing Yangtze River Bridge

在南京长江四桥北锚碇沉井首次降排水下沉过程中,对沉井结构的应力应变、刃脚和隔墙底部土压力以及侧壁土压力进行了监控。通过有限元分析,确定了隔墙中间部位的受力最大截面为监控重点,并埋设了钢板计和钢筋计;在刃脚和隔墙底部以及沉井侧壁的凹槽和凸起部位选取测点安装了土压力计。监控结果表明,沉井受力情况与隔墙底部的土体支承情况密切相关,最不利工况出现在下沉初期形成较大支承跨度时;刃脚和隔墙反力则随着土体支承装况的不同而改变;沉井侧壁凹槽部位的土压力明显小于凸起部位,通过设置凹槽可以有效降低侧摩阻力。

Through the finite element analysis of the north anchorage caisson of the Fourth Nanjing Yangtze River Bridge,the section to control the safety of the caisson during dewatering sinking is determined,and the monitoring instruments are installed.The stress,strain,bearing reaction force and lateral earth pressure during dewatering sinking are acquired.The results show that the worst condition for the structural safety occurs at the beginning of dewatering sinking of the caisson with a large span caused by excavation.The bearing reaction forces of cutting edge and cross walls change with the variation of support conditions.The convex and concave of the caisson wall can reduce the side friction effectively.