超深大截面沉井下沉及钢壳沉井应力监测研究

沪通长江大桥为公铁两用斜拉桥，其中29号主墩采用倒圆角的矩形沉井基础，结合现场施工，在钢壳沉井的不同截面上安装土压力盒和钢板应变计等监测元件，对沉井侧壁和隔墙不同位置的受力进行监测。结果表明:在大锅底开挖情况下，沉井受力类似深梁构件，两侧受压中间受拉，且中间隔墙的拉应力会随着沉井的不断接高而逐渐减小，最后变为压应力；沉井在施工中倾斜时，同一断面对称位置的受力有很大区别，且在沉井姿态稍有变化时，同一位置的受力也会发生突变，故应尽量保证沉井的姿态垂直；沉井在吸泥下沉过程中，会发生翻砂、突沉的情况，对沉井的受力会有很大的影响，这些影响可在钢板应变计的监测上有所体现。

On Monitoring of Ultra-deep Large-section Caisson Sinking and Stress in Steel Caisson

Hutong Bridge on Yangzte River is a rail-cum-road cable stayed bridge, wherein the No.29 main pier adopts, on round-off rectangular open caisson foundation. In the construction on site, earth pressure cells and steel strain gauges were fixed at different sections of steel caisson to monitor the stress at different positions on the side and partition wall of caisson. The result shows that, in the case of large span excavation, the force bearing status in the caisson is similar to that in deep beam component that the two sides are under pressure, the middle is in tension, and the tensile in the middle partition wall decreases gradually with continuous extension of caisson and, at last, becomes compressive stress; when the caisson inclines in the construction, the stresses at symmetric positions in the same section have great difference therebetween, and the stress at the same position may be subject to sudden change as the caisson attitude changes slightly, hence it is necessary for the caisson to try to keep it upright; during mud suction, sand boiling, sudden sinking may arise, making large influence on the stress condition thereof, and the influence will be reflected on the monitoring of steel strain gauge.