超大型沉井首次接高受力及变形规律初探

依托马鞍山长江大桥南锚碇沉井的首次接高，对其竖向沉降、隔墙墙底土压力和隔墙底板受力情况进行了监测。结果表明，超大型沉井兼有条形基础的特点和整体工作性能，能够承受较大的竖向变形，与单纯考虑地基承载力相比，更适合于按变形控制接高。沉井接高时普通隔墙下的土压力小于分区隔墙，并且普通隔墙下部土体会先达极限承载力，后续接高产生的荷载转而由分区隔墙（或井壁）来承担。沉井首节混凝土浇筑就已决定了隔墙底板的应力大小和分布情况，后续接高不会再引起大的改变；隔墙底板中间部分受力较小，外围拉应力较大，通过井壁外土体的密实回填可有效降低此部分拉应力。

Research on stress and settlement of super-large open caisson during first lifts

During the construction of south anchorage open caisson of Ma’anshan Yangtze-River Bridge,the settlement of the open caisson,the earth pressure under the cross wall,the stress of the bottom steel plate of cross wall were monitored.It is found that the super-large open caisson has the characteristics of both strip footing and block foundation.As large settlement is acceptable for the first lifts,the open caisson settlement control method is more suitable than the soil bearing capacity control method.The earth pressure under the common cross wall is smaller than the division cross wall;and the ultimate bearing capacity of soil under the common cross wall is also smaller.When the limit equilibrium state for soil under the common cross wall is reached,the load added during the following lifts is taken by the division cross wall(or the side wall).The stress in the bottom steel plate of cross wall is determined mainly by the concrete pouring of the very first lift,and it is less affected by other following lifts.The stress of the bottom steel plate of cross wall is smaller at the inner part,and bigger at the outer part.The tensile stress near the open caisson side wall can be reduced remarkably by sound compaction of soil backfilled outside.