上海中心大厦裙房深大基坑工程围护墙变形分析

 上海中心大厦的深大基坑工程采用主楼顺作、裙房逆作的总体施工方案。针对裙房基坑四周中间部位的围护墙变形特点，采用简化的二维计算模型，结合实测数据对其进行分析；讨论主楼区与裙房区之间的临时隔断圆形地墙的简化方式和是否考虑地下水的作用对计算结果的影响，并分析基坑开挖宽度及临近基坑北侧的金茂大厦地墙对基坑变形的影响。结果表明：在不考虑圆形地墙受偏载作用时，计算中可将圆形地墙按水平位移约束简化处理；土体采用修正剑桥黏土本构模型，土体计算参数宜采用有效应力指标，并同时考虑地下水位的作用；墙体变形随基坑开挖宽度增大而增大，但最终趋于收敛。测点的变形计算值与实测值结果比较吻合，而在施工场地进出口位置和两地墙距离很近位置(图1的测点P04)的实测值和计算值相差较大；分析表明，车辆动载及圆形地墙在偏载作用下的抗侧刚度弱化明显增大围护墙体变形；而临近基坑外侧金茂大厦的地墙存在，却在一定程度上减小墙体变形。

ANALYSIS OF RETAINING WALL DEFORMATION FOR DEEP AND BIG FOUNDATION PITS OF PODIUM IN SHANGHAI TOWER

The main building of Shanghai Tower is constructed by bottom-up construction method,and the podium pit uses top-down method.The wall deformation of the podium pit in the middle part of edges is analyzed with simplified 2D numerical models and measured values.The effects of simplified methods for the circular wall,which is a temporary partition between the main building and the podium construction areas,and whether to consider the effect of groundwater on calculation results are analyzed.The effects of excavation widths and the diaphragm wall of Jinmao Building(JMB) on the wall deformation are also discussed.Analysis results show that in condition of without considering the effect of eccentric load on the circular wall,the boundary for the circular wall can be simplified to rollers.When the modified Cambridge clay(MCC) model is used to simulate soils,the mechanical parameters of soils should adopt the effective stress indices,and the effect of groundwater should be considered at same time.And the wall deformation increases with the increases of excavation width,but eventually converges.The results of calculation agree with field measurements at normal positions,but have a large difference with observed data at the positions,which are the entrances at the construction site and the position(P04 in Fig1) that the distance between two walls is very small.The results show that the vehicle dynamic load and the lateral stiffness weakening of circular wall significantly increase the wall deformation,and the JMB diaphragm wall adjacent to the pit reduces the wall deformation to some extent.