特大型地下结构施工差异变形控制

Controlling on differential deformation during the construction of super huge underground structure

差异变形是逆作法施工中最关键的问题,如果立柱桩之间或与地下连续墙之间差异变形超过允许值,结构的安全将受到影响。地基刚度系数法是分析地下结构差异沉降的有效方法。以上海世博500kV全地下变电站工程为例,采取数值方法研究特大型深基坑开挖前后立柱桩极限承载力和竖向支承刚度变化,结果表明:因上覆土体的移去和坑底土体回弹作用,开挖后立柱桩的极限承载力和竖向支承刚度显著降低;分析地下结构的差异变形时,应对基坑开挖前的静载荷试验结果进行修正,并对立柱桩和地下连续墙的竖向刚度系数予以折减;上海世博500kV全地下变电站工程的立柱桩、地下连续墙和地下结构设计满足差异沉降要求。

Differential deformation is a key problem in reverse construction.The structure will not safe when the differential deformation is beyond the limit between the post piles or between piles and diaphragm walls.The ground stiffness coefficient method is effective in analyzing the differential deformation of structures.Taking an example of Shanghai world Expo 500kV underground substation project,the ultimate capacity and vertical rigidity of post piles before and after excavation was studied with numerical method.The results show that the capacity and rigidity of post pile after excavation obviously reduced,due to unloading of deep foundation pit excavation and rebounding.The static loading test results should be modified and the vertical bearing stiffness coefficient of post piles and diaphragm walls which is used for analyzing the differential deformation should be improved.The differential deformation between the post piles or between piles and diaphragm walls in the substation engineering can satisfy the deformation limitations.