中文摘要：

由大面积大深度基坑开挖引起的土体卸荷回弹会对坑底桩基产生不利影响,这一影响对抗拔桩尤为突出。针对上海世博地下变电站的抗拔桩设计,采用基于非线性有限元的数值方法对抗拔桩在大面积深开挖过程中的受力特性进行了研究。首先通过对抗拔桩地面单桩静载荷试验结果的反分析确定土层本构参数,然后对抗拔桩在开挖过程和正常使用状态下的受力特性进行了数值分析。分析结果表明,基坑开挖引起的桩身轴力对抗拔桩的负面影响较轴心受压桩更为明显,在抗拔桩设计中应充分考虑开挖引起的预拉力,且扩底抗拔桩受到的预拉力大于等截面桩。正常使用状态下桩身轴力是土体回弹隆起引起的轴力和桩顶上拔的引起的轴力的叠加,应以此对桩身的钢筋配置进行校核。

英文摘要：

Soil unloading and rebound induced by large-scale deep excavation may affect the performance and integrity of existing piles inside the excavation zone, especially for up-lift piles. The non-linear finite element is employed to investigate the behavior of the up-lift piles in Shanghai Expo Underground Substation Project during deep excavation. Parameters of the subsoil are obtained by inverse analysis of the load tests on the up-lift piles. The behavior of the up-lift piles during deep excavation and under normal working load is analyzed by using the parameters. Results show that the tension force induced by excavation exerts a more negative influence on up-lift piles than normal piles. Therefore this pretension should be taken into consideration during pile design. Analysis shows the bottom-enlarged up-lift piles are subjected to a larger pretension force during excavation than ordinary up-lift piles. The pretension force of piles under working load can be deduced from the combination of the tension force induced by excavation and the tension force induced by working load.