逆作基坑开挖卸荷对工程结构的影响分析

以天津站交通枢纽深基坑工程为背景，基于开挖实测资料和数值模拟计算结果对比，对超深逆作基坑开挖卸荷引起的立柱桩隆沉、地下连续墙变形和层板变形进行了分析。结果表明，随着基坑的开挖，立柱桩与地连墙在竖直方向有一定隆起，中间柱的隆起量总体偏大；立柱桩间、立柱桩与地连墙间的差异变形随开挖的加深而持续增加，后者超过了设计控制预警值。地连墙水平位移沿深度呈近似的“弓形”曲线，坑口处有向坑外的侧移；水平位移最大值较顺作开挖小，出现的位置约为基坑开挖面以上1/2~1/3坑深处，与顺作法发生在基底开挖面附近有显著不同。水平层板竖向变形以隆起为主，最大竖向隆起出现在顶板中间区域的支撑柱附近。与此同时，文中还讨论了桩柱变形设计控制标准问题。

Analysis of influence of foundation pits excavation unloading by top-down method on engineering structures

Based on the deep foundation pit of Tianjin Transfer Junction Station, the settlements of diaphragm walls, deformations of upright post piles and plates due to excavation unloading of deep foundation pit by top-down method are analyzed through the contrast between measured data and numerical simulation results. The results show that the upright post piles and the diaphragm walls have some upheavals in the vertical direction; and the middle piles upheavals are bigger overall. The differential deformations of pile-pile and pile-wall increase with the increasing of the excavating depth, and the latter exceeds the warning value of design control. The horizontal deformation curves of the diaphragm walls are similar to "bow"; and there is lateral deformation towards the outside at the pithead. The maximum of the horizontal displacement is smaller than the normal construction method; and it occurs at about 1/3-1/2 of the pit depth away from the excavation surface. It is obviously different from the maximum at bottom of the excavation surface by normal construction method. Most of vertical deformations of horizontal plate are upheavals. The maximum of vertical displacement lies near the supporting column in the middle zone of top plate. Discussions on design control standards of the deformation of upright post pile are also made.