上海陆家嘴地区超深大基坑邻近地层变形的实测分析

结合上海国际金融中心超大体量卸载、超深开挖深度、超长降水周期的基坑工程实践,通过对邻近地层变形的信息化监测,研究上海陆家嘴地区超深大基坑在顺逆作同步交叉实施条件下邻近地层的时空位移特征,初步探讨其变形机理和影响因素。研究表明:重车动载对坑外地表沉降影响较大,地墙隆起对0.1H范围内的地表土体拖带上抬;地表沉降主要受软弱土开挖和承压井降水影响凹槽分布,纵向地表沉降空间效应明显,受顺逆作同步交叉实施影响差异沉降突出;坑外地层侧移角部效应明显,形成水平方向的土拱作用,并与系统刚度和土体硬度呈正比;坑内土体强隆起范围远超开挖面下1倍挖深,立柱隆起在第三和第五层土方开挖时发展速率明显较快;坑外设计挖深上部地层以斜向下位移为主,下部地层以斜向上位移为主;基坑土方开挖阶段,坑内地层卸荷隆起为主流动补偿为辅,坑外设计挖深以上地层土体流动补偿和承压井降水固结沉降均显著,而设计挖深以下地层以卸荷隆起为主兼有少量流动补偿。

Measurement and analysis of deformation of adjacent strata super deep and large foundation pits in Lujiazui District of Shanghai

Considering the building foundation pits of Shanghai International Financial Center with oversize unloading, ultra-deep excavation depth and super-long dewatering cycle of confined water and based on the informative monitoring of deformation of the adjacent strata for the super deep and large foundation pits, the time-space deformation features are studied for the super deep and large foundation pits by synchronous cross-excavation of the bottom-up and the top-down construction methods in Lujiazui District of Shanghai, and the mechanism and influencing factors are preliminarily discussed. It is shown that the surface ground settlement is obviously affected by the vehicle dynamical loads and the surface strata under the zone of 0.1H is uplifted by the rebound deformation of retaining walls. The distribution of the surface settlements seems to be grooved due to the excavation of soft soils and the dewatering of confined water. The spatial effects of the longitudinal settlements are uncommon and the differential deformation is prominently under the construction plan. The corner effect of the horizontal displacement in deep strata is strong, while the horizontal soil arch is formed and is proportional with the system stiffness and soil hardness. The influence zone of the powerful upheaval in the bottom can exceed a distance of about 1.0H from the excavation surface, where H is the final excavation depth, and the development rate of the column uplift is significantly faster at the third and fifth layers of soils at the excavation stage. The upper strata of the design excavation depth outside the wall are mainly oblique downward displacements, and the lower strata are mainly oblique upward ones. During the earth excavation, the upheaval in the bottom is mainly composed of unloading uplift and is ancillary by flow compensation of strata, and the upper strata of the design excavation depth outside the wall are significantly influenced by flow compensation of strata and consolidation settlement of the dewatering of confined water, while the lower strata are mainly caused by the upload rebound and a small amount of flow compensation.