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.