Shanghai center project excavation induced ground surface movements and deformations

Abstract

Empirical data on deep urban excavations can provide designers a significant reference basis for assessing potential deformations of the deep excavations and their impact on adjacent structures. The construction of the Shanghai Center involved excavations in excess of 33-m-deep using the top-down method at a site underlain by thick deposits of marine soft clay. A retaining system was achieved by 50-m-deep diaphragm walls with six levels of struts. During construction, a comprehensive instrumentation program lasting 14 months was conducted to monitor the behaviors of this deep circular excavation. The following main items related to ground surface movements and deformations were collected: (1) walls and circumferential soils lateral movements; (2) peripheral soil deflection in layers and ground settlements; and (3) pit basal heave. The results from the field instrumentation showed that deflections of the site were strictly controlled and had no large movements that might lead to damage to the stability of the foundation pit. The field performance of another 21cylindrical excavations in top-down method were collected to compare with this case through statistical analysis. In addition, numerical analyses were conducted to compare with the observed data. The extensively monitored data are characterized and analyzed in this paper.

Keywords

deep excavation / foundation pit / soft clay / top-down method / field observation / ground surface movements / ground deformations

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Acknowledgments

This paper is supported by National Natural Science Foundation of China (Grant No. 51768065). The field monitoring measurements used in this paper were made available to the writers through the efforts of many organizations and individuals involved with the construction and inspection of the foundation pit of the Shanghai Center project. Special thanks to SGIDI for facilitating access to field data. In addition, the writers would like to acknowledge the support of Ms. Yashuang Bai and Mr. Yuxia Ji for data compilation and figures processing. Any views and opinions expressed in this case study are those of the writers and do not necessarily represent the views of the organizations or other individuals responsible for the design and construction of this project.

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