Performance of a top-down excavation in shanghai: case study and numerical exploration

A 24-m-deep top-down excavation surrounded by densely packed properties in Shanghai has been constructed and monitored recently. Based on the well-documented field data, this paper presents a case study of the project. Performances of the excavation are presented and evaluated by comparison with case histories worldwide. After that, a series of numerical analyses are carried out to decide a reliable method to consider joints in the diaphragm wall in three-dimensional (3D) simulations through calibration with the field data. On the basis of the verified model, several numerical explorations are then carried out to investigate the performances of different construction scenarios. Through the study, the following findings are obtained: (1) joints in the diaphragm wall should be carefully considered when simulating the excavation with 3D models; otherwise, the calculated displacements near the corners would be underestimated dramatically; (2) using weaker materials to represent the lower part of the diaphragm wall has negligible impact on the calculated displacements; (3) the elevated road near the excavation is influenced negligibly; when the road is heavily loaded, however, the road undergoes significant uneven settlements due to the excavation; (4) if two adjacent excavations were constructed simultaneously, the displacement field would become very unfavourable.