Ground Deformation Associated with Deep Excavations in Beijing, China

Abstract

A performance study is considered to be reliable method for comprehending deformations associated with deep excavation. To gain insight into the laws governing ground deformations that are associated with deep excavation, details of 88 cases were collected and analyzed in Beijing. The results were compared with worldwide case histories. Field data were selected to survey the ground behavior and to examine the correlation between deformation and excavation. The position and magnitude of the final ground deformation (δv), as well as the maximum deformation (δvm), the correlations between δvm and excavation depth (H), the length–width ratio, embedded depth ratio (EDR), and the stiffness of the support system, were assessed. The clear evolution process, influence zone, and final deformation pattern are illustrated. Our study revealed the following: (1) the groove pattern is detected in the final deformation of the ground surface, δvm occurred when positioned approximately 0.42H~0.62H off the wall, when the 1st~2nd supports on the bottom were removed; (2) δvm increases with an increase in H, and it ranges from 0.04% to 0.12% when H has an average value of approximately 0.089%; (3) EDR has an observable effect on reducing the δvm, as there a slight impact was observed until the ratios exceeded 0.4; (4) the deformation value of the 75% monitoring points ranged from −25 mm to 0 mm; (5) excavation could cause minor upheaval in some areas, but the upheaval reduces with increasing levels of excavation, so both deformation magnitude and the number of points are low; (6) deformation exhibits clear temporal–spatial characteristics, the settlement rate gradually increased over time, especially after drainage started or consolidation appeared, and when the internal structure is completed, δvm decreases with the rise in support system stiffness, ranging from 7000 to 11,000, and deformation becomes stable; and (7) transverse sections near the excavation center experienced larger deformations than others and the smallest deformations were near the corners, a significant increase occurs with the removal of the lowest 1–2 struts, particularly on the long side where ∆δv reaches 2.8 ± 0.75 mm, and the influence zones extend from approximately 2.5H to 3H beyond the excavated face. These findings have valuable implications for designing and constructing similar projects in Beijing and other regions, as they can help prevent accidents and minimize resource wastage.