Observed performances and spatial effects of a set of 40 m ultra-deep rectangular excavations in Shanghai soft soils

The accelerating development of deep excavations in urban environment has garnered much attention on the excavation-induced deformations and environmental impacts. This paper presents a set of five ultra-deep rectangular excavations with the depth of 39.31–45.45 m in Shanghai soft soils. An extensive monitoring program was conducted to record excavation-induced deformation and influence on the surroundings. The spatial effect of rectangular excavations was further discussed. Based on the analyses of the observed performances of the excavations, the key findings are as follows: (1) The maximum lateral deflections of the diaphragm walls δ hmax were about 0.10–0.55 % of the excavation depths H e at the end of construction, and significant spatial and temporal effects in δ h were observed. (2) The maximum ground settlement, δ vmax , was generally within 0.65 % H e , appearing at the distance of around 0.5 H e outside the pits. (3) The spatial effect was more obvious in narrow excavations in this study. (4) Smaller normalized excavation scales led to smaller normalized wall deflections, emphasizing the confining effect of excavations’ geometry. The measured performances of the deepest rectangular excavations in Shanghai soft soil and observed spatial effects can serve as a valuable reference for the design and research of future ultra-deep excavations.