Deformation Characteristics and Stability of Shaft-Type Foundation Pit Excavation

A case study of the shaft-type underground parking garage of Harbin Provincial Party Committee Square is conducted to examine the deformation characteristics of shaft-type foundation pit excavation and the influence of pit-in-pit excavation on the overall stability of the foundation pit. First, the deformation monitoring scheme and results of the shaft-type foundation pit are reviewed. Second, the finite element software MIDAS/GTS is used to create a finite element calculation model for shaft-type foundation pit, and the accuracy of the calculation model is verified by comparing it with the monitoring results. On this basis, the evolution law of the annular arch effect in the construction process of shaft-type foundation pit is discussed, and influencing factors such as foundation pit diameter and supporting pile diameter are analyzed. Finally, the secondary excavation in the shaft pit is analyzed using the strength reduction method, and the influence of the platform width and pit depth on the pit stability is studied. The results are as follows: (1) The maximum measured horizontal displacement of the pile is 3.5 mm, and the maximum settlement is 11.6 mm. (2) The circular arch effect of the circular foundation pit can be expressed using the soil′s medium principal stress vector diagram. The soil range of the circular arch effect gradually expands as the excavation depth of the foundation pit is gradually increased. (3) When the excavation depth ratio of the inner and outer pits is 0.44, the influence of inner pit excavation on foundation pit stability should be considered.