## 1 Introduction  
With the accelerated development of urbanization in China, the concentration of population in cities has brought many challenges to the construction of infrastructure. Not only is the space above ground utilized for new facilities, but also sufficient attention has been paid to the development of urban underground space. Therefore, numerous underground constructions, such as subway stations and underground shopping malls, emerge during the expansion of urban areas. Meanwhile, the volume of single buildings continues to increase, and the structures become more complex; thus, the construction of large-scale and multiple-blocked foundation pits are more common [1; 2; 3; 4; 5; 6]. The design and construction of an excavation group is becoming increasingly common in engineering practices. Compared with the excavation of a single foundation pit, a foundation pit group would experience larger earth pressure unloading, larger superposition of earth pressure and deformation, and a longer construction period. In addition, more significant temporal and spatial effects on a foundation pit group would give rise to excessive deformation and greater construction risks. Therefore, extensive studies and research have been performed to provide insight into the deformation of foundation pits and the surrounding facilities by many scholars [7; 8; 9; 10; 11; 12; 13; 14]. [PERSON] et al. [15] observed the deformation characteristics of an 18.4 m deep triangular foundation pit in Shanghai soft clays using a monitoring system. [PERSON] and [PERSON] [16] proposed a new theoretical approach to evaluating ground deformation and wall deflection at any section within the influence zone of a braced excavation. Based on the finite element method, [PERSON] and [PERSON] [17] analyzed the stress state of soils in the process of deep excavation. [PERSON] [18] studied the active earth pressure and lateral wall deflectionsin a deep excavation group via theoretical and numerical analyses. The effect of soil width on the transition of lateral earth pressure was investigated. [PERSON] [19] proposed the superposition mechanism of the environmental impact of a single excavation and investigated the environmental deformation, such as the lateral deformation of the retaining structure, the ground settlement, and the deformation of nearby buildings and pipes, induced by the excavation group. [PERSON] et al. [20] proposed the divided alternate excavation method (DAEM) to mitigate the influence of a newly excavated underground construction on existing tunnels and the feasibility and advantages of DAEM in limiting the deformation of tunnels were well demonstrated by field measurements. [PERSON] et al. [21] introduced the concept of a deep excavation group and systematically studied its characteristics through several project examples, which gave insight into key scientific problems regarding deep excavation groups. [PERSON] et al. [22] investigated synchronous excavations in Shanghai soft soils and analyzed the effect of the buffer width of synchronous excavations by numerical simulation based on a practical project. An excavation group composed of four foundation pits in Shanghai was investigated in this paper to analyze the interaction between adjacent pits and the complex deformation mechanism. The whole excavation project covered an area of 38,744 m\({}^{2}\) and was excavated to 10.6 m below the ground surface. To ensure the safety of the foundation pit group, the overall construction principle of the project was that the main structure can be constructed at the same time, but the foundation pit should not be excavated until the underground structure of the adjacent foundation pit is finished. Thus, the space-time effect of the foundation pit group was obvious due to the large total area, the large excavation depth, the long construction period, the multiple unloading, and the superimposed influences of the foundation pits.