[14] conducted theoretical research on the stress and deformation characteristics of support systems based on linear elasticity theory. In constructing deep foundation pits in complex environments, the primary control conditions of foundation pit engineering have shifted from strength control to deformation control. The deformation of the foundation pit encompasses the surface settlement, horizontal and vertical displacements of the enclosure structure, and uplift of the bottom of the foundation pit. These deformations are influenced by the stress release, groundwater seepage, and soil rheology that occur after excavation of the foundation pit [15; 16]. Due to the coupling relationship between the displacement of the pit enclosure, the surface settlement, and the pit bottom uplift, conventional research methods are limited in reflecting the influence of multiple factors. Therefore, the analysis of pit deformation is mostly conducted through numerical simulation [17]. [PERSON] et al. [18] utilized the Midas GTS finite element software to establish a three-dimensional spatial model to simulate the excavation process of a deep foundation pit. The results indicated that the calculated values of pile deformation, pile top displacement, and axial force of internal support during construction were in agreement with the observed values. In a separate study, [PERSON] et al. [12] evaluated the impact of excavation in different sections of deep foundation pits on the deformation of adjacent subway tunnels using finite element models. The results indicated the accuracy of the finite element calculations. [PERSON] et al. [19] found, through numerical simulation, that considering the spatial effect during the excavation of ultra-long foundation pits can effectively reduce the deformation of the support structure and the surrounding strata. The numerical simulation method can better simulate the foundation pit excavation process under the premise of reasonable parameter selection. As such, it is important to conduct real-time construction monitoring of the foundation pit excavation process and obtain relevant parameters. [PERSON] and [PERSON]. [20] and [PERSON] and [PERSON] et al. [21] used software such as a self-developed three-dimensional finite element analysis program and FLAC3D to analyze the stress deformation characteristics of the support structure during the excavation process of foundation pits. Most prior studies have focused on foundation pits with straightforward geometries and single excavation events, and there is limited research on saturated soft soil in the Taizhou area near the ocean. However, the coastal areas in China are mainly saturated soft soil, which limits local engineering construction and development. Therefore, studying the excavation of foundation pits in saturated soft soil areas will be beneficial for proposing reasonable construction suggestions for the area, which can effectively alleviate the limitations of saturated soft soil on engineering construction. This study focuses on a geometrically complex deep foundation pit project located in Taizhou, China, characterized by its large span, irregular shape, and extremely deep muddy clay layer. Long-term in-situ monitoring and numerical simulation were implemented to study the deformation characteristics during the excavation of the deep foundation pit, and the horizontal and vertical displacements of the enclosure wall during the excavation of the pit, as well as its impact on surrounding buildings, were analyzed. The design of the foundation pit support structure was verified and evaluated, with the goal of offering guidance and recommendations for the design of comparable foundation pit support systems in deep foundation pit construction projects in Taizhou.