###### Abstract  
Groundwater is abundant in soft soil areas, which has a significant impact on the excavation deformation of foundation pits. In this paper, based on the monitoring of deep foundation pits with waterproof curtains in Shanghai deep foundation pits, COMSOL Multiphysics is used to model the layers of the foundation pits and establish a two-dimensional seepage-consolidation coupled model for hierarchical dewatering excavation. The feasibility of numerical simulation of regional foundation pits, the modeling method of the foundation pit seepage model is explored, and the presence or absence of waterproof curtains, and the influence of aquitards on the horizontal displacement of foundation pits and surface settlement outside the pits is analyzed. The research shows that the simulated foundation pit deformation values are in good agreement with the actual monitoring values and that the effect of dewatering and seepage has a great influence on the foundation pit deformation. The waterproof curtain has a significant effect on reducing the drop in the water level outside the pit and controlling the surface settlement. After installing a waterproof curtain, the amount of ground settlement is reduced, but the disadvantage is that the deformation of the enclosure structure increases. Finally, the influence of aquitard on the deformation of foundation pit excavation is simulated, and the distribution characteristics of the flow network diagram under different permeability coefficients are analyzed. According to the analysis of the foundation pit deformation law and flow network diagram, it is considered that the waterproof curtain can effectively reduce the influence of aquitard on foundation pit deformation.  
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Footnote †: journal: Applied sciences  
changes caused by the drop in groundwater level on the calculation of land subsidence and proposed a calculation method for ground subsidence outside the pit caused by dewatering in the foundation pit in the aquifer at different insertion depths of the waterproof curtain. [PERSON] et al. [10] conducted a finite element numerical simulation to analyze the deformation of the foundation pit and adjacent pipelines under the dewatering excavation of the foundation pit and studied the deformation response of the foundation pit and adjacent pipelines when the waterproof curtain was inserted at different depths under steady seepage. [PERSON] et al. [11] calculated the groundwater flow in three-dimensional conditions and soil deformation in one-dimensional conditions and analyzed the relationships among land subsidence, groundwater withdrawal volume, and groundwater level.  
In water-rich areas, the groundwater control system usually adopts the dewatering method of setting up pumping wells in the foundation pit to ensure construction safety [12; 13]. However, dewatering will cause groundwater to fall and retaining walls to move [14; 15], which, in combination, can lead to severe land subsidence. In the calculation of the horizontal displacement of the envelope structure, the effect of seepage is often ignored [16]. The effect of a waterproof curtain on the aquitard is rarely mentioned [17; 18]. Some scholars have simulated the seepage field of deep foundation pits and calculated the settlement during precipitation [19; 20; 21; 22; 23; 24; 25; 26; 27].  
This paper uses COMSOL Multiphysics to simulate the excavation process of the foundation pit, a deep foundation pit project in Shanghai. Compare the simulated data and the measured data, verify the accuracy of the fluid-solid coupling model, explore and analyze the role of the waterproof curtain in the deformation control of the foundation pit, and examine the influence of the permeability coefficient of the aquitard on the deformation of the foundation pit.