<p>Asymmetric foundation pits in coastal areas have unbalanced soil pressure, high groundwater levels, and periodic changes in the tide level. Understanding the deformation behaviors of these foundation pits is crucial for ensuring construction safety. The asymmetric foundation pit in the seawall rehabilitation project in Haining City, Zhejiang Province, was used as a case study. A typical cross-section of the pit was selected to test the hydraulic and mechanical soil properties in different layers and monitor the lateral deformation at different depths. Plaxis2D was utilized to establish a finite element model to investigate the foundation pit’s deformation behavior during excavation. The results showed that the simulated and measured lateral deformations were in good agreement, indicating the reliability of the numerical model. The seawall caused an asymmetric load on both sides of the pit, resulting in torsional deformation of the entire excavation area. Changes in tide levels had the largest impact on the pit’s deformation, especially regarding bottom heave. The lateral deformation of the enclosure piles, surface settlement, and bottom heave increased with the seawall height or tide level. The bottom heave was 15.57% higher than the critical value for a 5.4&#xa0;m seawall height and exceeded the critical values by 15.57%, 54.74%, and 65.69% at the mean tide level, design flood level, and high tide level. The findings can provide guidance for the design and construction of asymmetric foundation pits in coastal areas.</p>