The dual-purpose diaphragm wall, serving as both a temporary retaining structure and the permanent exterior wall of underground structures, has been extensively used for deep excavations in soft soil areas. Within some cases, soil mix panels are installed on both sides to enhance ground deformation suppression during excavation. Further research is essential to assess the effectiveness of this type of retaining structure in mitigating ground deformation caused by excavation in specialized soft soil areas. This paper utilized monitoring data to present a case study on the deformation characteristics of a 20.6-m-deep excavation supported by diaphragm walls supplemented by soil mix panels in soft soils, detailing its impact on adjacent pipelines and buildings. The findings revealed significant creep deformation properties of the surrounding ground. The diaphragm walls can effectively confine deformations caused by deep excavations to a limited extent. When supplemented with soil mix panels, greater deformation control efficacy can be achieved. Notably, the combined diaphragm and soil mix wall system exhibits maximum lateral displacements ranging from 0.07% to 0.22% of the excavation depth (H) and maximum ground surface settlements between 0.05%H and 0.25%H. The maximum surface settlement occurs within a region 0.5-1.5 times the maximum wall deflection. The region from 0 to 0.75 H distance from the retaining wall represents the maximum area of surface settlement, with the affected zone extending up to 4.0 H due to the influence of adjacent excavation construction. Significant spatial corner effects are displayed by the square excavation pit. Influenced by the pit's corner effects, pipelines and buildings near the midspan of the pit experience greater subsidence, resulting in an overall subsidence pattern with the most severe settlements occurring near the planview middle of the retaining system.