Deformation Evolution and Optimization Analysis of Supporting Embedment Depth in Asymmetric Deep Excavations Under Heavy Rainfall from Typhoon Yagi

Typhoons and extreme rainfall significantly exacerbate engineering risks during deep excavation construction. Based on an asymmetric deep excavation project in Hainan under the influence of Super Typhoon Yagi, this study analyzes the evolution of Soil Mixing Wall (SMW) pile deformation and prestressed anchor cable axial forces through field monitoring. PLAXIS 3D 2023.2.0.1059 finite element software is employed to investigate the deformation response of the supporting structure under the coupled effects of excavation and extreme rainfall, revealing the optimal design for embedment depth under such adverse conditions. The results indicate that the presence of existing buildings leads to asymmetric deformation and pronounced corner effects. The synergistic action between the capping beam and the waler transforms the pile displacement profile from a cantilever mode to a bow-shaped distribution. Parametric analysis determines the optimal embedment depth to be 10.6 m and the critical safety embedment depth to be 7.6 m. Under a 400 mm/d typhoon rainfall condition, the maximum horizontal displacement of the supporting structure increases by 1.6–2.0 mm compared to non-rainfall conditions. With a 3.5 m water head, increasing the embedment depth from 6.1 m to 10.6 m reduces the maximum horizontal displacements on the east, south, and west sides by 98%, 42%, and 10%, respectively. This study provides a theoretical basis and practical reference for embedment depth optimization in typhoon-prone regions.