Integrated Use of PHC Pipe Piles as Foundation Piles and Excavation Support Columns: Connection Design, Local Finite Element Analysis, and Field Performance Monitoring

Deep excavations in soft ground commonly use permanent foundation piles and temporary support columns as independent systems, causing duplicated construction and discontinuous force transfer. This study proposes an integrated pile–column system in which prestressed high-strength concrete (PHC) pipe piles serve as both permanent foundation piles and temporary excavation support columns. The main scientific contribution is a constructible load-transfer framework for this dual-purpose use. Two steel transition details were developed: a steel sleeve connecting the PHC pile to the steel transfer beam, and a steel transfer structure connecting the pile to the base slab. Together, they establish a continuous column–beam–strut load path. Local three-dimensional finite element models were developed in Abaqus to quantify stress transfer in the critical connection regions under prescribed service-stage actions. The maximum sleeve shear stress and beam axial stress were 27.92 and 112.56 MPa, respectively. The corresponding gross-section elastic bending stress in the PHC pile was 7.48 MPa. The models characterize local connection responses; staged excavation and soil–structure interaction were outside their scope. The system was implemented in the Dongcun Road No. 2021G68 project in Nanjing. Third-party monitoring recorded maximum retaining-wall head displacement, deep horizontal displacement, pile column settlement, and strut force of 10.24 mm, 12.59 mm, 0.43 mm, and 658 kN, respectively. All values remained below the project alarm thresholds. The study establishes a field-documented design framework for PHC pile–column integration and identifies the critical connection regions governing local stress transfer.