Research on vertical bearing behaviors of concrete-core cement mixing piles based on a four-dimensional lattice spring model

Concrete-core cement mixing (CCM) piles are an effective ground improvement technique for soft soils, enhancing bearing capacity and material efficiency by introducing a stiff core. However, the mechanisms governing vertical bearing behavior, ground failure evolution, and the influence of key structural parameters remain insufficiently understood. A series of numerical models of CCM piles with varying core lengths and irregular cross-sectional configurations are established using a four-dimensional lattice spring model (4D-LSM). The load transfer mechanisms, the mobilization of shaft resistance, and settlement responses under vertical loadings are systematically investigated. The predicted load–settlement curves and failure patterns exhibit good agreement with laboratory model tests, demonstrating the accuracy and applicability of 4D-LSM. Parametric analyses indicate that core length is a dominant factor influencing bearing performance, with the most significant improvement achieved when the core length is 0.8–1.0 times the pile length. Bamboo-shaped piles significantly enhance shaft resistance by enlarging the pile–soil contact area, resulting in ∼40% increase in ultimate bearing capacity and reduced settlement compared with uniform-diameter piles. Properly designed stepped piles can maintain bearing capacity while reducing material consumption. Optimizing the core length and cross-sectional configuration can effectively enhance bearing performance while improving material efficiency, highlighting the sustainability potential of CCM piles in soft ground engineering.