An analytical load-transfer model for pipe-stiffened deep cement mixing piles under axial loading

Pipe-stiffened deep cement mixing (P-SDCM) piles, formed by inserting a precast concrete pipe pile into a DCM column, are widely adopted for soft ground improvement. While experimental testing and numerical simulations on the axial response of P-SDCM piles have been reported, an analytical solution that explicitly accounts for multi-interface load transfer remains limited. This study proposes an analytical model for predicting the displacement and load transfer of P-SDCM piles under axial loading, in which the composite pile system is explicitly decomposed into the in-core DCM, the pipe, the out-core DCM and the associated three interfaces, each governed by non-linear interfacial shear models capable of capturing post-peak softening. A robust displacement-controlled iterative algorithm is established to obtain the displacements, axial force and interface shear stress of each component. The analytical solution is validated against physical model tests and three-dimensional continuum finite-element analyses. The results show that the model reasonably captures the load–settlement response and load transfer among pile components. Parametric analyses were further conducted to quantify the influence of geometric and material properties on axial responses of the pile. The practical recommendations for the optimised design were provided based on parametric analysis.