Abstract: The authors propose a double-layer composite straight beam model that incorporates the Euler beam theory and the state space method to account for the nonlinear interaction between concrete core, cement soil, and surrounding soil interfaces. This model allows for convenient derivation of general solutions for internal forces and deformations for different combinations of piles in layered soil. By employing the state space method, the model effectively considers soil-structure interactions and variations in local structural parameters when analyzing composite piles. To validate the proposed solution, field test results and numerical analysis findings from existing literature are compared. The obtained analytical solution aligns well with these validation sources. Additionally, using the derived analytical solution, the authors investigate the effects of various pile parameters on pile loading responses. Specifically, they analyze the impacts of pile diameter ratio, core length ratio, and Young’s modulus of the cement soil. The results indicate that increasing the diameter ratio reduces pile settlement and increases pile bearing capacity due to enhanced total side friction resistance and tip resistances. Increasing the core length ratio also leads to higher pile bearing capacity with an increasing growth rate. However, the Young’s modulus of the cement soil has a negligible influence on pile bearing capacity.

Key words: concrete cored-cement soil composite pile, axial loading, pile–soil interaction, Euler beam, state space method