Abstract：To investigate the initial post-buckling behavior of socketed filling pile with highrise pile cap being widely used in bridge engineering，the pile shaft is idealized as a partially supported beam on Winkler foundation. And based on the m method adopted by current criterion，the total potential energy of the pile-soil system is set up. Then，by using the principle of minimum potential energy and perturbation approach，the unified variation expression of critical load during initial post-buckling is deduced with the stability of equilibrium path under three assumed conditions and discussed，respectively. The result shows that，the bifurcation points are symmetric and stable or unstable depending on the stiffness ratios of pile to soil，free length at the top and other pile-soil system parameters. Usually，stiffness of surrounding soil helps to bring more stable initial post-buckling equilibrium path. However，when the stiffness of pile shaft keeps constant while the soil becomes weaker，unstable initial post-buckling equilibrium paths tend to happen more often if the pile tip isn′t socketed into bedrock.
