Numerical modeling was used to analyze the uplift behavior of normal piles with straight shaft and pedestal piles. The contact problem between pile and soil was solved by direct constraint method. In this procedure

the motion of the bodies is tracked

and when contact occurs

direct constraints are placed on the motion using boundary conditions-both kinematic constraints on transformed degrees of freedom and nodal forces. The Coulomb friction model was used to treat skin friction force of pile shaft. Soil were modeled as parabolic Mohr-Coulomb material. Reasonable initial stress was obtained by using subroutines. The dynamic nonlinear modeling of uplift procedure was done by applying displacement boundary condition on pile top. The result of in-situ full-scale pile test was used to verify the parameter for computation. Then the distribution law of axial force

friction force

displacement and plastic zone of soil around enlarged base were studied.