Abstract: Aiming at the problem of pile penetration in soft clay, a general solution method using undrained cylindrical cavity expansion model for perfectly drained and undrained cases was proposed. This soil was described by the modified Cam-clay (MCC) model and the partial differential equations for the elastic-plastic cylindrical cavity expansion were presented by combing the kinematics equations, stress equilibrium equations and the mass conservation equations. The similarity solution technique was selected for solving the equations and the semi-analytical solution was obtained. The solution was validated by comparing with the published solutions.