Abstract: Numerical studies on the forming mechanism of replacement piers are scarce, particularly on the kinetic movement of the reinforcement (the stones) and the deformation of the gravel layers. Previous studies tend to treat the stone layer as a continuum, which does not conform to the reality. The numerical simulation is conducted to study the movement of many stones in the soils during the dynamic replacement process. The deformation and forming process of the reinforcement are modeled as the frictionally contacting circular granules. The dynamic replacement process is also simulated under repeated impacts. The numerical results show the forming process of the reinforcement pier. The movement and the distribution of the stones within the soils can be divided into 4 stages. The numerical simulated of repeating tampings agrees reasonably well with the experimental results in terms of hammer velocity, displacement and acceleration.