The purpose of this thesis is to simulate the behavior of non-connected pile raft system under static and dynamic loading. The previous studies in this field are mostly related to the case that the cap not connected to the soil and there is a layer of different materials such as granular particles used for the separation of the cap from piles. The new idea for this study is to have a gap between the cap and the piles head instead of having granular particles. The first part of this study is for determining the best distance between the cap and piles in order to have the desirable operation of the system. Furthermore, the effect of geotechnical parameters on the behavior of this system was discussed and compared with the connected pile raft system. In the second part of this study, the horizontal impedance function of the system under dynamic loading for the connected and disconnected systems were derived and the effect of the existence of gap was examined. The package FLAC3D and the numerical finite difference method were used in this case. Results demonstrate that the existence of the distance between cap and pile may cause an increase or decrease the bearing capacity of the system. The bearing capacity of piles was decreased when there is a 1cm gap between pile and cap. But by increasing this distance to the definite value we found out the bearing capacity of the foundation were increased. Also, by increasing the distance between the cap and the head of the pile, the amount of foundation settlement before the connection between the cap and the head of pile is increased, which should be less than the allowable settlement. The effect of using the gap between the cap and the pile head on the damping and stiffness of piles was investigated. The result shows that the settlement of the cap before joining to the piles cause the increase in damping and stiffness of the system. Keywords: non-connected pile raft, static loading, dynamic loading, gap, cap