Improper foundation designs for machine vibrations can result in machine failure, severe discomfort to workers around the machine or excessive settlement. The goal of foundation design for machine vibrations is to minimize vibration amplitude. In poor soil conditions, pile foundations are used to support the machine. Soil-pile stiffness and damping must be known at the level of the pile head. Since piles are used mostly in a group, it is also necessary to determine the interaction of the piles within the group. This study uses a 3D finite element method to study the response of pile foundations subjected to vertical dynamic loading. It uses Lysmer’s analog where the pile is replaced by a single degree of freedom dynamic system that provides frequency independent parameters.

A parametric study is performed to obtain the value of the stiffness and the damping of a single pile for different soil properties and for both homogeneous and inhomogeneous soils. Floating and end-bearing piles were also studied. Pile group response is influenced by the soil-pile-soil interaction. The interaction is obtained by varying both the spacing and the soil properties around the pile. Interaction between the piles causes reduction in the stiffness and damping of the soil-pile system compared to an isolated pile. The study provided the interaction factors as a function of pile spacing and properties of the soil. Using the interaction factors, the response of a group of piles can be determined from the response of a single pile.