Micropile groups are commonly used as a foundation support in many applications in geotechnical engineering. This study presents a three-dimensional finite element analysis of micropile group model subjected to vertical dynamic loads from a machine foundation. A modified Drucker-Prager constitutive model was used to simulate the nonlinear behavior of the soil as well as the soil-micropile interaction. The soil continuum was modeled using solid continuum elements in the FEM model, while micropiles were represented using beam elements and appropriate interaction properties were assigned to the interface elements. The accuracy of the model developed was verified by its application to the published experimental data.A series of parametric studies were conducted to examine the effects of different parameters on the behavior of the soil-micropile system, including soil nonlinearity, inclination angle, spacing of the micropiles in the group, soil shear/micropile stiffness ratio, machine foundation mass, and the frequency content of the applied load, etc. The obtained results offered valuable insights into the influence of each parameter on the response of micropile groups. The results of these studies demonstrated the effectiveness of the modified Drucker-Prager constitutive model and the three-dimensional finite element analysis in predicting the behavior of micropile groups under dynamic loading. This study contributes to advancing the understanding of the behavior of micropile groups and their interaction with soil under vertical dynamic loading conditions, and it provides criteria for an improved design of the micropile groups under machine foundation loads.

Keywords: micropile groups, machine foundations, three-dimensional finite element analysis (3D FEA) , modified Drucker-Prager, soil-micropile interaction.