The earthquake response of a structure on group of piles is investigated. The test model, which is employed in this study, is a foundation on four piles. Three conditions are prepared for examination of the contact effects of the foundation bottom and the backfilling effects on dynamic characteristics of the foundation on the piles. Forced vibration tests are carried out for ascertaining the impedance functions as the inertial interaction, and earthquake observations for the earthquake input motion as the kinematic interaction. On the basis of the test and the observation results, the correlation analyses are executed for examining the applicability of the analytical method based on the substructure method in which the three-dimensional wave propagation theory is applied for calculation of the Green\u27s functions. The analytical method is concluded to have sufficient applicability for the practical design procedure of a structure on pile group
