Field experiments are conducted on two groups of piles supporting rigid foundations and subjected to harmonic loading. The objective is to investigate the ability of linear elastic theories of pile-group modeling to predict the responsecurve characteristics including the resonant frequency and amplitude. The first pile group consists of six steel pipes of length 3.05 m and outside diameter of 0.102 m driven in a layer of cohesionless soil. The second group consists of six cast-in-place concrete piles 7 m in length and 0.32 m in diameter