Dynamic Experiments on Two Pile Groups

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 constructed in a clay site. The response is measured at different levels of excitation force amplitudes. Moderate nonlinear behavior is observed. The group stiffness and damping required to generate the theoretical response curves are established using an approximate method based on combining the plane strain soil reactions solution of the single pile with dynamic pile‐soil‐pile interaction factors. The theoretical results are also verified using the more rigorous direct analysis approach. Comparison with experiments shows that the linear theory gives a good estimate of the group stiffness but over estimates the group damping.