Static and dynamic loading test of a foundation are carried out to obtain the behavior of a pile and a pile group. A conventional analysis based on the elastic wave theory are modified to obtain the complex rigidity of a pile group and are compared with the test results. It is shown that the analysis based on the conventional elastic wave theory are not enough to predict the dynamic behavior of piles since they do not take into account both the effect of slip and/or separation between the pile surface and the surrounding ground and the nonlinear behavior of the ground near the pile. An element to be put between the pile and surrounding ground is proposed so as to improve the analysis. The characteristics of the new element is represented as a compliance function which can be obtained from a static loading test of single pile
