Dynamic Response Characteristics of Pile Group Under Axial Harmonic Loading

This study is intended to check the performance of linear and nonlinear theories to determine the dynamic characteristics of the pile supported machine foundations. Forced vibration tests are performed in the field on a 3-pile group having pile length of 3 m and outer diameter of 0.114 m subjected to axial harmonic loading. The dynamic tests are performed for four different eccentric moments under a static load of 12 kN. The frequency-amplitude responses are measured for each eccentric moment. Theoretical study is also performed using both the linear and nonlinear solutions which are based on continuum approach method. The theoretically predicted frequency-amplitude responses are compared with the dynamic field test results for all the eccentric moments. It is found that the predicted responses of the linear solution indicate lower values of the resonant amplitude and much higher values of the resonant frequency as compared to the test results. In the case of nonlinear solution, the predicted dynamic response curves are reasonably well matched with the tests results. Such agreement with the nonlinear analysis results are achieved by considering precise values of boundary zone parameters and soil-pile separation lengths.