Investigating the Nonlinear Response of 2 × 2 Pile Group Under Vertical and Coupled Harmonic Vibrations Through a Holistic Approach of Experimental and Numerical Analysis

The present study emphasizes in the anticipation of factors responsible for the nonlinear dynamic response of pile foundations under different modes of rotating machine (high pressure pumps, turbo generators, etc.)-induced vibrations by utilizing both experimental and analytical methods. Forced vibration tests have been performed on a 2 × 2 pile group constructed with hollow steel piles of lengths 5.8 m and outer diameter of 0.166 m for both vertical and coupled modes of vibration. The frequency–amplitude responses and the soil–pile separation lengths of the 2 × 2 pile group are measured from the dynamic pile tests for different eccentric moments under a static load of 15 kN. Due to nonlinearity, resonant frequencies are decreased from 42.97 to 38.33 Hz for vertical mode and 14.10–11.13 Hz for coupled mode, from lower to higher eccentric intensities considered. Using the experimental separation lengths, numerical analysis is performed with continuum approach, for vertical and coupled modes of vibration separately. From the analysis, the feasible choices of boundary zone parameters are ascertained by comparing the frequency versus amplitude responses of dynamic tests and analysis. It is observed from the results that the continuum approach analysis is very reliable to determine the nonlinear dynamic responses of the pile group for vertical as well as coupled mode of vibrations. The numerical analysis has also been utilized to study frequency variation with impedance parameters of the pile group under different modes.