Experimental and numerical study of pile foundations subjected to rotating machine-induced coupled excitations

Abstract

ABSTRACT Dynamic response characteristics of a hollow steel single-pile and three-pile group are investigated under coupled vibration. Forced coupled vibration tests are conducted on the piles for static loads of 12 kN and 14 kN under different eccentric moments. The time-acceleration responses are measured for different frequencies for both horizontal and rocking modes and finally the frequency-amplitude responses are determined for horizontal and rocking components separately. The dynamic frequency-amplitude responses of piles are analysed by continuum approach method with two different soil-pile models: (i) a linear visco-elastic composed medium with the consideration of reduced shear modulus and (ii) a boundary zone model with non-reflective interface of shear modulus with parabolic variation. The variation of stiffness and damping of the soil-pile system are also determined. The analytical results are compared with the dynamic test results to verify the applicability of those soil models for predicting the non-linear response of soil-pile system under coupled vibration. It is observed from the comparison curves that the results obtained from the first soil model are found reasonably close to the dynamic test data. However in the case of second soil model, the resonant amplitude values are found much higher than the test data. Based on the analytical results, the boundary zone parameters like modulus reduction ratio, thickness ratio, weak zone soil damping and separation lengths of pile under different eccentric moments are predicted in present field condition. The variations of group efficiency ratio of the pile group with frequency are also determined form the analysis.