Group Efficiency Ratio of Pile Groups Subjected to Harmonic Vibration

This paper focus on understanding the behaviour of dynamic Group Efficiency Ratio (GER) for different pile groups (3-pile, 2 × 2, 2 × 3 and 3 × 3) under harmonic vibration. The coupled vibration tests are conducted on the pile foundation in the field for varying eccentric moments (0.868, 1.269, 1.631, 1.944 Nm) to obtain the dynamic responses for all the pile groups considered. The pile groups are constructed in field with hollow steel piles of outer diameter 0.114 m and length 3 m. By utilizing continuum approach, theoretical studies are conducted for perceiving the frequency-amplitude responses of all the pile groups. The theoretical responses are found to be well-matched in comparison with the experimental responses. From numerical analysis, the stiffness and damping of all the pile groups has been also established and subsequently GER of the stiffness and damping has been computed which is the ratio of stiffness or damping of pile group to the sum of stiffness or damping of individual pile. The results exemplify that GER for stiffness is reduced below unity, which indicates the reduction in pile group stiffness due to dynamic pile-soil-pile interaction as the number of piles in group increases.