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Title: Efficiency of Pile Groups Under Dynamic Loads

Author(s): O.S. Ali Ahmed

Publication: Symposium Paper

Volume: 348


Appears on pages(s): 70-88

Keywords: Pile group, soil pile interaction, machine foundation, pile group dynamic stiffness, pile group damping, efficiency factors.

DOI: 10.14359/51732680

Date: 3/1/2021

Dynamic pile group effect can either increase or decrease the response of pile-supported structures. This paper presents the results of a three-dimensional finite element model of the pile-to-pile interaction that considers the effect of the surrounding soil to determine the dynamic stiffness and damping for vertical end bearing pile groups subjected to vertical harmonic loading. The results were generated for a wide range of the dimensionless frequency parameter (ao) for a 9x9-pile group with three different spacings: 2-, 4-, and 6-pile diameter. Both the stiffness and the damping showed an oscillatory behavior with the dimensionless frequency parameter ao, as well as with the soil shear modulus. Also, the group efficiency was determined as a function of the pile spacing and the soil shear modulus. The efficiency factor for the stiffness can be as high as 1.15 and as low as 0.7 and for the damping as high as 3.75 and as low as 0.4 as a function of the dimensionless frequency parameter ao.