Title: Efficiency of Pile Groups Under Dynamic Loads
Author(s): O.S. Ali Ahmed
Publication: Symposium Paper
Appears on pages(s): 70-88
Keywords: Pile group, soil pile interaction, machine foundation, pile group dynamic stiffness, pile group damping, efficiency factors.
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.