Vertical Vibration of Pile Groups

An approximate theory for vertical vibration of pile groups is presented. The theory accounts for dynamic interaction of piles in a group, weakening of the soil around the pile due to high strain, soil layering and arbitrary tip conditions. The theory is used to study the effects of pile interaction on stiffness and damping of pile groups, distribution of internal forces in the piles and response of pile supported foundations to harmonic excitation. The theory indicates that dynamic group effects can considerably differ from static group effects particularly in that the group stiffness and damping can be not only reduced by pile-soil-pile interaction but also increased depending on frequency, pile spacing and the weakening of the soil around the piles. The effect of frequency is much stronger for pile groups than for single piles.