Interaction factors for pile groups due to downdrag

The group effect which causes different downdrag distribution in individual piles within the group was investigated by using a numerical analysis and an analytical study. The interaction factors due to group spacing, the total number of piles in a group and the relative position of a pile within the group were estimated by using a three dimensional nonlinear finite element approach. An approximate closed form solution was also developed for the single pile case. It was shown that the interaction factor for pile groups varies extensively according to the group spacing, a major parameter influencing the group effect. Based on the results obtained, interaction factors were proposed quantitatively for 9 to 25 piles with spacing to diameter ratios varying from 2.5 to 5.0 for downdrag loads.