Abstract: Lateral and torsional movements of the pile group caused by eccentric lateral loading, which would lead to different movement directions of the foundation piles. Therefore, the movement directions of the foundation piles is a key factor to affect the group effect occurred in the pile group. By analyzing the relationship in motion of double piles subjected to the eccentric lateral loading. It was found that the angles between the movement directions of the leading pile and the trailing pile with their connection line, η and θ, were in the range of 0°≤η≤90° and ?90°≤θ≤90°, respectively. Experimental and numerical data showed that the reduction factor was closely related to η and θ, which was used to quantify the pile-soil-pile interaction between two piles. There were a range for the combinations of η and θ in which no interaction occurred between them. Once the pile-soil-pile interaction existed, the influence of the interaction on the trailing pile was typically more significant than that on the leading pile. The concept of p-multiplier, which originally used to define the group effect in laterally loaded pile groups, was adopted to quantify the group effect on pile groups subjected to eccentric lateral loading. The p-multiplier of each pile can be calculated by multiplying cumulatively the reduction factors from all other piles in the group. An empirical formula was proposed to calculate the reduction factor according to the theoretical, experimental and numerical results. Then a calculation method of generalized p-multiplier was proposed. Two examples were employed to demonstrate the rationality of the method.

Key words: eccentric loading, group effect, p-multiplier, reduction factor