Investigation of pile group effect subjected to influence of pile arrangement and pile stiffness

The additional pile method is a technique to reinforce existing foundations by piles and footings.This additional reinforcement is a seismic reinforcement method for foundations.In this method, the mechanical behavior becomes more complex than for common pile groups because an existing foundation is combined with piles that are of a different diameter and material.The main reason that it is difficult to understand the mechanical behavior is the pile group effect, i.e., the interaction of the pile-ground-pile.A solution for this pile group effect has been approached in the past.Poulos (1964) considered the following major factors: (1) spacing between piles, (2) degree of fixation at the pile head, (3) arrangement of the piles and (4) relative stiffness between the piles and the ground.However, these factors are unclear for the additional pile method and result in difficulties when calculating the pile group effect.The aim of this study is to clarify the pile group effect of additional piles as the first step in a design confirmation.First, a simulation analysis of a past centrifuge model test on a horizontally loaded two-pile group is conducted to confirm the accuracy of the simulation for the interaction between two piles.Subsequently, a parametric analysis changes the pile arrangement and pile stiffness.The load share rate of each pile and the pile group efficiency are discussed.