Response And Effect Factors Of Pile Groups Subjected To Eccentric Lateral Loading

Pile groups are commonly used in bridges, platforms, transmission towers, and offshore wind turbines, which are usually subjected to winds, waves and ship impacts. These actions induce significant eccentric lateral loadings to the pile foundations beneath the structures. The pile groups simultaneously occur horizontal displacement and torsion because of the randomness of the location and direction of the applied loads. The induced internal forces and pile-head displacements among the group piles are quite different to each other. For a pile group subjected to eccentric lateral loads, as the largest internal force among the group piles exceeds the pile capacity, the pile fails and the applied loads redistribute in the rest piles, which finally induce the collapse of the pile group.In this paper, assuming an elastic ground, an approximate approach was developed to study the response of the pile group under eccentric lateral loading. In this approach, some pile-soil-pile interactions were involved:(1) interactions between two laterally loaded piles and (2) interactions between laterally loaded piles and torsionally loaded piles. The first kind of interaction is again divided into an interaction between two piles subjected to parallel loadings and an interaction between two piles subjected to perpendicular loadings. Solutions of single pile subjected to lateral loading and torsional loading provided by Randolph was applied in the approach. The model was further expanded by involving Randolph’s solution on pile group subjected to axial loading. This expansion make the model analyze pile groups subjected to more complicated loading combination and easy to use in engineering design.The model has been used to study the effects of pile-soil-pile interaction, loading location and direction, pile group parameters and ground parameters on response of pile group subjected to eccentric lateral loading. The worst combination of location and direction of applied loading were discussed. The effect of the pile cap rotation on response of the pile group was also studied using the expanded model.It was found that the pile-soil-pile interactions significantly decrease the lateral capacity of a pile group and increase the non-uniformity of the pile-head shear forces and horizontal displacements among the group piles. The effect on torsional resistance of a pile group varies with group size. In addition, pile-soil-pile interactions is one of the reasons of the inconsistence of pile-head shear force and pile-head displacement on each pile in a pile group in direction. The horizontal displacement and twist angle of pile groups subjected to eccentric lateral loading decease with pile spacing, while the differences among the pile-head shear forces of the individual piles in the pile groups also decrease with pile spacing. However, the horizontal displacement and twist angle of pile groups subjected to eccentric lateral loading increase with free standing length, while the differences among the pile-head shear forces of the individual piles in the pile groups decrease with free standing length. It is also found that pile cap rotation significantly increases the horizontal displacement of pile groups and becomes another reason of the inconsistence of pile-head shear force and pile-head displacement on each pile in a pile group in direction.Group configuration has important influent on the response of pile groups with the same number of piles. For pile groups with a square configuration, the internal forces among the pile group is more uniform than other configurations. For pile groups in which the individual piles are triangularly arranged, the lateral stiffness may be greater than pile groups with a square configuration in a particular direction, but the difference of the internal forces among the individual piles is much larger than other configurations. The lateral stiffness of pile groups with circular configuration is uniform in any direction but the uniformity of the internal forces among the individual piles is worse than that in pile groups with a square configuration. Pile groups with individual piles irregularly arranged should be avoid because of the nonuniformity of the their internal forces.Location and direction of the lateral loading influence the distribution of the applied loading among the individual piles in a pile group. There exists an worst combination in which the pile group fails due to that the pile-head shear force of an individual pile in the pile group reach its capacity. Generally speaking, for pile groups with individual piles uniformly arranged, the worst location of the applied lateral load is at the comer of the pile cap and the biggest shear force is always occurred on top of the pile nearest the loading location. For pile groups with square configuration, the worst location of the applied lateral load is at a comer of the pile cap and the worst direction is perpendicular to the diagonal crossing the loaded comer.