Pile-Soil-Pile Interaction In Pile Groups Subjected To Eccentric Lateral Loading

With rapid development of the ocean economy in China,many offshore structures, such as bridge bents, platforms and wind turbines, have been constructed. The foundations for these offshore structures, which are commonly pile groups, are subjected to lateral loading of considerable magnitude, such as wind and wave action, or ship impacts. Significant torques can be transferred to the pile foundation by virtue of eccentric lateral loading. The lateral and torsional combined loading gives rise to complicated response of pile foundations. However, up to now, knowledge on the response of pile groups subjected to eccentric lateral loading is much limited.In this study, pile-soil-pile interaction between two piles with different moving directions was studied through theoretical analysis, centrifuge model tests and FEM analysis. A facter was defined to describe the reduction of the resistance of a pile group. The variation of the reduction factor with the moving directions of two piles, the calculation method of p-multiplier in pile groups, and the numerical method of pile groups subjected to eccentric lateral loading were discussed in details.It is found from this study that there exists an instantaneous twist center in pile groups subjected to eccentric lateral loading. The relationship of movements of two piles is analyzed based on the concept of instantaneous twist center. A critical angle, beyond which the interaction can be ignored, was found to exist between two piles from wedge-type model. Lateral load tests of two piles in different moving directions were conducted in sand using centrifuge to investigate the effect of η and θ on load-displacement curves of two adjacent piles with3D pile spacing. Numerical modeling based on FEM method was also performed to study the pile-soil-pile interaction between two piles with η=0°,45°and90°. The influences of pile spacing and friction angle on the reduction factor are also studied. An empirical approach was proposed to calculate the reduction factor as η,θ and pile spacing are given. Then, a the calculation method of p-multiplier are proposed and three examples are given in this study. A numerical model has been developed based on the concept of instantaneous twist center, procedures were also illustrated as the soil surrounding pile is modeled as linearly elastic springs ("m" model) and p-y curves, respectively.