Analytical Studies On Dynamic Interaction Factors And Vibrating Responses Of Pile Groups

Piles are always used in practical engineering application to reinforce soft foundations.Design of pile groups embedded in soil layers requires accounting for how each pile interacts with its surrounding soil,i.e.pile-soil interaction,but also for interaction between piles of the same group,i.e.pile-pile interaction.The effects of soil-pile and pile-pile interaction phenomena on load transfer mechanisms are coupled,and are collectively referred to in the literature as pile-soil-pile interaction effects.A popular superposition principle which allows considering effects of pile groups are widely used to evaluate the dynamic responses of pile groups with an arbitrary of members.However,this popular method included some basic assumptions,such as neglecting effects of receiver pile vibration on the source pile,ignoring geometric effects of piles,ignoring the interaction between soil layers.However,the applicability of some assumptions still remains to be evaluated.Deficiencies of the current superposition principle are analyzed based on the large scale model tests of pile-soil-pile vertical interaction.Accordingly,this thesis proposed analytical models to improve the classical method of pile-pile interaction,including the following aspects:(1)Several large-scale model tests are conducted to study the pile-soil-pile coupled interaction under vertical dynamic loads.Vertical displacement,dynamic soil pressures and pile strains are recorded to analyze the load transferring mechanism in the pile group.Some selected results of the model test are analyzed to summarize shortcomings of the current analytical method,and further to provide research ideas for the following part.(2)A new analytical model for calculating the vertical or horizontal dynamic impedance of pile groups with arbitrary members is presented in this paper.The derived solution allows considering robustly the effect of pile-to-pile interaction on the impedance of the group,by accounting for the secondary waves generated by the vibration of the receiver pile,and how these alter the response of the source pile.This is achieved by introducing a modified expression for the pile-to-pile interaction factor through defining a coupling factor between the source pile and the receiver pile.(3)When the active pile is activated by vertical or horizontal loads,the soil attenuation function is derived analytically through simulating the soil as a three dimensional continuum by using Laplace transformation.And then,the interaction factor,which is defined through two pile displacement,is obtained analytically.Some selected numerical examples are presented to clarify the effect of the introduced refinement on the popular interaction factor.This analytical results are further popularized to saturated soil layers.(4)The classical pile-to-pile interaction factor is modified to consider the geometry effect of the pile group,in which the soil layer is still simulated as a three dimensional medium with single phase.The stress distribution field under vertical or horizontal loads is obtained by Laplace transformation to define the new pile-to-pile interaction factor through aspects of pile resistances.Accordingly,the influence of pile radius on the proposed pile-to-pile interaction factor is analyzed through some examples.And then,the pile-to-pile interaction factor which is capable of considering the pile geometry effect and embedded in the soil layer with single phase is extended to that in the saturated soil layer.(5)The classical pile-to-pile interaction factor generated by the applied vertical or horizontal loads,which allows considering three-dimensional wave effect of the soil layer,is utilized to evaluate the vertical or horizontal dynamic responses of the pile group.The analytical solution for pile groups embedded in three dimensional layers is accordingly derived based on the superposition principle of the pile displacement and boundary conditions.(6)The proposed interaction factor for piles subjected to vertical or horizontal loads,which allows to considering the pile geometric effect,is adopted to study the vertical or horizontal dynamic responses of pile groups embedded in soil layers with single phase.Considering the superposition principle of soil resistance and boundary conditions,vertical or horizontal dynamic responses of the pile groups can be derived,which accounts for effects of pile geometry on corresponding responses of the pile group.Accordingly,selected examples are presented to clarify this refinement on the complex impedance of the pile group.Next,the proposed pile-to-pile interaction factor is extended to analyze vertical or horizontal dynamic characteristics of pile groups embedded in three dimensional saturated soil layers.