Influence Of Tunnel Excavation On The Bearing Capacity And Settlement Of Adjacent Pile Foundation

Underground space exploration and utilization is one of the main approaches to deal with issues of population,transportation and environment along with rapid urban development.For design of underground space and coordinated development with superstructures,construction of tunnels and underground pipe for urban underground transportation system has become an indispensable part of urban development in China.With the increasing buildings and extended distributions in complex environment,it is inevitable to have crossing or nearby projects during tunnelling,and the tunnelling induced ground displacement and stress release will inevitably lead to settlement and failure of adjacent piles,affecting the security and global stability of the surrounding structures.This dissertation summarizes the literature on tunnel-pile interaction and cavity expansion theory and its engineering applications.In order to solve the problem of tunneling adjacent to pile foundation,the influence of tunneling on the bearing capacity and settlement of existing single pile was studied through analytical solutions of cavity expansion-contraction in finite medium and three-dimensional numerical simulation.The mechanisms of tunnel-pile interaction were then explored,and the main research contents and achievements are listed as follows:Firstly,based on the Mohr-Coulomb yield criterion and large strain assumptions,the uniform solutions for expansion and contraction of cavities in finite media have been derived,and validated against solutions in infinite medium.Parametric study has been provided for investigation of the effects of soil properties on cavity pressure,plastic region and stress distributions in finite medium.The solutions were also extended to derived for the scenarios with rigid boundary of finite medium,which completed the theory of cavity expansion-contraction in finite medium.Secondly,the predictions of pile bearing capacity and settlement were developed based on the proposed cavity expansion solution in finite medium,showing comparable results with previous calculation and experimental data.Considering the ground free boundary,settlements and displacement fields induced by excavation of shallow tunnel were estimated based on the cavity contraction solution in finite medium.A tunnel-pile interaction model was then proposed for prediction of volume loss induced pile bearing capacity reduction and settlement.Parametric study provided the effects of pile length,pile diameter and tunnel-pile distance on the pile bearing capacity and settlement during tunnelling.The model was also extended to use solutions in CASM model.The criteria of pile bearing capacity,safety factor and settlement were proposed for the evaluation of pile stability during tunnelling.Thirdly,the influence of whole tunnel excavation process on pile bearing capacity and settlement has been studied using finite element method.With considering soil pressure,grouting pressure,grouting hardening process and soil modulus changes in actual working condition during construction,the simulation examined soil horizontal and vertical displacements induced by tunnelling,with various pile length and tunnelpile spacing.Comparisons with analytical results validated the numerical model for investigating tunnel-pile problem.There are 70 figures,5 tables and 91 references in this dissertation.