Research On Working Behaviors And Deformation Calculation Of Pile Foundation Under Vertical Load

With the rapid development of China’s urbanization,the construction of high buildings and underground buildings(structures)showed rapid development momentum,in view of the control requirements of the vertical bearing performance and deformation,the pile foundation was increasingly widely adopted as the preferred form of deep foundation.Comparing with the single compressive pile,the research of uplift pile and pile group was not very in-depth,and the existing studies were concentrated in the damage modality and ultimate bearing capacity,the working behavior and deformation calculation were few in studies.Up to now,the design method of uplift piles were still in the stage of imitating the design of compressive piles,which resulting in theoretical research was far behind of the engineering practice.On account of interaction of piles behaving very prominent and important in the deformation of pile groups,so that deformation of the pile groups had become the urgent issues in engineering applications.In allusion to the above problem,related studies were carried out to explore the vertical working properties and establish the method of deformation calculation,as well as to dig the bearing potential and improve the theoretical design level of pile foundation,which has theoretical and practical significance.In this paper,the main research aspects carried out were as follows:1.In order to study the influence of single pile displacement caused by uplift pile body’s nonlinear characteristic,the current load transfer models are integrated,the elastic-plastic deformation characteristics of pile body in the uplift process are considered,the transfer iterative analysis method which adapt to the characteristics of single uplift pile is established.The non-linear model of concrete tensile strength was introduced in the analysis method,and the iterative solution of the corresponding displacement is carried out from the pile head.The method overcomes the shortcomings of the previous iterative analysis method,which the side frictional resistance of the pile segment under the critical pile length does not play fully.The analysis method is more reasonable and perfect,which provides a theoretical basis for the uplift pile in the stage of exploration and design.The load-displacement curves obtained by the iterative analysis method in this paper are in good agreement with the measured curves,which have the advantages of simple method,strong applicability and high accuracy.In addition,taking into account the special circumstances which the uplift load is at a certain depth of the ground,therefore,the preliminary study of load transfer of uplift pile with changing load is carried out.2.The nonlinear behavior of the uplift pile with enlarged bottom is studied.Based on the current existing research results of uplift pile with enlarged bottom,and thin wall concentric cylinder shear deformation mode and elastic mechanics theory,the nonlinear analytical expressions of deformation considering pile-soil slip are derived.This makes the analysis of the deformation of the enlarged-bottom uplift pile more reasonable,and the specific calculation steps are given.By comparing with the measured results,it is shown that the nonlinear analytical solution can be used to calculate the nonlinear deformation of the enlarged-bottom uplift pile under the action of the working load.In the end,in order to carry out the analysis of the deformation of uplift pile under more complicated conditions,the solutions is extended to the uplift pile with expanding body.3.Because of the assumption of approximate theory,and the failure of fully considering the influence of mutual reinforcement effect in pile group,the existing calculation methods of deformation of pile group are far behind the engineering practice.In this paper,the concept of "reinforcement effect" is redefined,and the deformation calculation considering the reinforcement effect is studied.Based on the shear deformation mode of thin wall concentric cylinder and elastic superposition principle,a theoretical analytical solution is proposed to consider the influence of mutual reinforcement effect in pile group.At the same time,a three dimensional finite element numerical model is established to simulate the interaction between piles and soil.The theoretical results of the analytical solution agree well with the finite element analysis results and the measured results of the model test.4.In view of the fact that the interaction of uplift pile and compression pile is a very complicated problem,the analytical model of the interaction of the compressive piles and uplift piles is established,and the theoretical study is carried out.With this method,and the theoretical analysis of anchor-pile loading test is carried out,and the load-displacement relationship of compressive piles and uplift pile in three working conditions(working conditions one: uplift pile and compressive pile;working conditions two: two uplift pile;working conditions three: two compressive piles)are calculated and analyzed qualitatively.At the same time,a three dimensional finite element numerical model is established to simulate the interaction between piles and soil.The theoretical calculation results are close to the finite element calculation results and the model test results.It is showed that the theoretical method can be used to analyze the interaction between uplift piles and compressive piles.5.For the imperfections of existing research on settlement of compressive pile group considering reinforcement effect of pile group,this paper makes a thorough research on the deformation calculation theory considering reinforcement effect.And a theoretical method is proposed to calculate the settlement of pile group,which can consider the reinforcement effect of pile group.Based on the shear deformation mode of thin wall concentric cylinder,the analytical solutions of compressive piles considering reinforcement effect of pile group are solved.By comparing with the measured data,the measured value is close to that calculated by the method in this paper,which verifies the correctness of the analysis model of the pile group.The method proposed in this paper overcomes the failure or inadequate consideration of mutual interaction coefficient taking into account the reinforcement effect,which makes the displacement calculation of pile group more accord with the cooperative work characteristics in practical engineering,so it can be used to deformation analysis of large scale pile group.