Research On Settlement Regularity And Influence Analysis Of Construction Parameters In Basement Adding By Floor Underpinning

The basement adding of existing buildings is one of the effective ways to “reduced construction” and “revitalize the stock”,“activate” the underground space and solve the problem of urban parking difficulties.It has the characteristics of comprehensive,difficult construction and heavy responsibility.Since there are few engineering cases available for analysis and the research methods mainly use finite element analysis;it is particularly important to carry out physical model test and three-dimensional numerical simulation research which can quantitatively determine the secondary settlement deformation law of the upper structure in the adding construction and provide a basis for the subsequent analysis of the additional internal force.Through physical model test and three-dimensional numerical simulation,this paper systematically studies the settlement deformation law of the upper frame structure during the basement adding by floor structure underpinning,and the effects of different earthwork excavation methods and different floor foundations on the settlement deformation of the superstructure are compared and analyzed.The main work and achievements are as follows:? According to the settlement deformation law of frame structure under the long-term effect of self-load and the design concepts of “resistance” and “release” in seismic design,the“central shaft type” earthwork excavation plan and the “surround island type” earthwork excavation plan were proposed.On the basis of this,the “concentric square shape”underpinning roof layout scheme was proposed.? According to the technical characteristics of the floor structure underpinning,this paper demonstrates the technical feasibility of the basement adding by floor structure underpinning.Based on this,the physical model test was designed.Using the dial gauge to collect the settlement of columns under various working conditions in the model test,then processed and analyzed the test data through Origin 2018 software.Through the physical model test research,it reveals the settlement law and overall distribution pattern,and qualitatively determines the most unfavorable working conditions and the influence of construction parameters on the basement adding construction,and puts forward relevant engineering proposals,thus contributing to the promotion and application of the floor type underpinning method.? The FLAC3 D finite difference software is used to establish a three-dimensional numerical model,which verifies the rationality and correctness of the model test results,and supplements the calculation of the principal stress variation law of the underpinning systemand the superstructure system.By analyzing the principal stress variation law of the underpinning structure system and the deformation trend of the plastic zone,the dangerous section position of the underpinning member in the basement adding construction is determined.The research conclusions can provide reference for the design,construction and monitoring of similar projects.