Study On The Influencing Factors Of Lateral Instability Of Circular Underground Diaphragm Wall

With the rapid development of China's economy,the speed of infrastructure construction and urban underground space development is accelerating,and the number of foundation pit projects is increasing,and they are developing towards the direction of deep and large foundation pits.Circular foundation pit is one of the important forms of foundation pit in practical engineering because of its reasonable force,small deformation and ease of excavation.At present,the design of circular foundation pit supporting structure mainly emphasizes the checking calculation of structural strength.However,for the circular foundation pit supporting structure with a small ratio of thickness to radius(referred to as thick-diameter ratio),it is likely to have lateral instability before the strength failure,that is,buckling failure.However,there are few studies on this issue at present,and the stability of foundation pit is related to the safety production and social benefits of engineering construction.Therefore,this paper mainly studies the lateral instability of circular diaphragm wall(hereinafter referred to as circular diaphragm wall).On the basis of summarizing the existing research on the lateral stability of circular diaphragm wall,this paper firstly elaborates the strain stress calculation method of circular diaphragm wall,applies the moment theory of cylindrical shell to circular diaphragm wall,and obtains the analytical solution of internal force and displacement.Then,the potential energy balance equation and stress balance equation of cylindrical shell are summarized by using the stability theory of plate and shell and the energy method,and the model of circular connecting wall is simplified.On this basis,the critical load of instability is deduced,and the calculation formula of critical load of instability is obtained.Finally,based on the theoretical calculation formula,the influence of various factors on the lateral buckling critical load,buckling mode and maximum displacement of circular geotextile wall is further analyzed by using the results of ANSYS finite element eigenvalue buckling analysis,which has a certain guiding significance for engineering practice.The main research work of this paper is as follows:1)The calculation method of stress and strain of circular diaphragm wall is analyzed,and the basic differential equation of cylindrical shell is deduced through the theory of moment of thin shell.Based on this,the reasonable assumption is introduced and the calculation formula conforming to the stress characteristics of circular diaphragm wall is deduced.2)base even wall thickness is far less than the characteristics of the radius and length,choose the stability of plate and shell theory and energy method,summarizes the cylindrical shell buckling equation,and assuming that the displacement function,even the wall plug in buckling equations are derived,get round to connect wall instability critical load calculation formula,laid a theoretical basis for the analysis of the influence factors of follow-up.3)By using numerical simulation method,three basic models of circular diaphragm wall under different stress conditions were established through ANSYS,and the buckling analysis of eigenvalues was used to calculate the buckling critical load,buckling mode and the position of maximum displacement of circular diaphragm wall.4)Through numerical analysis under different strata parameters,wall thickness,wall radius,wall length,embedded depth,wall parameters and different stress states,the changing rules of the critical load,the instability mode and the maximum displacement are obtained.In this paper,through theoretical deduction and numerical analysis reveals that the circular to the wall of the buckling critical load and buckling mode change rule,through the parameter analysis,summary of circular underground continuous wall lateral instability of the modal characteristics and the calculation formula of instability critical load,for circular even wall stiffness design provides a theoretical basis and numerical analysis,to provide theoretical guidance and reference for practical engineering.