Research On Key Technology Of Jacking And Connecting Of Shallow Buried Steel Pipe In Pipe-roof Pre-construction Method

With the continuous development of underground space,construction constraints in actual projects have gradually increased,and the construction conditions have become more and more complicated.The previous construction methods cannot adapt to the development of the current underground space structure.As a new type of construction method,the Pipe-roof Pre-construction Method has the advantages of wide stratum applicability and large span of space that can be constructed compared with other construction methods,and can adapt to complex working conditions with more restrictive conditions.However,the current research on the Pipe-roof Pre-construction Method mainly stays at the engineering application stage,and the numerical simulation and surface deformation calculation methods are not yet mature.This article takes the underground space development project under the airport runway on the south side of Daxiaochang Airport Station as the background.According to the project features such as shallow soil covering of the project structure,prohibition of excavation of the surface runway for the protection of cultural relics,and strict control conditions for surface deformation,the Pipe-roof Pre-construction method is selected.Construction,combined with engineering reality,through numerical simulation and theoretical analysis,several key processes in the tube curtain pre-construction method under the super-shallow buried operating condition of the overlying airport runway are carried out through numerical simulation and theoretical analysis: Single steel pipe jacking,Close-packed large-diameter parallel pipe jacking,cutting and connecting between pipes,and concrete pouring of the roof in the pipe curtain are researched.Analyzing the changes in surface deformation and structural internal forces caused by the above procedures,the main research content and results include the following aspects:(1)A simplified finite element model of single-pipe jacking is established to study the process of single-pipe jacking under the super-shallow buried airport runway.The results show that: the jacking of a single jacking pipe causes the surface settlement deformation above the jacking section axis.The horizontal influence range of ground settlement is 10 D,and the longitudinal influence range is 8D,which is larger than other working conditions;with the increase of jacking distance,The maximum surface settlement increases,the vertical convergent deformation of the steel pipe and the extreme value of the steel pipe bending moment increase first and then stabilize.(2)The finite element software is used to analyze the influence of grouting parameters,embedding depth and other parameters on the surface deformation when a single steel pipe is jacked.The results show that synchronous grouting can effectively control the surface settlement when the steel pipe is jacked.The comparative analysis results show that the surface settlement control effect is best when the elastic modulus of the grouting material is 0.5MPa;the maximum value of the surface settlement gradually increases with the soil loss rate and embedment depth increase.(3)Based on the theory of soil arching effect,a reasonable arch axis model is obtained,considering the control conditions of arch toe and vault strength,a calculation formula for the optimal spacing between large-diameter parallel pipe jacking pipes is proposed,and the pipe jacking spacing in the project is optimized based on the actual situation of the project.design.The results show that when using soil arching to optimize the spacing between pipes,the buried depth of the pipe jacking needs to be greater than 4m.(4)The finite element software is used to study the jacking process of large-diameter closepacked parallel pipe jacking under the super-shallow buried operating condition of the overlying airport runway,and the influence of the steel pipe spacing and jacking sequence on the surface deformation is analyzed.The results show that when the large-diameter close-packed parallel pipe jacking is completed,the surface deformation distribution law is related to the jacking sequence,and the interval jacking is the optimal working condition;when the pipe jacking is completed,the surface settlement increases with the increase of the distance between the pipes.(5)Based on the Winkler foundation beam model and peck settlement theory,the concrete runway layer above the soil mass is simplified as an elastic foundation beam resting on the soil mass,and the settlement of the slab bottom soil mass when the runway is not considered is equivalent to acting on the foundation beam The calculation formula for the surface deformation caused by the jacking of the steel pipe under this working condition is proposed;the distance between the pipes under the ultra-shallow buried working condition is classified,and the calculation formula for the surface deformation caused by the parallel pipe jacking under different distances is proposed,and The calculation result of the formula is compared with the finite element result.The results show that the proposed formula can better calculate the surface deformation caused by a single pipe jacking or parallel pipe jacking under this working condition.(6)Establish a cutting and connecting model between two jacking pipes,using the longitudinal cutting sequence,the longitudinal spacing of the supports and the length of a single cut as parameters,to study the influence of the above parameters on the structural force and the deformation of the ground surface.The results show that the cutting and connecting processes between the pipes have little effect on the surface deformation and the vertical convergent deformation of the steel pipe;in actual construction,the single-cycle cutting length between the pipes should not be too large.A simplified cutting connection model between steel pipe groups is established to analyze the influence of the cutting sequence on the surface deformation.The results show that the surface deformation caused by interval cutting is the most stable.(7)The finite element software is used to establish a concrete top slab pouring model in the tube curtain,analyze the distribution law of surface deformation caused by the concrete top slab pouring operation;propose to control the surface deformation through grouting to strengthen the soil,and analyze the influence of the reinforcement depth on the control effect.The results show that: the top slab concrete pouring operation will cause a large surface settlement;the soil and the grouting body form a composite stress system after grouting reinforcement,and the maximum surface deformation decreases first and then stabilizes as the depth of reinforcement increases.This paper uses numerical simulation and theoretical analysis to analyze the single steel pipe jacking,close-packed large-diameter parallel pipe jacking,cutting and connection between the pipes,and the inner roof of the pipe curtain in the Pipe-roof Pre-construction method under the supershallow buried operating condition of the overlying airport runway.Research on concrete pouring operations has made up for the deficiencies of existing research,provided references and suggestions for the actual engineering application of the Pipe-roof Pre-construction method,and laid a foundation for the popularization and application of similar projects.