Study On The Influencing Factors Of New Pipe Roof Construction On Soil Deformation In Loess Stratum

In order to improve the underground engineering construction technology of urban rail transit in the loess area and reduce the impact on the ground traffic and surrounding environment,it is urgent to explore the new underground excavation technology suitable for the subway station in the loess area.The new pipe roof method is an auxiliary method of underground excavation construction.The pipe roof structure with integrated support structure can complete the construction of underground space under the condition of reducing the influence of ground traffic,and it has been tried and applied in domestic projects.Using ABAQUS software and referring to the geological data of Yingze Street under the railway station tunnel project in Taiyuan City,the numerical calculation model is established,and the comparison between the numerical calculation results of the project and the ground monitoring data proves that the model calculation results are accurate.The numerical simulation of pipe roof construction under different working conditions is carried out to analyze the variation rule of pipe roof construction in loess area.The main research contents can be divided into the following three aspects:(1)In order to study how to reduce the ground deformation caused by the construction and the stability of the pipe roof pre-erection structure,five construction factors on the soil deformation and the stability of the supporting structure were analyzed and discussed by the principle of single variable.The results showed that:The influence weights of each factor on the ground settlement,horizontal displacement and vertical convergence value from the largest to the smallest are the spacing of ribs,the width of ribs,the spacing of steel tubes,the diameter of steel tubes and the cutting position of steel tubes.Among them,the spacing of ribs accounts for the largest proportion,which reaches more than 50%.When the cutting and welding position of steel pipe is changed,the horizontal deformation of pipe roof structure changes the most.(2)Based on the influence of different construction factors on ground deformation,the stress variation law of pipe roof construction structure is calculated and analyzed.The results showed that:The stress at each point of the steel pipe at different parts of the pipe roof structure increases with the increase of the diameter of the steel pipe or the distance between the ribbed beams,and the two have a positive ratio relationship.The stress at each point of the steel pipe decreases with the increase of the distance between the steel pipe and the width of the ribbed beams,and the two have an inversely proportional relationship.When the steel pipe is welded by eccentric cutting,the stress value of the pipe roof increases,and the stress of the ribbed beam section with small eccentricity is the largest.(3)The influence of pipe roof pre-erection structure and pipe roof ring beam structure during pipe jacking construction on ground settlement and the stress characteristics of pipe roof steel pipe are compared and analyzed.The results showed that:The influence of pipe jacking construction process on ground settlement and final ground deformation is less than that of pipe roof ring beam structure when cutting and welding of pipe roof is used in pipe jacking construction.The stress value of the joints between the steel pipe cutting and welding and the ribbed beam in the pipe roof pre-construction structure is much greater than that of the pipe roof ring beam structure.(4)The differences of soil deformation and stability of supporting structure under different construction factors between arch pipe roof structure and rectangular pipe roof structure are compared and analyzed.The results showed that:No matter the comparison of land subsidence under the same factors,or the comparison of ground deformation law under different construction factors,the rectangular pipe roof structure changes greatly.The structural deformation of the arch ring and the stress of the steel tube in the arched pipe roof structure are less than those in other parts,and less than those in the rectangular pipe roof structure.Through the analysis and study of the above construction factors,the stress characteristics of the pipe roof pre-construction structure and the pipe roof ring beam structure and the influence of construction on the ground deformation are thoroughly discussed,in order to provide a certain reference for engineering application.