Study On Properties Of Large Diameter Steel Jacking-Pipe During Construction And Operation

Steel jacking-pipe is more and more favored in underground pipeline projects due to its good confinement and material properties.Steel jacking-pipe is developing towards large diameter,long distance and deep overlay.Pipe loading becomes more complicated,so the stress situation of pipe is not quite clear,which not only requires higher construction technology,but also puts forward higher requirements on the mechanical analysis of the pipe.This article relies on the connection project of water source in the upper of Huangpu River,and uses numerical simulation and on-site monitoring method to study the mechanical and deformation of the jacking-pipe under construction and temperature load.The main research findings are summarized as follows:(1)Studying the mechanical properties by the method of two-dimensional and three-dimensional numerical simulation.The pipe-soil interaction of large diameter steel pipe and the pipe stress are analyzed under different thickness of overlaying soil and different construction conditions.The result indicates that longitudinal friction on the contact surface at the top and bottom of the pipe is larger,and smaller on the sides.Circumferential friction at the top and bottom of the pipe nears zero,and the stress on both sides of the pipe is larger,the positon where there is maximum circumferential friction has a certain angle with the vertical.The soil pressure distribution changes after the support of the pipe.When the depth is shallow,the pressure difference between the top and bottom of the pipe is large.When the depth reaches 3 times of pipe diameter,the pressure of the top and bottom soil is little different.With the cross-section away from the machine head,the longitudinal stress becomes larger and larger,and the longitudinal stress near the head increases relatively slowly.(2)Analyzing the variation of jacking force under different construction conditions,the influence of pipeline deviating from design axis on the stress of pipe and the change of stress under jacking and unloading jacking with on-site monitoring methods.The result shows that under actual conditions,there is a strong linear correlation between the jacking force and the heading distance,the average friction force obtained by monitoring is smaller than the standard design value.Axial deviations lead to eccentric load on the pipe,resulting in longitudinal stress on one side of the pipe increasing,and compressive stress on the other side decreasing.When the eccentricity is serious,even tension and pressure change occurs,and the axial deviation has little effect on the circumferential stress.Longitudinal stress away from the machine head is larger,and the numerical analysis results are consistent.(3)Establish the numerical model considering the pipe-soil interaction by the finite element method and combine the on-site monitoring data,the circumferential and longitudinal stresses of the pipe under different constraints were analyzed.The result suggests that constraint condition has serious influence on pipe stress.Restrained release effectively reduce the temperature stress by more than 70%.The socket joints are recommended in the actual project.The circumferential and longitudinal stress near the pipe end constraints Changes about 25 MPa with the temperature difference of 6.5 ℃.This result is consistent with on-site data.It is recommended to take insulation measures in the pipe end.