Theoretical Analysis And Finite Element Simulation Of Pipeline Structure In Liquefied Soil Layer

When soil liquefaction occurs under the action of earthquake,it will cause deformation and destruction of buried pipelines.In view of the floating phenomenon of buried pipelines in liquefied soil layer,the mechanical properties of buried straight pipes,tee pipes and variable diameter pipes under liquefaction were analyzed by combining theoretical analysis and numerical simulation,and the deformation mechanism of pipe sections under the action of thermodynamic and fluid-structure coupling was discussed on this basis.The research work carried out and the main research results obtained are as follows:(1)Based on the Pasternak foundation model,the mechanical analysis model of pipeline uplift reaction in soil layer is simplified,and the force analysis method of straight pipe in soil liquefaction is established.The results show that Pasternak foundation model can better simulate the transfer of soil forces in the non-liquefaction zone than the elastic foundation model.The larger the length of the liquefaction zone is,the larger the floating displacement and axial stress of the pipeline are.The thicker the pipe wall,the smaller the displacement and stress response of the pipe segment.The results showed that the Mises stress at the liquefaction center and the Mises stress at the transition between the liquefaction zone and the non-liquefaction zone increased with the increase of the foundation reaction coefficient and the decrease of the deflection and bending moment of the pipe section.The results showed that the Mises stress at the center of the liquefaction zone and the Mises stress at the transition between the non-liquefaction zone and the liquefaction zone increased with the increase of the shear stiffness and the deflection and bending moment of the pipe segment.The results were compared with those from literature and numerical simulation.(2)The contact model of pipe and soil and soil spring model,simulated the liquefaction area and liquefaction area of the pipe soil interaction,consider the transition zone of soil liquefaction,on the basis of the buried under the soil liquefaction tee section,numerical simulation of variable diameter pipeline section is carried out to explore different pipeline parameters and soil parameters on the mechanical properties section.The results show that when the pipe section is floating,the stress concentration at the junction of the tee pipe section is more likely to be destroyed.The results showed that the axial stress and Mises stress of the reduced diameter pipe segment were larger than those of the coarse pipe segment in the liquefaction zone.The rising displacement,axial stress and Mises stress increased with the increase of pipe pressure and diameter.The increase of buried depth and wall thickness of pipeline is beneficial to reduce the rising reaction of pipeline.(3)Considering the influence of pipeline operating temperature on the floating reaction of buried tee pipe section and variable diameter pipe section in site liquefaction,finite element numerical simulation was used to explore the mechanism of expansion deformation of pipe section,and the influence of different temperatures and internal pressures of different pipe sections on pipeline deformation and stress was analyzed.It is found that the thermal expansion force caused by operating temperature makes the maximum stress appear in the anchoring section.With the increase of temperature and internal pressure,the upward displacement,axial stress and Mises stress of tee pipe and variable diameter pipe increased.(4)Based on the fluid-structure interaction equation,the finite element analysis software to establish three links section and variable diameter pipe section of fluid-solid coupling model,and contrast analysis of the hollow tubes,pipes,considering fluid-structure coupling pipe mechanical properties of three different model,explores the different liquid flow rate and fluid density on section floating displacement and the Mises stress influence.The results show that the floating displacement,axial stress and Mises stress of buried tee pipe and variable diameter pipe increase obviously when fluid-structure interaction is considered.The higher the flow velocity was,the lower the Mises stress and the lower the fluid density was,and the higher the Mises stress was.The velocity in the reduced diameter section increased,the floating displacement and Mises stress increased,while the Mises stress decreased.The fluid density in the reduced diameter section decreased,while the upward displacement and Mises stress increased.