Study On Uplift Response And Seismic Measures Of Buried Natural Gas Pipeline In Liquefied Area

Soil liquefaction is one of the main phenomena of pipeline hazard in strong earthquake area.It often occurs in loose sandy sedimentary strata with high underground water level.The buried natural gas pipeline located in liquefaction area will float up.Which would be a threat to national economy and people's lives and property safety.Therefore,it is of great significance for the treatment and seismic design of buried gas pipelines,in liquefaction areas to establish the correct floating up reaction buried natural gas model of pipeline floating reaction in liquefied area,analyze the law of pipeline floating up,and put forward the aseismic measures.The main contents of this paper are as follows:(1)Making the research methods of floating response of buried pipelines in seismic liquefaction areas at home and abroad,and summarizing the achievements and shortcomings in theoretical analysis and experimental research.Analyzing the harm of earthquake disaster to pipeline,studying the mechanism of sand liquefaction,determining the discriminant mode of sand liquefaction,analyzing the influencing factors of liquefaction,and establishing the criterion for judging failure of buried natural gas pipeline in liquefaction area.(2)Based on the nonlinear finite element theory and shell theory,considering the influence of pipeline pressure and incomplete liquefaction zone,the finite element model of floating response of buried pipeline in liquefaction zone is established by ANSYS Workbench.Three-dimensional shell element is used for pipeline,three-dimensional solid element is used for non-liquefaction soil,and soil-spring model is used for pipe and soil contact in liquefaction zone.The finite element model is validated by previous research results.The variation of displacement,axial strain and von Mises stress during the floating reaction of buried natural gas pipeline in liquefaction area are studied by calculation and analysis of examples.(3)Taking buried natural gas pipeline in liquefaction area as the research object,the effect of parameters such as length of liquefied area,length of non liquefied zone,diameter of pipe,thickness of wall,material,depth of pipeline,axial force of pipeline and natural gas pressure of pipeline on the mechanical behavior of buried pipeline are analyzed.According to the regular pattern obtained,the construction of engineering transformation is proposed(4)In view of the problem that the calculation formula of floating displacement and axial strain of buried pipeline in liquefaction area are only applicable to hot oil pipeline,which is provided in the Technical Code for Seismic Engineering of Oil and Gas Transmission Pipeline Engineering(GB50407-2008),the simplified formula for calculating the maximum floating displacement and maximum axial strain of buried pipeline in liquefied area suitable for large pipe diameter and high pressure natural gas pipeline are obtained and verified in this paper.(5)From preventing soil liquefaction and preventing pipeline floating in liquefaction zone,the aseismic method of buried natural gas pipeline in liquefaction area is analyzed.The aseismic design flow of long distance natural gas pipeline is put forward.Simulation the floating response of buried pipelines,analyzing the influence of piers' spacing and piers along the axial length of pipelines against the effect of uplift.In view of the problems of high cost and long period in the traditional reconstruction method of buried pipeline in liquefaction area,this paper puts forward the reconstruction measures of "local block method",and analyze the effects of the number of blocks and the weight of the blocks on the suppression of pipeline floating.(6)The monitoring system of buried natural gas pipeline in liquefaction area is designed.The system consists of four parts:monitoring sensing subsystem,data acquisition and transmission subsystem,data analysis and processing subsystem and early warning subsystem,which can monitor and warn pipeline strain,operating temperature,strong vibration of soil,tube-soil force,pore pressure of soil of pipeline.