Research On The Mechanical Properties And Damage Of Buried Polyethylene Pipelines Under Ground Subsidence

With the construction and operation of the West-to-East Gas pipeline,the Sichuan-to-East Gas pipeline and the gradual introduction of natural gas pipelines from Central Asia,Russia,Myanmar and other countries and regions in China,increasing cities and towns have laid gas pipelines.The use of natural gas by urban residents is increasing day by day.Polyethylene and its composite pipes are widely used as urban gas pipelines due to their excellent corrosion resistance,excellent welding performance,high flexibility,economic and environmental protection,long service life,low energy consumption in operation and convenient maintenance.China is a vast country with many natural disasters such as earthquakes in the western areas and serious groundwater collection in the eastern area.Land subsidence is frequently caused by natural disasters such as earthquakes or excessive groundwater collection,which will inevitably affect urban gas polyethylene pipelines and even lead to pipeline damage.The polyethylene pipeline is often used for the transportation of low and medium pressure gas in cities and towns.Once it breaks down and fails,it will easily cause serious consequences such as fire and explosion,which will bring great harm to the surrounding environment,the safety of life and property of residents.Therefore,it is necessary to study the influence of ground subsidence on buried polyethylene pipelines,which is of great significance to ensure the safe operation of urban gas pipelines and the safety of life and property of urban residents.The results of this paper can also provide a theoretical basis for the formation of a quantifiable evaluation system for safety assessment and damage of urban gas pipeline network.In this paper,the buried polyethylene(PE)pipeline subjected to land subsidence is studied.The main contents are as follows:(1)Considering the rate dependence of polyethylene,uniaxial tensile tests of polyethylene at different tensile rates were carried out to obtain its constitutive model.Tensile tests of specimens with crack defects were carried out.The extended finite element method was used to simulate the tensile process.In the end,the relevant parameters were obtained.(2)The finite element model of buried polyethylene pipeline under land subsidence is established.Then we analyzed the stress and deformation characteristics of the pipeline under settlement displacement load.Based on the study in the mechanical response of pipeline under different parameters,the quantitative relationship between different parameters and the maximum Von Mises stress of pipeline is obtained,and the order of influence degree of parameters on the results is obtained.The relative deformation rate and the minimum curvature radius are used to represent the pipeline deformation.Taking yield strength as failure criterion,the ultimate load-bearing capacity of pipeline under ground subsidence and its variation with parameters are analyzed immediately.(3)The finite element model of notched polyethylene pipeline was established to study the variation of pipeline mechanical properties caused by the defect.Considering the variation of the maximum Von Mises stress of pipelines under different parameters,the quantitative relationship between them and the order of the influence degree of parameters are obtained.Ultimately,the variation law of the ultimate load-bearing capacity of pipelines with notches under settlement is conducted.(4)Based on the simulation results of specimen tensile test with crack,the finite element model of buried polyethylene pipeline with crack under land subsidence is established.The influence of ground subsidence on crack behavior of polyethylene pipeline is analyzed,and the variation rules of fracture characteristics and ultimate load-bearing capacity of pipeline under different parameters are obtained.(5)Based on the finite element model of buried polyethylene pipeline under ground subsidence,the burst pressure of the polyethylene pipeline under different parameters is calculated.When the pipeline is suffering from the ultimate displacement,the internal pressure of pipeline is regarded as the burst pressure.The damage model of buried polyethylene pipeline under ground subsidence based on burst pressure is established by using the unified theoretical damage model,and the damage of polyethylene pipeline under different parameters is analyzed.