Mechanical Properties Test And Finite Element Analysis Of Buried Pipelines Crossing Faults

As an important part of the urban infrastructures and the most efficient,economical and reliable transportation way of oil and natural gas,buried steel pipelines are called as the underground urban lifelines and the lifelines of oil and gas fields.With the development of urbanization and exploitation of oil and gas resources in China,the construction of buried steel pipelines increases day by day,and the structural integrity and reliability are paid more and more attention in practice.China is a vast country with frequent earthquakes.Damages and ruptures of buried pipelines will directly lead to service interruption of important urban infrastructure and leakage accidents of oil and gas,and even cause fire and explosion,it has a serious impact on the relief during earthquakes,the reconstruction after earthquakes and the ecological environment.Fault movements are one of the main causes of seismic damage of buried pipelines.In order to avoid such accidents,it is necessary to accurately study the mechanical properties of buried pipelines across faults and evaluate their safety.In this paper,the mechanical properties of buried pipelines across faults are studied from three aspects: theory method,finite element analysis and experiment research and combined with an engineering example,The main research work and results are as follows:(1)The spring is selected to replace the small deformation section of pipeline-soil,the relationship between pipeline axial force and relative displacement of pipe-soil is established with consideration of the interaction of pipeline-soil,Based on the elastic foundation beam theory,the equilibrium equation of pipeline force and the compatibility equation of deformation,the analytical method of strain and deformation of buried pipeline across faults is obtained.Based on the principle of similarity of gravity,cross-section shear force and inertia force of pipeline,the similarity ratio of model test is determined to be 1:15.(2)A test device is designed and manufactured to study the action mechanism of various types of faults on buried pipelines.Fourteen buried pipelines are tested by simulating fault movements.The strain distribution and vertical deformation characteristics of buried pipelines under fault movements are obtained.In addition,the effects of fault movements,pipe diameter,buried depth,soil type,spring elasticity coefficient and pipeline angle crossing faults on the mechanical properties of buried pipelines are studied.(3)The finite element model of buried pipeline across faults is established.By comparing the Mises values of the equivalent spring boundary shell model with thatof the fixed boundary shell model,it is proved that the spring device can be used for finite element analysis and model test.On this basis,the influence of different types of faults on the pipeline is discussed,and the strain nephogram along the axis of the pipeline and Mises stress curve are obtained.(4)The criteria and methods for safety assessment of buried pipelines across faults are introduced and illustrated by engineering examples.The theoretical analysis method in this paper,the finite element method with equivalent spring,the finite element method with fixed boundary and the theoretical method adopted in the code(GB/T 50470-2017)are compared and analyzed.At the end,the safety guarantee measures for buried pipelines across faults are put forward.