Seismic Response Analysis Of Buried Oil And Gas Pipelines Crossing Active Fault

With the growth of energy demand,China has implemented the Central Asia Gas Pipeline Project in order to meet the energy needs and national strategic development needs.The project area is a high intensity seismic region.The seismic activity is frequent,the geological tectonic fracture activity is high-occurrence,and the construction is difficult.The existing study of buried pipeline crossing active faults is mainly about single fault,lacks of research on complex fault.The majority study doesn't consider all kinds of nonlinear factors,is mainly based on the stress analysis about the seismic response of buried pipeline,lacks of research on strain.At the same time,most study lacks of the research on pipeline under the action of working loads and earthquake loads,and it is not close to engineering practice enough.Therefore,it is of great significance to study the seismic response of buried pipelines crossing active faults.In this paper,the characteristics and classification of active faults were summarized.And the response analysis methods of buried pipeline under the action of fault and seismic wave were summarized.Then with the actual working conditions as research background,using the nonlinear numerical analysis method,this paper analyzed the stress and strain of buried pipelines under the action of fault movement,especially the oblique slip fault,and summarized the influence of various conditions on pipeline axial strain.At the same time,the dynamic response of buried pipeline under the action of seismic wave was analyzed.Then this paper analyzed the factors that influence the strain of the pipeline and analyzed pipeline axial strain under the joint action of fault movement and seismic wave.The conclusions are as follows:1.The fault movement has great influence on buried pipeline.Under the action of fault,buried pipeline warps with soil,it has the maximum tensile strain and compressive strain on one side of the fault.Under the action of oblique slip fault and single fault,the regularity of strain variation is consistent.The axial strain increases with the increase of fault movement,and compressive strain's growth rate is higher than tensile strain.The change trend of pipeline strain is more rapid under oblique slip fault.Different working conditions have different effects on pipeline strain.In the project,small dip and azimuth angle,shallow buried-soft soil,small diameter-thick wall and low pressure pipeline should be used for fortification.The regression formula of pipeline's axial strain under fault movement is proposed to provide certain guidance for the engineering strain design.2.The seismic wave has great influence on pipeline.Buried pipelines crossing faults under seismic waves have the maximum axial tensile strain and compressive strain,and the two points are in the same cross section.There is a certain distance between fault and the maximum strain points.With the increase of peak acceleration,pipeline axial strain increases.Under different conditions,pipeline axial strain's change rule is also different from fault movement.To adopt big dip and azimuth angle,shallow and hard soil,large diameter and thick wall,low pressure and other measures in project,can reduce the influence of seismic wave.3.There is a large axial strain increment in buried pipeline under the joint action of fault and seismic wave.Especially under small displacement and strong earthquake,the maximum axial tensile and compressive strain of buried pipelines can increase to 243.18% compared to only under fault movement.Pipeline dangerous point's outwards migration distance can reach 10 m under common action.When the fault displacement's component is less than 0.2m,the seismic wave should be taken as control factor,and measures should be taken to reduce the strain.In the case of fault displacement's component is greater than 0.2m,the fault movement is the main factor,in which earthquake effect can be ignored.