Study On Seismic Performance Of X80 Buried Pipeline Crossing Oblique-Reverse Fault

Into the 21 st century,China’s economic and social development speed and urbanization process gradually accelerated,followed by the increasing demand for energy,especially oil and natural gas.In order to meet the needs of social development and people’s production and life,the government timely launched the ‘West-East Gas Transmission’ project to promote the adjustment of China’s energy structure and industrial structure,and build a perfect energy supply system.Lots of research show that the fault dislocation caused by earthquake is particularly harmful to buried pipelines,which will cause excessive deformation of pipelines and lead to failure and failure.Therefore,the seismic response analysis and seismic safety design of buried pipeline across faults are of great significance.In this paper,the strain development and seismic performance of X80 buried pipeline under oblique-reverse fault movement are studied with the nonlinear finite element analysis method,as the background of the Fourth West-East Gas Pipeline Project.The main research contents and conclusions are as follows:1.A 3-D numerical model of buried X80 steel pipeline crossing oblique-reverse fault with considering the existence of trench backfill and underlying rock stratum in soil model is established using ABAQUS finite element analysis software.In view of the nonlinear problem in the process of fault movement,the coupling of shell element,equivalent boundary soil spring,solid element and nonlinear contact model is adopted as modeling method.According to the empirical statistical of engineering design ground motion in China,the relationship between fault displacement and earthquake magnitude is given.And the geometric dimension of pipeline trench is deduced based on the currently effective construction codes and rules.2.According to the parameters of the Fourth West-East Gas Pipeline Project,the strain development and deformation features of pipeline for local buckling and tensile fracture are obtained.The influence of various trench design parameters(pipeline burial depth,trench slope inclination,backfill soil type and thickness)on the failure process is discussed.Meanwhile,based on the failure criteria of buried pipelines,the critical fault displacements corresponding to different trench design schemes are studied.It was shown that the failure of pipelines can be delayed or even avoided by reasonable trench design in relatively weak seismic areas.Finally,the optimal scheme is further given to improve the seismic performance of pipeline,which provides a reference for the aseismatic design of buried pipelines at oblique-reverse fault crossings.3.Based on the concept of ‘Rigid Domain’,a protective devices is presented to improve the seismic performance of X80 buried pipeline under oblique-reverse fault dislocation.The influence of scope of protection on the strain development and regularities of distribution is studied by Numerical model analysis,the appropriate length of protective pipeline is proposed.The numerical analysis results show that,when the length of the protective pipeline is small,the peak position of the compressive strain of the buried pipeline appears outside the protected range,where the strain mutation occurs and develop rapidly,the local buckling failure process is even earlier than the unprotected pipeline.With the increase of protected range,the mutation phenomenon is weakened and the strain distribution tends to be stable.The improved finite element model was used to carry out parameter analysis of trench design factors to verify the seismic performance improvement effect of the protective device on the pipeline in the fault area.