Study On Fault Analysis Method Of Cross - Fault Buried Gas Pipeline Fault

In recent years, the implementation of long distance natural gas pipeline project such as West-East gas transmission pipeline, Sichuan-East gas transmission pipeline, import liquefied natural gas (LNG) pipeline, as well as the construction of the transnational pipeline project of China-Central Asia and China-Myanmar, which diversifies the gas source in China, builds the main gas pipeline network. With widely distributed active faults, China is one of the countries hit most seriously by earthquake in the world. A lot of seismic damage data have demonstrated that the pipeline is usually damaged when crossing an active fault. Therefore, it’s necessary to carry on the aseismatic design and seismic safety evaluation to the existing pipelines so as to avoid or reduce the damage in the future earthquake. The research on response of the buried gas pipeline crossing fault under the fault movement is carried on in this thesis. The main research contents are as following:(1) The development course and present situation of the analysis method of the response of buried pipelines crossing fault to the fault rupture both at home and abroad are reviewed The feature and achivement of the existing methods including analytical method, finite element numerical simulating technology and test research are summarized, and the things which need to be improved and perfected are also pointed out.(2) Different elements of active faults and the damage mechanism of the pipeline under three kinds of fault movement are analyzed. The buried pipeline and the surrounding soils are taken out together from the semi infinite medium, and dissociated with SHELL281element and SOLID45element respectively. The pipeline is simulated as thin-walled hollow cylindrical structure and the soil is simulated as uniform entity medium.On the premise of ensuring the calculation accuracy, according to the actual condition, the pipeline-soil nonlinear contact model based on state nonlinear theory is established, which is used to simulated the slippage, separation and closure phenomenon between pipeline and soil. Boundary conditions are determined by analyzing the load-carrying mode of fault rupture displacement. The interaction between the pipeline and the surrounding soil was analyzed by using the finite element method to determine the effective calculation area of the model. Different constitutive models of pipeline and soil are compared, and then the trilinear material property model for pipeline and the Drucker-Prager model for soil are chosen. Through the preparation above, a three-dimension multiple nonlinear finite element numerical simulation model of buried gas pipeline crossing fault is put forward.(3) After the validation of the correctness and effectiveness of the finite element model, the deformation responses of the thin and hollow pipeline crossing faults to faults movement are explored. And the deformation law of the pipeline under different fault displacements is analyzed. Based on the stress and strain distribution along the pipeline axial, the potential damage location is determined, and the conclusion that the stress and strain distribution along the axial of the pipeline at the top and bottom is ant-symmetrical is also obtained. Based on the stress-strain response of the buried gas pipeline subjected to the fault rupture and the stress-strain cloud maps and the strain-displacement graphs, the effect of some factors, including wall thickness, pipeline diameter, burial depth, pipeline material, crossing angle, soil stiffness, the thickness of the fault rupture zone, as well as internal pressure, influencing on deformation response are analyzed systematically.(4) Based on the complementation and improving of the calculation steps of the classic analytical methods, combined with the analysis results of influence factors by the finite element model, a simplified calculating formula used to calculate the maximum strain of the gas pipeline was proposed, which can be used for engineering aseismatic design. The formula was validated by comparing the calculation results of the simplified formula with that of some other formulas such as Takada-Hassani formula which are from the published literature.(5) With the survey of pipeline seismic damage data, incorporating with the finite simulated results, the damage modes of the buried pipeline crossing faults are summarized. On this basis the influence factors analysis, the effective aseismic measures applied to the buried pipeline crossing faults and aseismic reform steps for in-service pipelines are put forward.