The Safety Of Buried Oil-Gas Pipeline Under Geological Disaster

The oil and gas pipelines such as the West-East pipeline and the Sichuan-East pipeline are located in the the Western Region of China with complex geological environmet, which leads to recurrent multiple geohazards. So it is important to study the safety of buried oil-gas pipeline under geo-disaster. The influence of landslip, active fault and earthquake wave on the safety of pipeline, including corresponding mechanical responses in buried pipeline and it's engineering technology were discussed in this thesis. The detailed works include:1. The stability of Luo Zhentian slope was studied fore and after trenching excavation, and proposed its scheme to avoid landslide. The FEM model of buried pipeline and landslide was constructed to simulate the dynamic response of pipe caused by mountain landslide. The whole process can be roughly divided into two strategic periods. Firstly, rockfall slided and washed the covered soil of pipeline, secondly, rockfall flushed the pipeline directly. The pipeline remained steady in the first stage, while it suffered buckling in the second stage. Some main influential factors, such as the landslide length, the landslide angle, the volume of rockfall, the style of backfill, the burying depth of pipeline, were studied,. The results indicated that pipe was destroyed when landslide length and landslide angle was small. The volume of rockfall was another important factor that control the maximum of stress in pipeline. The large burying depth of pipeline could decrease the impact of loading, thus a small deformation was caused in buried pipeline with sand backfill.2. Current beam theory and design methods for buried pipeline crossing an active fault couldn't be used to analyze the large deformation in the pipe section, such as bucklling. Therefore a coupled pipeling-soil model, combined by cylindrical shell element with nonlinear spring, was suggested in this paper. The large nonlinear deformation of a buried pipeline under fault movement is simulated by ANSYS software. Some influential factors on the seismic responses of buried pipeline were studied. The best angles between pipeline and fault is 900, the small burying depth of pipeline is better, the large diameter of pipeline and the high ratio of diameter to thickness of pipe can help it to resistant to large fault movement.3. Furthermore, a non-linear contact element was incorporated into the forenamed coupled pipeline-soil, to study the mechanical behavior of buried pipeline under the latitudinal earthquake wave recorded in Tianjin 1946. The stress in pipeline increases with increasing earthquake wave amplitude, burying depth, and the friction angle between pipe and soil.