| Landslides caused by precipitation and earthquakes are important reasons for the failure of long oil and gas pipelines.At the same time,long pipeline is an important part of modern economic construction.Therefore,it is of great significance to study the safety and reliability of pipelines under landslide and Seismic Landslides.On the basis of previous studies,the effects of landslides and Seismic Landslides on high strength and large diameter pipelines are studied,and the factors that affect the safe operation of the pipeline system are discussed in this paper.The main work of this paper are as follows:First of all,the mechanical analysis of two typical laying pipelines is carried out,and the formulas for calculating vertical and lateral earth pressures of pipelines are given.Comparing the merits and demerits of typical Pipe-soil interaction model at present,and the finite element model of soil springs is chosen as the mechanical model of this paper.What's more,the design criterion based on strain is selected in this paper by analyzing the advantages of it.Based on the analysis of the strain design criteria at home and abroad,the domestic Seismic Technical Code for Oil and Gas Transmission Pipeline Engineering(GB50470-2017)is selected as the strain calculation method in this paper,and the allowable strain values of the corresponding pipes are given through an example.In this paper,a numerical model has been established using the FEM software.Through it,the axial strain and lateral displacement of pipeline under landslide impact are calculated,and then the difference of the pipeline's landslide strain resistance between pipeline with internal pressure and without internal pressure is analyzed.What's more,the influence of soil displacement,soil friction angle and pipeline steel grade on the axial strain of pipeline under landslide is analyzed.The results show that the maximum axial strain of the pipeline occurs at the middle position of the landslide section,and the displacement of the slide soil position during the landslide is the most important factor affecting the safety of the pipeline.Secondly,adding earthquake waves on the former model to analyze the response state of pipeline under the earthquake landslide.Then the axial strain law of pipeline under the action of earthquake landslide is obtained.By comparing with the strain results of the pipeline mentioned above,the influence of earthquake on the internal pressure and steel grade of the pipeline is analyzed.The results show that the earthquake obviously increases the strain of the pipe,and it has the most obvious effect on the friction angle in the soil,followed by the buried depth of the pipeline,the displacement of the soil and the internal pressure of the pipe.In addition,the reliability of buried pipeline under the impact of earthquake landslide is calculated by Monte-Carlo method.Then the relation formula of reliability and reliability of pipeline is given after statistical analysis,and the reliability of pipeline under different confidence level is calculated.Then the sensitivity analysis of the factors influencing the pipeline reliability is carried out.The results show that landslide displacement,internal friction angle,outer diameter,depth,wall thickness and elastic modulus are significant factors affecting pipeline reliability.Finally,the Bayesian network and the fault tree model are combined to evaluate the safety of oil and gas pipeline under normal operation,and the importance order of the basic events is obtained.The results show that the main factors leading to pipeline failure are human's unsafe behavior,natural disasters and pipeline corrosion.Based on the analysis results of the two methods,it is suggested that the pipeline arrangement should avoid earthquake and landslide prone areas as far as possible,and try to choose the large-diameter,thick-walled steel pipe shallow buried in the soil with small internal friction angle to increase the safety of the pipeline. |
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