Study On Deformation And Failure Criterion And Susceptible Zones For Buried Pipelines Across Landslides

Landslide is the most common geological disaster which threatens the safety of oil and gas pipelines.The safety state of pipelines across landslides is one of the hot and difficult problems in geoengineering scientific research.Therefore,based on correlation between pipeline deformation and failure and the characteristics of landslides under different conditions,exploring the law of pipeline deformation and failure across landslides and establishing the deformation and failure criterion for buried pipelines are not only of significant scientific significance in the study of interaction between pipeline and landslide,but also of important practical value in guiding the design of planned pipeline,the safety assessment and the safety protection of pipeline in service.In order to study the law of pipeline deformation and failure and determine the deformation and failure criterion for buried pipelines under the landslide action,the First and Second West-East Gas Pipeline in loess plateau area,as well as zhongwei-guiyang gas pipeline are taken as research areas.Based on correlation between pipeline deformation and failure and the characteristics of the landslide in research areas,this thesis first constructs the landslide and pipeline models,and then analyses stress and strain distribution characteristics with fully coupled numerical simulation method and non-fully coupled one respectively.Finally,the deformation and failure criterion for linear pipeline across different types of landslides and susceptible zones for polygonal-shape pipeline are determined,which are verified by typical cases.The numerical simulation results based on transverse landslides show that the stress concentration of pipeline is near the axis and both sides of the slip mass.The pipeline stress is positively correlated with landslide displacement,diameter thickness ratio and internal pressure,and negatively correlated with landslide width.The pipeline stress is the most sensitive to landslide displacement,then to pipe diameter-thickness ratio and internal pressure,and the least sensitive to landslide width.For the First and Second West-East Gas Pipeline under the most unfavorable wall thickness(14.6 mm,15.3 mm)and internal pressure(8MPa),the deformation and failure criterion under different landslide width or landslide displacement are got.Based on the response characteristics of pipeline stress and the principle of dimensional analysis,the prediction formula of pipeline maximum stress is proposed.The verification results of typical cases show that evaluation result based on the criterion is in good agreement with the actual situation.The numerical simulation results based on longitudinal landslides show that the stress concentration of the pipeline is at the top and the foot of the slope.Among the four main factors of landslide displacement,landslide length,pipe diameter-thickness ratio and internal pressure,when any three factors are fixed,the pipeline stress is positively correlated with another factor.The maximum tensile stress and maximum compressive stress are both most sensitive to landslide displacement.For the First and Second West-East Gas Pipeline under the most unfavorable wall thickness(14.6 mm,15.3 mm)and internal pressure(8MPa),the deformation and failure criterion under different landslide length or landslide displacement are got.Based on the response characteristics of pipeline stress and the principle of dimensional analysis,the prediction formula of pipeline maximum stress is proposed.The verification results of the typical case show that evaluation result based on the criterion is in good agreement with the actual situation.The numerical simulation of stress and strain in K1224 landslide show that the pipeline displacement of three directions is basically synchronous with landslide;the stress near the turning point of the pipeline is obviously greater than that of the straight pipeline section.The pipeline turning point and its adjacent segment are more sensitive and more prone to stress concentration,which is the key area of pipeline safety evaluation and prevention.Field monitoring data and local exposed pipeline status confirm the numerical simulation results.