Numerical Simulation Of Buried Pipeline In Collapsible Loess Area

The central and western regions of China are rich in oil and gas resources.In order to achieve a balanced supply and demand of oil and gas resources across the country,a long-distance pipeline route showing a trend from west to east came into being.The geological conditions in the northwest region are complex and the loess coverage rate is extremely high,which causes the pipelines along the route to inevitably pass through a large span of loess areas in the northwest region,especially the collapsible loess is a representative soil that is prone to self-wetting subsidence after soaking.The intensity will be greatly reduced,which will cause geological disasters such as subsidence,landslides and subsidence along the way to threaten the safe operation of buried pipelines.In order to study the stability of buried pipelines in collapsible loess regions,this paper uses a finite element method to analyze the displacement and stress of different pipe outer diameters and pipe wall thicknesses during collapsing.Using the eigenvalue buckling theory,the limit length of the buried pipeline in a loess disaster under certain conditions is obtained.The results show that: increasing the outer diameter and wall thickness of the pipeline and reducing the buried depth of the pipeline in the loess can effectively reduce the displacement of the pipeline in the collapsible loess,and the effect of the internal pressure on the maximum displacement of the pipeline is almost zero;Increasing the diameter and wall thickness can also effectively avoid the phenomenon of excessive local stress in the pipeline;the maximum stress and strain of the pipeline appear in the center of the wet zone,about 3/40 of the length of the pipeline and the positions of the fixed ends on both sides;The theoretical analysis of the buckling eigenvalues shows that the limit length of the collapse zone of the pipeline when the soil body is collapsing by weight is about 65m.Increasing the outer diameter and wall thickness of the pipeline can enhance the anti-buckling ability of buried pipelines when the loess is collapsing with water.Aiming at the situation of displacement load caused by soil subsidence on buried pipelines,the traditional stress-based design method and strain-based design method were compared,and the boundary conditions and load effects of buried pipelines were fully considered to determine the buried area in collapsible loess areas.Critical limit state and allowable strain of ground pipeline;Quantitative analysis of the influence of pipe outer diameter,pipe wall thickness and buried depth on the maximum axial tensile strain;Allowable axial tensile strain is used as the criterion for judging the failure of the pipeline,combined with Ramberg-Osgood constitutive model,the effective working length based on the strain design method is 87.8% higher than that based on the stress design method.