Dynamic Response Analysis Of Buried Pipelines Containing Corrosion Under The Impact Of Falling Rocks

China’s vast territory,geological conditions are complex and variable,and the longdistance pipeline covers a wide area,so it is difficult to avoid crossing geological disaster areas during the pipeline design process.Rockfall disaster occurrence conditions are influenced by natural environment and human factors,with uncertainty and unpredictable characteristics.When the pipeline crosses the collapse and rockfall geological hazard area,the sudden collapse and rockfall is one of the main geological hazards leading to the failure and damage of the long-distance pipeline,which poses a great threat to the safety of the long-distance pipeline.In addition,it is difficult to avoid corrosion problems in the pipeline during transmission operation,so the risk of pipeline failure and damage due to corrosion defects also increases.In the collapse of rockfall and other disaster loads,pipeline corrosion defects will further exacerbate the risk of pipeline failure.At present,most scholars have studied the impact of rockfall hazards and corrosion defects on pipelines respectively,and few scholars have conducted studies on the dynamic response of corroded pipelines under rockfall impact.In this paper,we investigate a variety of factors affecting the dynamic response of buried pipelines impacted by falling rocks,and propose countermeasures and recommendations to provide a scientific basis for ensuring the safe transmission of long-distance pipelines under the collapse and rockfall area:(1)Investigate the current situation of domestic and foreign research,summarize and summarize the theoretical basis and mechanical model related to rockfall impact buried pipeline.Determine the material model and parameters of rockfall,soil and pipeline,set the mutual contact between pipe and soil,boundary conditions and load settings,and construct the finite element model of complete buried pipeline under the action of rockfall impact.The test data and simulation results are compared to effectively verify the reliability of the finite element model.(2)Based on the finite element model of the complete buried pipeline under the impact of falling rocks,the mechanical changes of the influencing factors of the internal pressure of the complete pipeline,the impact velocity of falling rocks,the volume of falling rocks,the burial depth of the pipeline and the wall thickness of the pipeline are analyzed.The study shows that the influence of the internal pressure on the stress and strain of the pipe is obvious,and the stress and strain of the pipe increases linearly with the increase of the conveying pressure.With the increase of rockfall impact speed,the higher the pressure,the more likely the pipeline yield damage.The thickening of the cladding layer can effectively reduce the impact load of falling rocks and delay the impact time.Therefore,it is reasonable to consider setting the burial depth of the pipe below2.1m in the collapsed rockfall area.The wall thickness of the pipeline is increased to effectively improve the ability of the pipeline to resist impact loads,and the optimal pipeline wall thickness is selected in consideration of the economy and safety of the pipeline construction.(3)Selected uniform wall thickness defects as the shape of the pipeline corrosion defects,due to different pipeline corrosion defect size is not uniform,so the introduction of dimensionless parameters of the pipeline corrosion defect size parameters to simplify the establishment of corrosion defects pipeline local thinning model.(4)By changing the corrosion defect parameters of the corroded pipe,the dynamic response of the corroded buried pipe under the action of falling stone impact is analyzed.At the same time,the internal pressure of the pipe,the impact velocity of the falling stone,the volume of the falling stone,the burial depth of the pipe and the wall thickness of the pipe are studied to compare and analyze the mechanical change law of the corroded pipe and the intact pipe.Research shows that: when the pipeline corrosion situation,corrosion defects in the region will appear stress concentration phenomenon,resulting in the pipeline is more likely to enter the plastic stage and lead to pipe failure.When the corrosion depth μ more than 40%,the maximum strain of the pipeline approximation exponential increase,corrosion depth deepening of the pipeline mechanics is extremely obvious.When the corrosion length of the order of magnitude n more than 10,the internal pressure of the lower corrosion of the maximum stress strain of the pipe gradually stabilized,while the internal pressure of the higher corrosion of the pipe strain is still growing with the corrosion length and become larger.When the pipe corrosion width angle θ more than 20 °,the peak stress strain of the pipe are stabilized.From the overall magnitude of change,the corrosion defect width on the pipe stress strain effect is not obvious.The combination of pipeline pressure and impact load increases the risk of failure of corrosion-defective pipelines,resulting in a buried pipeline under the action of falling stone impact is more prone to failure damage.Increase corrosion pipe burial depth and wall thickness can effectively reduce the impact load of falling stone,to protect the corrosion of the pipeline operation safety.(5)Analysis of the sensitivity factors of corrosion pipeline under the effect of rockfall disaster,the study shows that: with the internal pressure of the pipe,rockfall impact velocity,rockfall volume,corrosion defect depth,corrosion defect length increase showing a positive impact relationship,and corrosion width angle,burial depth,pipe wall thickness increase on the pipeline stress,strain peak shows an inverse impact relationship.Comprehensive derived from the order of sensitivity of each factor: rockfall impact velocity > pipeline burial depth > corrosion depth > pipeline wall thickness > pipeline internal pressure > rockfall volume > corrosion length > corrosion width;(6)From the rockfall protection and pipeline protection two aspects,the collapse of rockfall area pipeline protection management.Rockfall protection,through the removal of dangerous rocks,anchoring dangerous rocks and stabilization of the collapse surface and other measures to manage rockfall protection;pipeline protection,consider the pipeline design route when the pipeline is locally adjusted away from the collapse of rockfall area.At the same time,the safe operation of long-distance pipelines can be effectively ensured through measures such as increasing the burial depth of pipelines,adopting larger wall thickness pipelines,selecting corrosion-resistant pipeline materials and advanced anti-corrosion coatings,and timely monitoring the corrosion of buried pipelines.