| With the large number of natural gas pipeline laying,third-party load(rock impact,ramming,traffic load)on the buried pipeline interference is increasingly serious,especially the collapse caused by rockfall disaster.Rockfall has a greater impact energy,the impact of the damage can easily exceed the ultimate load capacity of the pipeline,large diameter high grade steel pipe belongs to the shell structure,damage is more serious.However,the study of the limit state design method of large diameter and high grade steel pipe under the impact force of rock falling is currently lacking.In this paper,the whole process of rockfall from the slope movement to the impact pipeline is studied by means of impact theory,finite element numerical simulation and probability analysis method.It is concluded that the X80 steel-grade buried pipeline with different wall thickness Stress distribution law and design methods,the main results are as follows:(1)The theoretical analysis of the rock-rock slope movement process and the rock-impact process shows that the slope height,slope and rock weight are the main factors influencing the impact force of the rockfall,and the influence factors for the rock impact are established for the main influencing factors Regular 100 slope models.Based on the stress failure criterion,the pipeline limit state design method is studied to determine the limit state of the pipeline as the ultimate limit state(ULS).(2)Based on the rockfall slope model established by RocFall software,the normal distribution of the impact velocity,impact angle and impact position during the first impact of the rockfall slope movement is obtained.Based on the improved Ye Si qiao empirical formula,the impact force of rockfall was calculated,and the impact force of the rockfall was obeyed by Gamma by SPSS software.The shape parameter was 5.050 and the rate parameter was 0.002.Sensitivity analysis of the main factors influencing the impact of rockfall was carried out.The sensitivity of the influencing factors was as follows:the height of the rockfall>slope gradient>rockfall weight.(3)Simulation and analysis of different impact schemes based on ABAQUS finite element software are carried out.It is found that the maximum stress of the pipe is at the top of the pipe under the impact force.The maximum stress at the top of the pipe is analyzed statistically by using the SPSS statistical software for ?1219×18.4mm,?1219×22mm and?1219 × 26.4 mm under different depths.The maximum stress at the top of the pipeline is subject to the Gamma distribution.Through the Matlab programming,the stress distribution of the pipeline is fitted,and a total of 12 sets of Gamma distribution probability density function parameters are determined.(4)Through the Matlab programming,the direct sampling Monte Carlo method is used to calculate the pipeline failure probability and reliability index.The critical buried depths of X80 steel pipes with different specifications of ?1219×18.4 mm,?1219×22 mm and?1219×26.4mm were studied.The critical buried depths of the pipes were 1.33 m,1.26 m and 1.15 m,respectively.The pipe stress limits do not exceed the minimum strength values specified in the API SPEC 5L "Pipeline Specifications" at the target safety level.Based on the limit state equation Z = 0.9?s-?von mises for pipe limit state design,and the limit state design expression of X80 grade buried pipeline under different target safety level is given.The design method of limit state of X80 buried pipeline is put forward and the limit state design process.Based on the method of probability analysis,the design method and design parameters of the pipeline limit state not only improve the reliability of the reliability analysis of the buried gas pipeline,but also have the risk assessment,pipeline design and construction of the X80 grade buried pipeline in the collapse zone significance. |
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