Strain Analysis Of Buried Oil And Gas Pipelines In Mine Subsidence Areas

Mine subsidence is one of the typically geological hazard threats for long distance oil and gas pipeline.Many pipelines cross regions with completed and ongoing underground mining activities,such as the second China West-to-East pipeline.Pipelines in subsidence areas will be under complex load conditions containing bending,tension or compression due to the ground deformation,in the potential of leading to rupture or local buckling failure.Thus,accurate strain prediction of pipelines in mine subsidence areas has a great significance for pipeline safety.Based on the Probability Function Integration Method,the influences of the effect factors on the ground displacements in the subsidence areas have been conducted,and the trends of soil displacements have been derived.Based on the derived ground displacement results,a refined finite element model of buried pipeline crossing subsidence areas was established,in which the pipe was simulated by the non-linear shell element and the pipe soil interaction relationship was simulated by non-linear spring element.Both large deformation and material nonlinearity were considered in the numerical model.Based on the FEM,parametric study was conducted to investigate the influences of the effect factors on the pipe strain.Results show that,when the pipeline is subjected to continue ground subsidence load,vertical displacement of pipeline is consistent with ground deformation,bending strain in the pipe is smaller than axial strain,the maximum compressive strain occurs in the middle of the subsidence area,and the maximum tensile strain shows in the edge of the subsidence area.Axial strain of the pipeline in the subsidence area increases with the increase of overlying strata stiffness,strike length and mining depth.But the mining thickness has negligible effect on the axial strain.The increase of internal pressure,buried depth and pipe soil ineteraction reduction factor will increase the axial strain.While a larger thickness will induce a smaller axial strain.Based on bilinear material model,an analytic calculation method of pipeline in subsidence area was developed considering the pipe-soil interaction and large geometric deformation.A calculation program was also provided by general software MATLAB to solve the problem.The applicability and the accuracy of the proposed method were validated by comparing with the finite element results.Finally,based on the strain limit criteria,the design and assessment method for pipelines in subsidence areas were provided.And a comprehensive assessment system based on C # programming language and commercial FEM software ABAQUS was developed.