Performance assessment of buried pipelines considering soil-structure interaction

埋地管道作为一种经济的输送液体和气体的手段被广泛使用。在加拿大和世界范围内，管道故障每年都会发生，造成重大的经济和环境后果。导致管道失效的因素包括由制造商缺陷引起的局部缺陷、施工/运行过程中的凹痕和腐蚀；以及操作/环境负载。管道的结构破坏通常由局部开始，并通过与周围土体的相互作用逐渐或灾难性地扩展，这取决于裂纹的扩展行为。本研究分别针对市政铸铁水管和钢制能源管道，研究了土-管相互作用，以评估由于局部缺陷和管道上的地面荷载引起的管壁结构破坏的发生和扩展。对于结构失效评估，将发展有限元建模技术，利用断裂力学来模拟管壁中的裂纹扩展。裂缝的起始点将通过在管道上创建不同形状的小缺陷和/或通过在回填体中使用空隙和/或在层理中施加模拟尖锐物体（岩石碎片）的集中力来增加局部应力集中来定义。用于分析的管道材料特性（即弹性参数、应变率相关的应力-应变关系和断裂韧性）将使用从管道样品中提取的样品进行实验室测试来确定。为了模拟轴向拔出过程中的地面荷载，将对管道周围土壤进行有限元建模，模拟大变形和应变局部化。土的应力应变行为将通过开发新的本构模型来模拟，这些模型捕获了峰前硬化、峰后软化、相对密度和围压依赖于砂的行为。对于本构模型的开发，将进行实验室测试，特别注意低应力水平下的土壤行为，因为管道周围的应力通常低于典型岩土工程问题的预期应力。本研究对管道破坏机制和载荷的理解可用于开发新的管道设计指南。本研究结果将有助于合理设计市政和能源管道，从而最大限度地减少管道故障。两名博士，三名硕士和两名本科生将通过拟议的NSERC发现基金获得资助。

Buried pipelines are widely used as an economic means of transporting liquid and gas. Pipeline failure occurs every year in Canada and worldwide resulting in significant economic and environmental consequences. Factors contributing to pipeline failure include local defects resulting from manufacturer imperfection, dents during construction/operation, and corrosion; and operational/environmental loads. Structural failure of the pipe often initiates locally and propagates gradually or catastrophically, depending upon crack propagation behaviour, through interaction with surrounding soil. This research investigates soil-pipe interaction for the assessments of the structural failure initiation and propagation in a pipe wall due to local defects and the ground loads on pipelines, for municipal cast iron water mains and steel energy pipelines, respectively. For structural failure assessment, finite element modeling techniques will be developed to model crack propagation in the pipe wall using fracture mechanics. The point of initiation of a crack will be defined by creating small defects of different shapes on the pipe and/or by increasing stress concentration locally using a void in the backfill and/or applying concentrated forces simulating sharp objects (rock pieces) in the bedding. Pipe material properties (i.e., elastic parameters, strain-rate dependent stress-strain relations and fracture toughness) for the analysis will be determined using laboratory tests with specimens extracted from pipe samples. For modeling the ground load during axial pullout, finite element modeling will be performed with simulation of large deformation and strain localizations in the soil surrounding the pipeline. The stressstrain behaviour of soil will be modeled through development of new constitutive models capturing the pre-peak hardening, post-peak softening, relative density and confining pressure dependent behaviour of sand. For the constitutive model development, laboratory tests will be conducted with particular attention to the soil behaviour at a low stress level, because the stress around the pipelines is generally lower than the expected stress in typical geotechnical problems.The understanding of the failure mechanisms and the loads from this research can be used to develop novel design guidelines for the pipelines. Outcomes of this research will thus contribute towards rational design of municipal and energy pipelines and thus to the minimization of pipeline failure. Two doctoral, three Masters and two undergraduate students will be supported through the proposed NSERC Discovery grant.