地震波作用下埋地管道的应变积累破坏机制研究

Buried pipelines constitute a key component of critical lifeline systems, such as water supply, gas supply and sewer disposal et al. Soil-structure interaction analysis of wave propagation effects on buried pipelines has practical significance on aseismic design of lifeline systems. Current seismic design guidelines typically assume soils and pipelines as linear elastic structures. This assumption is overly simplified and is difficult to simulate the actual process of soil-structure interaction. This research develops soil-structure interaction models for pipeline damage analysis due to seismic wave propagation effects using strain accumulation method. With the assumption that soil is elasto-plastic material, a criterion is developed for determining the occurrence of relative slippage between soil and pipeline. An analytical model is developed for estimating strains in pipelines when the relative slippage occurs. For buried segmented pipelines, with the consideration of pipeline structural non-linearity, the strain redistribution around the joint is analyzed and the joint damage is assessed using analytical methods. For continuous welded steel pipelines, the mechanism of fatigue fracture is explored by analyzing the strain accumulation during ultralow cycle, large strain earthquake loads. The mechanical process from local buckling to fatigue fracturing at the welded joint is investigated. The models developed in this research are verified using numerical simulations, laboratory tests, and field artificial blasting test, and are calibrated with case history pipeline damage scenarios. The research aims to explore the damage mechanism of buried pipes and develop models for pipeline damage assessment. Findings from this research can be beneficial to the aseismic theory and design practices of buried pipelines.

埋地管道的地震破坏机制研究是提高供水、供气、污水处理等生命线管道抗震设计的前提。目前，埋地管道抗震设计一般假定土体和管道是线弹性材料，难以反映土-结相互作用。埋地管道的地震破坏是在地震波作用下管道产生应变的积累，进而在接头或管体薄弱处发生破坏的过程。本项目拟通过考虑土体的弹塑性和管道的结构非线性，采用应变分析法，研究：①地震波作用下，土-结相互作用产生的管道内的应变分布，建立判别管-土能否共同变形的准则和求解管道内应变的模型；②分节管道由于管道结构非线性产生的管道内应变分布的非一致性，以及引起的管道接头处的拉伸或压缩破坏；③连续焊接钢管焊接区管体在超低周期、大应变地震荷载作用下由局部屈曲发展成疲劳开裂的破坏过程。预期所建立的模型将通过数值模拟、室内试验、现场爆破试验和历史震害加以考核和验证。本研究拟建立基于应变积累的、有效的管道破坏分析模型，为提升管道抗震理论和设计水平奠定一定的理论基础。

本项目以供水、供气、污水等生命线管道以及盾构隧道、海底隧道等线性管道为研究对象，研究管道在地震波作用下的土-结相互作用及由此产生的结构响应和破坏。主要研究内容和结果包括：1）研究了地震波作用下土-结相互作用产生的管道应变，建立了管-土能否共同变形的判别准则及管道应变计算的数学模型。研究表明：在地震波的作用下，考虑土体的弹塑性，当f/EAR≥1（其中：f为管-土交界面剪力弹性极限；E为管材杨氏模量；A为管道截面面积；R=4Vap/λCa，Vap为沿管道轴向的地面粒子速度峰值，λ为波长，Ca为沿管道轴向的视波速），管土共同变形，管应变处处等于地应变；当f/EAR<1，管应变处处小于地应变，管应变为地应变与f/EAR的乘积；有限元模拟和现场爆炸试验验证了判别准则和计算模型的正确性。2）研究了分节管道脆性和延性接头的荷载-变形关系，建立了不同特性接头在地震波作用下变形的解析和有限元模型。脆性接头的变形主要由接头的开裂应变极限决定；柔性接头的变形主要取决于接头的相对强度，变形在强度较弱的接头处集中，变形量和漏水概率随接头强度的相对降低而线性增加；有限元模拟与地震实例观测的接头变形量和漏水概率与解析模型结果接近。3）研究了连续焊接钢管焊接区管体的荷载-变形关系，建立了地震波作用下管体局部屈曲及疲劳开裂的数学模型。研究表明：焊接区管体的轴向强度随管体变形先增大，然后线性下降，最后趋于稳定；在地震波作用下，如焊接区管体轴向压缩卸载速率小于土体卸载速率，则管体稳定压缩；反之，则管体失稳，发生局部屈曲，然后管体在超低周期、大应变地震荷载作用下随着材料晶粒间空洞的逐步扩张而发生开裂；对比1985年墨西哥地震历史震害数据发现，考虑非对称荷载的改进循环空洞扩张模型（CVGM）能较好地预测管体的开裂过程。本研究明确了地震波作用下的管道与土体的相互作用机理，建立了管道应变、接头变形、焊接区管体局部屈曲和开裂的数学模型，研究结论具有较强的科学意义和应用价值。