Seismic wave propagation effects on buried segmented pipelines

This paper deals with seismic wave propagation effects on buried segmented pipelines. A finite element model is developed for estimating the axial pipe strain and relative joint displacement of segmented pipelines. The model accounts for the effects of peak ground strain, shear transfer between soil and pipeline, axial stiffness of the pipeline, joint characteristics of the pipeline, and variability of the joint capacity and stiffness. For engineering applications, simplified analytical equations are developed for estimating the maximum pipe strain and relative joint displacement. The finite element and analytical solutions show that the segmented pipeline is relatively flexible with respect to ground deformation induced by seismic waves and deforms together with the ground. The ground strain within each pipe segmental length is shared by the joint displacement and pipe barrel strain. When the maximum ground strain is higher than 0.001, the pipe barrel strain is relatively small and can be ignored. The relative joint displacement of the segmented pipeline is mainly affected by the variability of the joint pullout capacity and accumulates at locally weak joints.     

Centrifuge modeling of buried continuous pipelines subjected to normal faulting

Seismic ground faulting is the greatest hazard for continuous buried pipelines.Over the years,researchers have attempted to understand pipeline behavior mostly via numerical modeling such as the finite element method.The lack of well-documented field case histories of pipeline failure from seismic ground faulting and the cost and complicated facilities needed for full-scale experimental simulation mean that a centrifuge-based method to determine the behavior of pipelines subjected to faulting is best to verify numerical approaches.This paper presents results from three centrifuge tests designed to investigate continuous buried steel pipeline behavior subjected to normal faulting.The experimental setup and procedure are described and the recorded axial and bending strains induced in a pipeline are presented and compared to those obtained via analytical methods.The influence of factors such as faulting offset,burial depth and pipe diameter on the axial and bending strains of pipes and on ground soil failure and pipeline deformation patterns are also investigated.Finally,the tensile rupture of a pipeline due to normal faulting is investigated.     

Numerical simulation and seismic performance evaluation of buried pipelines rehabilitated with cured‐in‐place‐pipe liner under seismic wave propagation

The cured‐in‐place‐pipe (CIPP) liner technology involves installation of flexible polymeric composite liners coated with thermosetting resin to the inner surfaces of existing buried pipelines. This innovative technology provides an efficient, economic, and environmentally friendly alternative for rehabilitation of structurally compromised underground pipelines without expensive and disruptive excavation. However, the lack of analytical/numerical procedures to quantify the seismic performance of CIPP liner reinforced pipelines remains a barrier to the seismic design and rehabilitation of underground pipelines. This paper first develops an experimentally validated hysteretic model of ductile iron push‐on joints, reinforced with one particular type of CIPP liner under repeated axial loading. A numerical procedure is then proposed to systematically assess the seismic performance and fragility of straight buried pipelines incorporating push‐on joints and subjected to transient ground deformations. The numerical results indicate that CIPP liner‐reinforced pipelines exhibit favorable robust seismic performance with limited joint damage under high‐intensity transient ground deformations. Copyright © 2016 John Wiley & Sons, Ltd.     

管土动力相互作用分析

相互作用问题是地下管线动力分析中的重点和难点。本文借助于大型有限元软件ABAQUS/Standard中的管土相互作用单元(Pipe-soil interaction element,简称PSI单元)并利用直剪试验实测的接触面本构关系,对管线与土体之间的相互作用进行了数值模拟研究,计算得到了地下管线在动力作用下的内力和变形。分析结果与试验结果的对比表明,本文方法具有良好的计算精度,对地下管线的分析和设计具有参考意义。     

Permanent earthquake‐induced actions in buried pipelines: Numerical modeling and experimental verification

Buried pipelines are often constructed in seismic and other geohazard areas, where severe ground deformations may induce severe strains in the pipeline. Calculation of those strains is essential for assessing pipeline integrity, and therefore, the development of efficient models accounting for soil‐pipe interaction is required. The present paper is aiming at developing efficient tools for calculating ground‐induced deformation on buried pipelines, often triggered by earthquake action, in the form of fault rupture, liquefaction‐induced lateral spreading, soil subsidence, or landslide. Soil‐pipe interaction is investigated by using advanced numerical tools, which employ solid elements for the soil, shell elements for the pipe, and account for soil‐pipe interaction, supported by large‐scale experiments. Soil‐pipe interaction in axial and transverse directions is evaluated first, using results from special‐purpose experiments and finite element simulations. The comparison between experimental and numerical results offers valuable information on key material parameters, necessary for accurate simulation of soil‐pipe interaction. Furthermore, reference is made to relevant provisions of design recommendations. Using the finite element models, calibrated from these experiments, pipeline performance at seismic‐fault crossings is analyzed, emphasizing on soil‐pipe interaction effects in the axial direction. The second part refers to full‐scale experiments, performed on a unique testing device. These experiments are modeled with the finite element tools to verify their efficiency in simulating soil‐pipe response under landslide or strike‐slip fault movement. The large‐scale experimental results compare very well with the numerical predictions, verifying the capability of the finite element models for accurate prediction of pipeline response under permanent earthquake‐induced ground deformations.     

场地沉陷埋地管道反应分析方法

场地的不均匀沉陷是导致埋地管线破坏的重要原因之一，至今，国内外对这一问题的研究甚少。本文提出了一个新的方法，用以分析受沉陷作用的埋地管道的反应，该方法选取跨越非沉陷区和沉陷区的埋地管道为研究对象，用三次曲线模拟沉陷区管道的几何大变形，推导出沉陷区段管道在几何大变形条件下的受力平衡方程的内力递推公式，用弹性地基梁模型模拟非沉陷区的管道变形，并用学陷区和非沉陷区交界面处的变形及力学协调条件给出了交界点     

Ultrasonic modelling research of earthquake response of underground lifeline engineering

Earthquake response of underground lifeline engineering is investigated by the method of ultrasonic model experiments in this paper. From general field conditions, two models of underground lifeline engineering, one for non-uniform field and the other for uniform field, are designed based on the similarity principle. Besides analysis of seismic phases, a series of analyses especially on particle vibration are carried out. The results show that: The shorter the epicentral distance, the greater are the intensity variation and the change rate of intensity variation of earthquake ground motion, so the more disadvantageous to underground pipelines. In soft covering layer, compressional waves mainly cause radial flexures deformation, but shear wave result in axial dilation deformation of the pipelines; when the thickness of the covering layer is smaller (less than seismic wave length), the rhythmic variation of the intensity of earthquake ground motion is controlled mainly by the wave length of seismic waves in the bedrock. The property of the covering layer has considerable effect on earthquake ground motion. For different covering layers, their effect on each component of earthquake ground motion is not the same. Owing to the effect of wave propagation, the ground is in different states of particle vibration at different times, and there is considerable difference in phase and intensity of particle vibration between two different covering layers near their junction line or surface. Because underground lifelines tend to vibrate with the particles of the earth around it, this results in different deformation of underground pipelines under different conditions. So, it is necessary to take corresponding anti-seismic countermeasures for pipelines according to their practical situations. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 104–110, 1992. This paper is part of the research supported by Funds of Doctoral Faculty of National Education Committee.     

Innovative mitigation method for buried pipelines crossing faults

A new remediation technique is proposed to mitigate large deformations imposed on buried pipeline systems subject to permanent ground deformation. With this technique, low-density gravel(LDG) with high porosity, such as pumice,is used as backfill in the trench containing the pipe near an area susceptible to PGD. This countermeasure decreases soil resistance, soil-pipe interaction forces and strain on the pipe as the pipeline deformation mechanism changes to a more desirable shape. Expanded polys...     

城市地铁爆破开挖对浅埋地下大直径管道的安全影响研究

在城市浅埋地铁爆破开挖中,经常遇到地下管网、涵洞等构筑物,而爆破地震效应对其影响范围和程度的正确评价就显得尤为重要。本文以长沙地铁爆破开挖为例,以现场实测数据为基础,采用有限单元法,对爆破振动下大直径混凝土污水管道的动力响应、变形和动应力等进行了计算,评价了爆破地震对管道的安全影响。研究表明:管道在控制爆破作用下是偏于安全的;爆心距是影响管道受到爆炸作用力影响大小的最主要因素;对于以实测数据为基础,采用加速度激励的时程分析方法以爆破振动对埋地管道的影响进行评价,是一种可行且较为精确的方法。     

砂土液化引起大位移对地下管道影响的非线性分析

地下管线是生命线工程的主要部分,已经成为现代工农业生产和城镇生活的大动脉。已有震害调查表明,饱和砂土液化引起的地基大变形(侧向变形和沉降)是导致强震区生命线工程震害的主要原因。采用三维非线性有限差分分析方法来研究砂土液化引起的大位移对地下管道的破坏特征,分析砂土液化的斜坡变形特征、孔隙水的演化过程。结果表明,砂土液化引起的大位移对地下管道有破坏作用,导致管道变形规律与其斜坡的位移规律相同,地下管线的变形随着振动频率和幅值的增加其非线性增大。     

四种地下结构抗震设计简化分析方法对比

在地下结构抗震设计简化分析方法中,强制反应位移法将土层变形施加在有限元模型侧边界模拟地震作用,反应加速度法将土层加速度施加到整个有限元模型上模拟地震作用,此外还有仅将土层加速度施加到土层模型上模拟地震作用的方法。上述方法均规避了反应位移法中关于弹簧刚度的取值问题,提高了计算效率。本文以1个双跨箱形结构为例,用动力时程分析的计算结果作为校核,分析了强制反应位移法、反应加速度法和仅将土层加速度施加到土体中的简化分析方法在不同侧边距条件下的计算精度,再结合常用的反应位移法,对比分析了4种简化分析方法的误差。分析结果表明:使用强制反应位移法时,侧边距取为1倍结构宽度导致的误差最小,反应加速度法和仅在土体施加加速度的简化方法对侧边距取值不敏感,反应位移法在角点造成的误差最大。     

Shaking table tests modelling small diameter pipes crossing a vertical fault

Local gas pipelines provide a valuable resource to urban areas and are often forced to cover unfavourable ground conditions in order to form a serviceable network. This can force pipelines through soil, which is subjected to permanent ground displacements due to faulting and strong vibrations due to earthquakes. Due to the inseparability of faulting from earthquakes it is pertinent to examine the combined effect of dynamic vibration and shear deformation of the surrounding soil on buried pipelines and a better understanding of the factors affecting pipe response to these inputs will enable more intelligent design of future pipe networks with the intention of reducing damage inflicted on pipes in extreme events. To advance understanding of this topic, a series of model experiments were performed under 1 g conditions on instrumented 20 mm diameter acrylic prototype pipes buried in dry Toyoura sand as well as a tyre derived aggregate (TDA) backfill trench surrounded by Toyoura sand crossing a vertical fault. The apparatus setup allowed faulting and dynamic input to be applied simultaneously to the model, which revealed that the simultaneous loading reduces the bending of a pipe and that installation of a pipe in a tyre derived aggregate backfill reduces the bending moment experienced by the pipe by up to 74% for small fault displacement and low levels of acceleration.     

地震断层作用下的埋地管道等效分析模型

地震作用下,活动断层附近的埋地管道易发生强度屈服、局部屈曲或整体失稳等形式的破坏,建立准确、高效的埋地管道在断层作用下的计算模型,对管道的抗震设计和震后安全状态评估具有重要的实用价值。本文采用非线性弹簧模拟远离断层处埋地管道的反应,基于管土之间小变形段管道处于强化阶段,提出一种改进的管土等效分析模型,进一步减小了管土之间大变形段的分析长度,从而提高了有限元分析效率。该模型采用ALA推荐的方法计算管土间的滑动摩擦力,可以考虑土体种类的影响;用Kennedy方法确定管道的计算长度。通过与精确模型比较,验证了管土等效模型的合理性和有效性。     

Pipe–soil interaction for segmented buried pipelines subjected to dip faults

This paper describes an investigation of pipe–soil interaction equations suggested by currently used pipeline seismic design codes and the applicability of these equations to segmented pipelines. The results of computer‐aided analyses were compared to results obtained in full‐scale experiments on a segmented ductile iron pipeline 93 mm in diameter and 15 m in length. The pipeline was installed 600 mm below the ground surface in a sandy soil compacted to two different subgrade reaction values. The type of fault considered was a reverse fault with an intersection angle of 60° with the pipeline, and the fault movement was a total of 350 mm in three same steps in the fault trace direction. The findings of this study demonstrate the necessity of considering the nature of soil behavior in pipe–soil interaction equations and the effects of connection joints on the integrated response of pipelines to fault‐induced ground deformations. A new combination of equations constituting a direction‐wise selection from among the equations proposed by currently used guidelines is introduced as a new series to describe pipe–soil interaction for segmented pipelines and is verified using the results of full‐scale experiments. Copyright © 2014 John Wiley & Sons, Ltd.     

Earthquake response of underground pipelines

Seismic response of underground pipelines is investigat?ed theoretically considering dynamic soil-pipe interaction. A lumped mass model of the pipe is employed with the soil reactions derived from static and dynamic continuum theories. The soil is supposed to be homogeneous or composed of two different media separated by a vertical boundary. Axial and bending stresses in the pipe due to travelling waves are examined. An extensive parametric study indicates that the axial stresses in the pipe are much higher than bending stresses. In a homogeneous medium, soil-pipe interaction reduces the stresses in the pipe compared to those calculated ignoring interaction. In a soil composed of two different media, the pipe stresses are highest close to the boundary and can exceed those predicted neglecting interaction.     

跨断层隔震管道分析

埋地管道在断层错动作用下的内力分析及其抗震措施一直是生命线工程的一个重要问题与研究热点。对地下管道在断层错位下的响应计算,取得的成果较多,比较经典的有Newmark-Hall方法和Kennedy方法。后来又出现基于壳模型的简化方法,如高田至郎提出的简化计算方法等。相对来讲,关于管道抗震措施的研究成果较少。本文提出一种抗震措施,进行了基于壳模型的有限元动力数值模拟,并与4种松到中密场地土条件下的埋地管道断层错位响应进行对比分析。计算结果表明,本方法中三种长度管道的最大轴向拉应变远小于埋地管道的最大轴向拉应变,而且最大轴向压应变亦不大。     

受沉陷作用埋地管道破坏判别方法

大地地震震害经验表明，场地的不均匀沉陷是导致埋地管线破坏地重要原因之一。提出一个适用的管道破坏判别方法十分重要本文提出了一个新的方法，用以分析受沉的埋地管道的反应，该方法发迹了沉陷区和非沉陷区都用弹性地基梁的分析途径，在沉陷区考虑了管道几何大变形，克服了现有方法公适用于无限远处发生最大沉陷的缺陷，适用于任何沉陷参数的情况。     

有缝重力坝动力非线性数值计算模型及其应用

对于有缝重力坝的分析，基于连续介质力学的界面单元-有限元方法难于比较精确地模拟缝间的接触应力，从而无法合理地估算坝体应力与变形。作者对于多体系统和分区连续介质所发展的非连续变形计算力学模型能够根据接触界面的本构特性及其力学和运动学约束条件精确地再现受力过程中界面相互作用力的传递与非连续变形状态，本文将其应用于有缝重力坝的动力分析。实例数值分析表明该模型的计算结果从定性上讲是合理的，并且为判断坝体缝隙的工作状态与界面应力提供了有力的依据。     

Dynamic response of pipelines to moving loads

Vibration of buried pipelines induced by moving axial and radial loads has been studied in this paper. A thin shell model has been used for the pipeline, which is assumed to be lying in an infinite isotropic homogeneous elastic medium. In order to allow for the possible motion of the pipe out of phase with the surrounding ground a very thin layer of viscoelastic material is assumed to separate the pipe from the ground. Calculations indicate the presence of the interfacial viscoelastic layer does not influence the pipe response in a significant manner. So all the numerical results presented here are for the case when the pipe is assumed to be perfectly bonded. These show that the maximum pipewall displacements and stresses occur in a soft soil at long wavelengths.     

A new proposal for simplified design of buried steel pipes crossing active faults

Simplified design methods for obtaining the maximum strain in pipelines crossing active faults proposed by Newmark, Kennedy and Wang have not considered the section deformation of the pipe. In this study, a new simplified method is developed for obtaining the maximum strain in steel pipes crossing faults considering non‐linearity of material and geometry of pipe section. It is assumed that the pipe will bend near the fault and the geometry of pipe in the longitudinal direction will change according to a bent deformation. On the other hand, the relation between maximum strain and bent angle has been obtained using a beam–shell hybrid FEM for different pipe‐fault conditions. The developed method can be used for calculating the maximum strains for fault‐crossing steel pipes with different angles of crossing both in tension and compression, by considering the deformation of the pipe cross‐section. Copyright © 2001 John Wiley Sons, Ltd.