爆炸地震波作用下埋地管线动力反应分析方法

在研究爆炸地震波破坏作用的基础上,理论分析总结了关于埋地管线在爆炸地震波作用下动力反应分析的三种方法,即波动分析方法、管—土相互作用方法和震动—变形模型分析法,并结合算例,用不同的方法对管线受力进行了计算和分析比较,据此优选震动—变形分析法作为爆炸地震波作用下埋地管线动力响应的分析方法。     

跨逆断层埋地管线受力特性的管土效应分析

断层错动引起的地表永久性大变形是导致埋地管线破坏的重要因素之一,埋地管线的断层反应特性受到土介质和管线材料等因素的影响,本文以逆断层位错作用下的无缝直埋地管线为研究对象,基于ABAQUS有限元分析软件,建立埋地管线-土介质的三维有限元数值分析模型,利用非线性接触描述管-土接触状态,考虑初始地应力条件的影响,对跨逆断层埋地管线的受力特性进行数值模拟分析,依据计算结果主要分析了位错量、管线材料、管-土相互作用、土介质、管径等参数对埋地管线断层反应的影响效应,并得到:管-土介质接触效应是管线断层反应分析中不可忽视的影响因素,粘聚力较小、硬度较低的中硬土介质中的埋地管线抗断层性能较优等有益结论。     

土体塌陷范围对埋地管线影响的研究

土体塌陷是导致埋地管线破坏的重要原因之一。为分析土体塌陷时埋地管线的受力情况,通过ANSYS有限元软件,将管线模拟成四节点薄壳单元,用等效土弹簧来模拟无限长埋地管线的边界,采用均布荷载加载来模拟埋地管道上方土体的作用,分析了不同范围土体塌陷情况下埋地管道的受力特性。通过模拟分析了埋地管线的应力应变,得到了埋地管线的控制截面,可为埋地管线的设计提供一定的理论依据。     

第三方载荷作用下埋地输气管道动力响应的数值模拟

强夯是导致埋地输气管道第三方破坏的主要载荷形式之一.强夯下埋地输气管道动力响应问题的本质是夯锤-土-埋地管道组成的体系在冲击荷载下的整体动力响应.利用LS-DYNA有限元商业软件,基于非线性动力学基本理论和动态算法,在半无限土介质中,通过对动力参数和接触参数的合理设置,在验证某工程实例的基础上,选取适当的本构关系,从夯击能量的大小、夯锤和管道之间的间距和管道表面复土深度三个方面对强夯冲击荷载作用下埋地输气管道的动力响应问题进行了数值模拟研究,得出了埋地输气管道在夯击荷载下的动力响应规律.结果表明,采用数值模拟方法对研究强夯冲击荷载作用下埋地输气管道的动力响应是可行的,其计算结果对埋地输气管道的风险评估、设计和施工具有一定的参考价值.     

爆炸地冲击临界深度研究

地冲击是钻地武器毁伤地下目标的主要因素;随着钻地深度的增加,爆炸时耦合到岩土介质中产生地冲击的能量份额逐渐增加,在达到某个深度后趋向一个固定值,该深度称之为临界深度,但具体数值国内外差异极大,造成了地冲击效应计算结果的极大混乱。在详细分析已有数据的基础上,明确将临界深度细分为2个不同的物理量,即'地冲击临界深度'和'宏观破坏临界深度',前者主要由爆炸瞬时压缩周围介质形成向外传播的应力波决定,后者由爆炸应力波传播和爆轰气体准静态高压膨胀做功综合决定,前者数值要远小于后者。'地冲击临界深度'概念的明确提出,很好地解决了当前钻地爆炸中地冲击效应计算结果差异显著的难题,指出将2种临界深度混同、物理概念不清是造成差异的根本原因。进而以地冲击应力波试验参数、地表粒子运动速度以及数值仿真结果为基础,分析获得了土中爆炸地冲击临界深度具体数值。统一以地冲击临界深度为基准,对已有数据进行重新整理发现国内外的耦合因子是基本一致的,揭示了地冲击临界深度是确实存在的,概念是准确合理的。     

地表爆炸荷载作用下的埋地管道应力分析

城市地下管线是保障城市运行的重要基础设施和"生命线",近年来,由地下管网问题导致管线爆裂等事故呈高发态势。确保埋地管道的安全使用,对保障城市安全具有重要意义。对于地表爆炸荷载作用下埋地管道应力如何计算、应力分布有何特点及其是否安全,是一个值得研究的问题。基于模拟的爆炸荷载,在考虑不同管道埋深、爆心距和炸药当量的情况下,利用FLAC3D软件模拟获得了爆炸荷载作用下埋地管道的响应,并对管道的变形、应力及应力分布特点进行了分析。通过最大Von Mises应力失效准则对管道进行安全性评价,得出了一定范围内背爆面的管壁更易遭到受拉破坏,且爆心距大于15 m的埋地管道基本不受影响的结论。研究成果对于埋地管道防灾减灾具有一定的意义。     

被动状态下地埋管线的地基模量

 地下工程基坑、隧道开挖产生的自由土体位移场会引起周边地埋管线(如市政给排水管线、煤气管道等)产生附加变形并受力。基于Winkler地基模型的位移控制分析方法,将自由土体位移作为外部荷载即被动位移施加于管线上,管线与土体的相互作用采用Winkler地基弹簧模拟,弹簧常数一般根据Vesic公式得到。在基于弹性理论的推导中,Vesic公式的前提条件是弹性地基梁置于弹性半空间地表,竖向集中力或弯矩(主动荷载)置于梁的中心位置,这与地埋管线的一定埋深以及位移的施加情况是不一样的。为考虑上述2种因素对Winkler地基模量的影响,进行相应的理论探讨,提出考虑埋深影响的位移作用下地基模量的理论公式,并基于该地基模量进行隧道开挖对邻近地埋管线影响的位移控制理论分析。通过与弹性理论法、离心机试验以及实际工程观测结果的对比,验证该方法的合理性和正确性。     

大当量爆炸地冲击毁伤效应的理论与试验研究Ⅱ：深埋洞室地冲击效应模拟试验系统研制

相似模拟试验是解决大当量爆炸下深埋洞室工程安全问题的重要研究手段,但长期以来受相关技术手段、设备限制,相关研究一直难以有效开展。本文采用自主研制与必要借鉴相结合的研发方式,解决了高地应力柔性均布长时加载、地冲击波形精细调控以及高地应力叠加地冲击静动组合加载等关键技术问题,研制了深埋洞室地冲击效应真三维模拟试验系统。在1∶50～1∶100几何及相应物理相似下,装置可实现高地应力加载、开挖扰动过程和爆炸地冲击效应的模拟,解决了原型试验受限,模拟手段匮乏的技术难题。采用该试验系统,对深部巷道在动静载组合作用下的响应机制进行研究,结果显示按均质岩体极限应力设计的工程安全埋深边界外,地冲击扰动可激活深埋岩体中构造岩块运动,造成工程局部严重破坏。测试结果表明,该装置运行稳定可靠,可真实再现冲击扰动下深埋洞室的毁伤过程,为深埋洞室抗大当量武器打击的安全防护研究提供了可靠的基础平台。     

土壤源热泵垂直U型地埋管换热的数值模拟

本文建立了垂直U型地埋管三维数值传热模型,采用FLUENT软件对其非稳态的流固耦合换热进行研究.在夏季工况下,模拟结果与实验相吻合.分析了回填材料导热系数、管内流速以及埋深对垂直U型地埋管换热的影响.计算结果表明,地埋管的单位埋深换热量与埋深成反比,而与流速和回填材料的导热系数成正比.     

大当量爆炸地冲击毁伤效应的理论与试验研究Ⅲ：深埋洞室地冲击效应模拟试验研究

为厘清开挖扰动和大当量爆炸地冲击扰动对深埋洞室破坏的影响机制，采用自主研制的深埋洞室地冲击效应模拟试验系统，开展从地应力加载、洞室开挖到地冲击扰动加载全过程的相似模型试验。试验模拟了600 m埋深洞室开挖过程，以及封闭爆炸当量90 kt、比例爆距为133 m/kt^1/3时的地冲击扰动诱发工程破坏现象。试验成功模拟了颗粒弹射、板裂和块体激活等现象。得到冲击扰动作用下洞周应力、应变和位移的变化规律以及深部洞室的破坏机制。证实了比例爆距为133 m/kt^1/3时，洞室处于轻微破坏区。此外，通过开展重复地冲击扰动下的洞室稳定性研究，成功模拟岩爆、板裂、掌子面坍塌等工程灾害，得到重复地冲击扰动下洞室的破坏机制。试验的成功开展，为大当量地下爆炸作用下深埋洞室防护和安全范围确定奠定了重要的基础。     

埋地管道在地震波作用下的抗震性能分析

埋地管道是一种特殊的地下结构 ,地震时由于管道与砂土等介质的相互作用而引起管道运动 ,在管道中产生地震应力。针对地震波作用下埋地管道的运动特点 ,运用振动和抗震动力学理论 ,推导了埋地管道的振动运动方程和管土间相互作用的传递系数 ,进而求出了管道最大的轴向应力和弯曲应力。最后 ,通过实例分析讨论了土及管道参数对埋地管道抗震性能的影响     

人防工程穿墙管线变形破坏计算研究

本文针对核爆炸及常规武器炮、炸弹爆炸破坏作用下,地下人防工程围护结构与周围岩土介质之间存在爆炸震动现象,建立了穿墙管线变形破坏反应的解析解和数值解计算模型。利用上述两种计算模型对算例进行了计算与分析,得出了一些有益的结论,可为人防工程穿墙管线的管材选择、穿墙设计、防护措施及安全评估提供理论指导。     

有接头埋管在地震行波作用下的弹塑性分析

针对具有柔性接头的地下埋管在地震波作用下的反应分析问题,基于反应位移法,将管体和接头进行等效均匀化处理建立简化的弹塑形管单元模型,推导了由这样的简化管单元模型构成的直管段在地震位移波作用下的位移计算公式。在求得等效管模型位移的基础上,再对每个管段和接头进行精细分析,求得管体及其接头的真实内力和变形。利用该方法对PVC管和铸铁管两种类型埋管进行了地震波作用下的反应分析,并与基于有限元分析的结果进行对比验证了方法具有充分的计算精度,可在地下埋管抗震设计中应用。     

Investigating peak stresses in fitting and repair patches of buried polyethylene gas pipes

Nowadays, polyethylene composes a large number of natural gas distribution pipelines installed under the ground. The focus of the present contribution is two fold. One of the objectives is to investigate the applicability of polyethylene fittings in joining polyethylene gas pipes which are electrofused onto the pipe ends and buried under the ground, by estimating stress distribution using finite element method. The second objective is to study the effectiveness of polyethylene repair patches which are used to mend the defected pipelines by performing a finite element analysis to calculate peak stress values. Buried polyethylene pipelines in the natural gas industry, can be imposed by sever loadings including the soil-structure interaction, traffic load, soil’s column weight, internal pressure, and thermal loads resulting from daily and/or seasonal temperature changes. Additionally, due to the application of pipe joints, and repair patches local stresses superimposed on the aforementioned loading effects. The pipe is assumed to be made of PE80 resin and its jointing socket, and the repair patch is PE100 material. The computational analysis of stresses and the computer simulations are performed using ANSYS commercial software. According to the results, the peak stress values take place in the middle of the fitting and at its internal surface. The maximum stress values in fitting and pipe are below the allowable stresses which shows the proper use of introduced fitting is applicable even in hot climate areas of Ahvaz, Iran. Although the buried pipe is imposed to the maximum values of stresses, the PE100 socket is more sensitive to a temperature drop. Furthermore, all four studied patch arrangements show significant reinforcing effects on the defected section of the buried PE gas pipe to transfer applied loads. Meanwhile, the defected buried medium density polyethylene gas pipe and its saddle fused patch can resist the imposed mechanical and thermal loads of 22°C temperature increase. Moreover, increasing the saddle fusion patch length to 12 inches reduces the maximum stress values in the pipe, significantly.     

Effect of surrounding soil on stress–strain response of buried pipelines under ground loads

In order to determine the stress–strain response of buried pipelines under the ground load, the pipeline–soil coupling finite element model was established. The mechanical behaviours of buried pipelines in the soil stratum and the rock stratum, as well as the effects of surrounding soil's elasticity modulus, Poisson's ratio and cohesion on stress and strain of buried pipelines were investigated. The results show that the maximum von Mises stress, high stress area, axial strain and plastic strain increase with the increasing ground load. Buried pipeline in the soil stratum is more prone to failure than in the rock stratum under the same ground load. The maximum axial compressive strain appears at the bottom of buried pipelines when there is no buckling, and the maximum tensile strain appears on the two sides. High stress area, the axial strain, the plastic strain and the plastic area decrease with the increase of the soil's elasticity modulus and cohesion. But the surrounding soil's Poisson's ratio has a small effect on the stress and strain of buried pipelines under the ground load. The results can provide a theoretical basis and reference for safety evaluation, repair and maintenance of buried pipelines.     

Instantaneous stress release in fault surface asperities during mining-induced fault-slip

Fault-slip taking place in underground mines occasionally causes severe damage to mine openings as a result of strong ground motion induced by seismic waves arising from fault-slip.It is indicated from previous studies that intense seismic waves could be generated with the shock unloading of fault surface asperities during fault-slip.This study investigates the shock unloading with numerical simulation.A three-dimensional(3D) numerical model with idealized asperities is constructed with the help of discrete element code 3DEC.The idealization is conducted to particularly focus on simulating the shock unloading that previous numerical models,which replicate asperity degradation and crack development during the shear behavior of a joint surface in previous studies,fail to capture and simulate.With the numerical model,static and dynamic analyses are carried out to simulate unloading of asperities in the course of fault-slip.The results obtained from the dynamic analysis show that gradual stress release takes place around the center of the asperity tip at a rate of 45 MPa/ms for the base case,while an instantaneous stress release greater than 80 MPa occurs near the periphery of the asperity tip when the contact between the upper and lower asperities is lost.The instantaneous stress release becomes more intense in the vicinity of the asperity tip,causing tensile stress more than 20 MPa.It is deduced that the tensile stress could further increase if the numerical model is discretized more densely and analysis is carried out under stress conditions at a great depth.A model parametric study shows that in-situ stress state has a significant influence on the magnitude of the generated tensile stress.The results imply that the rapid stress release generating extremely high tensile stress on the asperity tip can cause intense seismic waves when it occurs at a great depth.     

Segmentation of Pipe Images for Crack Detection in Buried Sewers

Abstract:   Assessing the condition of underground pipelines such as water lines, sewer pipes, and telecommunication conduits in an automated and reliable manner is vital to the safety and maintenance of buried public infrastructure. To fully automate condition assessment, it is necessary to develop robust data analysis and interpretation systems for defects in buried pipes. This article presents the development of an automated data analysis system for detecting defects in sanitary sewer pipelines. We propose a three-step method to identify and extract cracks from contrast enhanced pipe images. This method is based on mathematical morphology and curvature evaluation that detects crack-like patterns in a noisy pipe camera scanned image. As cracks are the most common defects in pipes and are indicative of the residual structural strength of the pipe, they are the focus of this study. This article discusses its implementation on 225 pipe images taken from different cities in North America and shows that the system performs very well under a variety of pipe conditions.     

基于系统可靠度的地下管网抗震设计

地下管网是生命线工程的重要组成部分。文章以地下管网整体有限元分析模型、基于物理机制的随机地震动场和概率密度演化方法为基础,发展地下管网的系统可靠度分析方法和基于可靠度的抗震设计方法。应用该方法,可以得到管网地震反应的概率密度函数和系统可靠度,进而以典型地下管网为例,具体说明这一设计方法。文中方法的创新性：①该方法针对的是整个地下管网结构而非简单的管线结构;②该方法可以完整获得管网结构不同部位和管网整体的随机反应信息,并据此实现管网内部和管网整体的抗震可靠度评价,从而以此实现基于整体可靠度的地下管网抗震设计。     

隧道开挖对有接头地埋管线影响的工程评价方法

隧道开挖产生的土体位移对地埋管线的影响不可避免,不仅会引起管线接头的相对旋转,甚至会造成损坏和泄漏。目前对有接头管线响应的研究方法较为复杂,大多基于数值分析方法,接头力学性质的影响考虑不够全面,已有的设计图表工程应用欠缺。结合连续管线的理论分析,考虑地层位移沉降曲线、管段刚度及接头刚度等影响因素,建立了有接头管线的工程评价方法,以分析隧道开挖对有接头地埋管线的影响。运用该方法对实际工程案例进行分析,并将计算结果与数值分析结果对比,验证本文方法的可靠性。本工程评价方法可以为实际管线工程安全预评估起到一定的作用。     

管道内预混气体爆炸的波形演化特征及超压预测模型

综合采用数值模拟、理论建模和实验验证方法,开展了平直管道内气体爆炸超压的预测方法研究。研究分析发现：爆炸波可以分为三种类型,即爆轰波、高速爆燃波和缓燃波,而且爆炸波形能够反映火焰燃烧和爆炸超压之间的关系,典型的爆炸波包含前驱冲击波、火焰压缩波和稀疏波三个部分。前驱冲击波的超压随着爆炸的传播不断增大,其与距离的关系可以用线性函数表征,火焰压缩波形成的第二次峰值超压与传播距离的关系也可以用线性函数表征,但其波形可以用指数函数表征。最后,实验验证了本文提出的爆炸波形函数的正确性,其可以很好地预测爆炸超压演化,而且与数值模拟结论基本相同。研究成果可以为管道或巷道内可燃气体爆炸超压预测及破坏评估提供理论依据。