Dynamic Analysis of Tunnel in Soil Subjected to Internal Blast Loading

The present work deals with the three-dimensional nonlinear finite element (FE) analyses of the tunnel in soil subjected to internal blast loading. The analyses are performed using the coupled Eulerian–Lagrangian analysis tool in FE software Abaqus/Explicit. The soil and reinforced concrete lining are modeled using the Lagrangian elements. The explosive Trinitrotoluene (TNT) is modeled using the Eulerian elements. The stress–strain response of soil, concrete, and reinforcement are simulated using strain rate dependent Drucker–Prager plasticity, concrete damaged plasticity and Johnson–Cook (J–C) plasticity models, respectively. The pressure–volume relationship of the TNT explosive is simulated using the Jones-Wilkins-Lee equation of state. Parametric sensitivity studies have been performed for different (1) tunnel lining thicknesses, (2) explosive charge weights and (3) angles of internal friction of soil. It is observed from the results that blast induced pressure on the tunnel lining increases with the increase in charge weight. Both the lining and the surrounding soil undergo significant deformation. The deformation of the tunnel lining increases with increasing charge weight and decreases with increasing lining thickness and increasing the angle of internal friction of soil. Blast-induced velocity in soil attenuates with increasing distance from the source of the blast.     

饱和软土层地铁列车运行引起的环境振动研究

我国沿海地区大量的地铁隧道都修建在饱和软土地层,饱和软土地层中地铁列车运行引起的环境振动逐渐成为社会关注的问题。以上海2号线某地铁区间隧道为研究对象,采用循环运动模型本构模型和水土耦合动力分析方法,分析了饱和软土中地铁列车运行引起的地表振动加速度以及振动位移响应规律,采用加速度振级对地表的振动强度进行了评价,分析了单次列车通过时引起的隧道下卧土层超孔隙水压力（EPWP）响应规律。计算结果表明,饱和土的振动响应比干土要小得多,地表水平向与竖向的振动规律明显的不同,超孔隙水压力沿隧道下方沿向是不断减少的,在距离隧道中心的纵断面上是先增加后减少。分析饱和土中地铁运行引起的环境响应规律,可为地铁沿线建筑物减隔振设计及沉降控制提供一定依据。     

Dynamic Analysis of Subway Structures Under Blast Loading

Public transit systems have become one of the targets of terrorist attacks using explosives, examples of which are the 1995 attack on Paris subway and the 2004 attack on Moscow subway. Considering the intense threats of terrorist attacks on subway systems in metropolitan areas, explicit three-dimensional Finite Element method was used to investigate the dynamic response and damage of subway structures under internal blast loading. The study was motivated by the fact that explosion in subway structure may not only cause direct life loss, but also damage the subway structure and lead to further loss of lives and properties. The study based on the New York subway system, and investigated the influences of various factors on the possible damage of subway tunnel, including weight of explosive, ground media, burial depth and characteristics of blast pressure. A mitigation measure using grouting to improve ground stiffness and strength was also analyzed. Considering the amount of explosive terrorists may use, the present study focused on small-diameter single-track tunnels, which are more vulnerable to internal blast loading and are common in New York City. Blast pressure from explosion was applied to lining surface assuming triangle pressure–time diagram, and the elasto-plasticity of ground and lining as well as their nonlinear interaction was taken into account in the numerical model. It is found from the numerical study that maximum lining stress occurred right after explosion, before the blast air pressure reduced to the atmospheric one, and it was more dependent on the maximum magnitude of air pressure than on the specific impulse, which is the area below the pressure–time curve. Small tunnels embedded in soft soil, with small burial depth, might be permanently damaged even by modest internal explosion that may be perpetuated by terrorists.     

爆炸地震波作用下盾构隧道动力响应分析

盾构隧道衬砌由于各种类型接头的存在而与整体式衬砌的力学特性存在较大差异。将盾构隧道衬砌结构看作由弹塑性铰链连接的刚性管片组成,考虑围岩介质的黏弹性,提出了爆炸地震波作用下盾构隧道动力分析的简化计算方法。采用该方法对南京地铁盾构段典型横断面进行了动力分析,研究了爆炸地震波入射角度、围岩介质特性及管片厚度对结构受力与变形的影响规律。分析结果表明:波入射角度对盾构隧道有很大影响,斜入射时结构的动力响应要大于垂直入射时结构的动力响应;围岩介质等级越高,围岩对隧道结构的约束越强,隧道的抗爆性能越好;管片厚度的增大会增大结构的内力,合理设置管片厚度有利于提高盾构隧道抗爆性能。     

花岗岩中强爆炸形成的应力封闭壳及其与爆炸当量的关系

以应力封闭壳理论为基础,对花岗岩介质中地下强爆炸产生的应力封闭壳效应进行了数值模拟。以100 t TNT当量的强爆炸为例,模拟了爆后空腔的回弹和封闭壳的动态形成过程,给出了形成稳定封闭壳后的径向应力、环向应力和爆心距的关系。计算了不同爆炸当量形成的应力封闭壳尺寸及其形成时间与爆炸当量的关系。计算结果表明,当空腔膨胀到最大尺寸之后,空腔开始回弹,此时开始形成应力封闭壳;当空腔回弹结束即形成稳定的空腔尺寸时,稳定的应力封闭壳也在该时刻形成;爆炸当量越大,形成的应力封闭壳的范围越大,当爆炸当量低于10 t TNT时,不能形成应力封闭壳。     

地铁隧道受平行向地裂缝错动影响数值分析

西安地铁3号线局部地段通过f7地裂缝上盘,并且和f7地裂缝近似平行。基于f7地裂缝长期水准监测预测的未来最大活动量值,采用数值方法,研究了西安典型的黄土、古土壤和粉质黏土地层下地铁隧道受平行向地裂缝活动的影响。通过逐渐变化地铁隧道衬砌外皮同地裂缝间的距离,计算了6种工况下地铁隧道衬砌的变形和内力。计算结果表明:当地铁隧道衬砌外皮距离地裂缝30m时,隧道衬砌是安全,并有一定的安全储备。     

Evaluation of liner responses due to non-uniform tail void grouting pressure

Tail void grouting initially does facilitate the action of ground loads around the lower half of the liner and no excess pressure being accumulated. However, at a later stage (almost at the completion of grouting), grout pressure becomes non-uniformly distributed around grout injection holes especially on the upper half of the liner. In the present study, the boundary and loading conditions were simulated by using a series of finite element analyses. It aimed to explore the effects of such temporary non-uniform loading conditions on development of the liner internal forces. The results obtained for tunnel with diameter of 6.0 m were presented. It was found that there were critical locations where application of non-uniform grouting pressure could result in large amounts of bending moment and deformation. Those critical locations; about ±30° to ±50° from crown of the tunnel, were about the locations where actual grouting was injected in the field. The stiffness of sub-soil beneath the tunnel invert had minor effect on the amount of induced structural forces. However, ground coverage was more important. The results, though cannot fully represent complicated tail grouting behaviours, provided a simple analytical procedure for exploring the effects of tail void grouting on the segmental liner.     

Lined Circular Tunnels in Elastic Transversely Anisotropic Rock at Depth

Closed-form solutions for displacements and stresses of both the liner and the rock are presented for a deep circular tunnel excavated in transversely anisotropic rock above or below the water table subjected to static or seismic loading. The solutions are obtained with the assumption of elastic response of rock and liner, tied contact between rock and liner, impermeable liner, plane strain conditions along the tunnel axis and simultaneous excavation, and liner installation. The liner of a tunnel placed below the water table must support, in addition to the rock stresses, the full water pressure, while a tunnel located above the water table must support only the rock pressures. The solutions presented for static loading show, however, that displacements and stresses of the liner and rock are the same when the tunnel is placed above or below the water table as long as the total far-field stresses are the same. With rapid loading, e.g. seismic loading, excess pore pressures may be generated in saturated rock, which induce a different response than that of a tunnel excavated in dry rock. The analyses indicate that stresses and displacements are more uniform when excess pore pressures are produced, which seems to indicate that pore pressure generation tends to reduce non-uniform response in anisotropic rock.     

Numerical prediction of blast‐induced stress wave from large‐scale underground explosion

This paper presents a numerical model for predicting the dynamic response of rock mass subjected to large‐scale underground explosion. The model is calibrated against data obtained from large‐scale field tests. The Hugoniot equation of state for rock mass is adopted to calculate the pressure as a function of mass density. A piecewise linear Drucker–Prager strength criterion including the strain rate effect is employed to model the rock mass behaviour subjected to blast loading. A double scalar damage model accounting for both the compression and tension damage is introduced to simulate the damage zone around the charge chamber caused by blast loading. The model is incorporated into Autodyn3D through its user subroutines. The numerical model is then used to predict the dynamic response of rock mass, in terms of the peak particle velocity (PPV) and peak particle acceleration (PPA) attenuation laws, the damage zone, the particle velocity time histories and their frequency contents for large‐scale underground explosion tests. The computed results are found in good agreement with the field measured data; hence, the proposed model is proven to be adequate for simulating the dynamic response of rock mass subjected to large‐scale underground explosion. Extended numerical analyses indicate that, apart from the charge loading density, the stress wave intensity is also affected, but to a lesser extent, by the charge weight and the charge chamber geometry for large‐scale underground explosions. Copyright © 2004 John Wiley & Sons, Ltd.     

FLAC3D在青岛地铁渗流场中的应用

首先,基于考虑衬砌和注浆圈的解析解,利用MATLAB软件编制了计算与自动绘图程序,研究水头、隧道半径、围岩渗透特性与衬砌渗透系数和隧道涌水量、外水压力的相互关系;其次,基于FLAC3D软件平台,通过数值解与理论解的对比,验证了数值模拟方法在隧道渗流场中应用的正确性。在此基础上,结合青岛地铁典型区间隧道,分析了隧道开挖阶段以及运营期的渗流场,并研究了在不同注浆圈厚度以及注浆圈渗透系数下隧道注浆圈的涌水量和外水压力。结果表明,在隧道周围施作注浆圈的方法来减少隧道的涌水量是可行的。注浆圈厚度越大,其渗透系数越小,隧道涌水量就越小,而外水压力变化规律与涌水量恰恰相反。研究成果为地铁隧道衬砌的设计和注浆圈范围的初步确定提供了参考依据。     

Effect of Underground Mine Blast Vibrations on Overlaying Open Pit Slopes: A Case Study for Daye Iron Mine in China

Investigating the propagation and attenuation of blast vibration in rock slopes is the key point to assess the influence of underground mine blasting on overlaying open pit slopes stability and determining the potential risk. In this paper, Daye Iron Mine in China has been chosen as the case to study the effect of blast vibrations on overlaying open pit slopes due to underground mine blast. Firstly, the characteristics of blast loadings are analyzed by the dynamic finite element method. Then, a three dimensional (3D) numerical model of the open pit and the underground mine is made, which is verified by the field monitoring data to prove its reliability. The effect of blast vibration on overlaying open pit slope due to underground mine blasting are discussed based on the peak particle velocity (PPV) and the peak effective tensile stress (PETS) distribution characteristics which are calculated and analyzed by inputting the obtained blast vibration data into the numerical model. The results show that the effect of present mining blasting on the stability of pit slopes are limited because the simulated maximum PPV and PETS of monitoring point on slopes are all < 0.747 cm/s and 0.738 MPa. At last, according to numerical simulations of the underground mine blasting, the PPV predicting formulas for the slopes in Daye Open Pit Iron Mine is proposed based on the classic Sadaovsk formula.     

一种简单的岩体地下洞室地震安全评价方法

提出了动应力集中因子代表值的概念,以合理反映地震荷载作用下地下洞室围岩的动应力集中程度,并将动应力集中因子代表值,作为洞室地震响应的关键特征来衡量洞室地震响应的大小。应用显示有限差分法,讨论了地震动加速度幅值、洞室埋深、围岩岩体级别、衬砌混凝土厚度、衬砌混凝土强度等级与动应力集中因子代表值的相关关系。研究表明,动应力集中因子代表值与这5个因素均近似呈线性关系。在此基础上给出了有（无）衬砌支护结构两种情况的地震安全评价公式,提出了岩体地下洞室的地震安全评价方法。应用提出的评价方法,分别对唐山余震地震作用下溪洛渡水电站超大型地下洞室群的地震安全性进行了评价,所得结果与Dowding-Rozen及Sharma-Judd的评价方法结果一致。分析还表明,文中提出的岩体地下工程的地震安全评价方法的评价结果是偏于安全的。     

A Modified Stress-Displacement Solution for a Pressure Tunnel with a Permeable Liner in an Elastic Porous Medium Based on a New Model

Referring to previous literature, the elastic problem for a deep pressure tunnel with a permeable liner in a saturated elastic porous medium that obeys Terzaghi’s effective stress principle is further investigated. In the analysis, the influences of the changes of the pore water pressure around the opening, the construction sequence of the tunnel, and the interaction between the liner and the surrounding geomaterial on the mechanical response of the tunnel are appropriately considered. Also, the influences of the relative liner thickness and rigidity and the relative distance of the point under investigation from the tunnel axis on the stress-displacement fields for various combinations of the mechanical and geometric parameters are numerically evaluated and discussed. The results indicate that both the support pressure and displacement increase monotonically with increasing liner rigidity and thickness. The influence of the tunnel excavation upon the displacement field is significantly larger than upon the stress field. Either too high or too low values for the relative rigidity and thickness of the liner are unfavorable for structural stability.     

地铁隧道竖向土压力荷载的计算研究

在地下结构按荷载结构模型计算分析时,如何确定作用在地下结构上的上覆土荷载的大小及分布是合理设计的关键。对于松软地层浅埋隧道,竖向土压力经常取全部土层厚度重量;而覆土厚度较大时采用坍落拱统计公式以及泰沙基理论或普氏压力拱理论等,这些理论公式在选用时还存在一些问题,值得进一步研究改进。根据北京地铁所处地层、隧道尺寸及埋深情况,采用常用覆土压力理论对北京地铁四、五、十号线标准断面安全度进行试算分析,提出了北京地铁隧道竖向土压力荷载计算方法,对地铁隧道及城市地下工程均具有借鉴参考价值。     

地铁列车振动作用下近距离平行隧道的弹塑性动力响应

利用有限元数值方法,对地铁列车振动荷载作用下近距离平行隧道结构的二维弹塑性动力响应进行模拟,分析了单列列车荷载以及双列列车荷载作用下土体-隧道结构体系的加速度和内力响应时程曲线。研究表明,列车动力荷载作用下的内力值要比无列车荷载作用下的内力值有较大程度的增加;在单列列车荷载作用下,另一相邻平行隧道的加速度响应、弯矩、轴力峰值要比列车运行所在隧道相应点处的响应值要小;在双列列车荷载作用下隧道结构体系动力响应值要比单列列车荷载作用下的动力响应值有显著增加。     

舟山灌门水道海底隧道钻爆法施工稳定性分析

以舟山灌门水道海底隧道为背景,依据地质资料,选取隧道典型横断面来研究钻爆法施工时围岩的稳定性。由典型横断面的几何参数和地质资料构建数值计算模型,采用国际上常用的计算模式模拟爆破荷载,根据FLAC3D动态计算的特点,将爆破荷载以等效应力的方式加载于模拟炮孔之上。数值计算结果表明,各关键点的位移、振动速度、加速度-时程曲线均满足隧道爆破变形规律,且振动速度峰值均小于规范要求临界值,爆破作用影响范围小于岩石覆盖层建议厚度,验证了岩层覆盖厚度建议值和爆破方案的合理性。最后,为了弄清岩石覆盖厚度和炸药量对围岩稳定性的影响,给出了不同岩石覆盖厚度和炸药量情况下的计算结果。所得结论对后续施工和类似工程具有一定的指导意义。     

地铁区间隧道内爆炸效应研究

为了评估南京地铁区间隧道内爆炸破坏效应,利用有限元分析软件LS-DYNA3D软件,计算了10kgTNT距隧道底部距离为1.1m的内爆炸工况。该软件中的化学爆炸空气冲击波模拟关键字避开了复杂烦琐的欧拉计算和ALE耦合分析过程,使得模型构建大大简化。计算得到了结构中不同关键节点的位移与速度时程曲线与不同单元的加速度时程曲线和最大主应变。结果表明地铁区间隧道在10kgTNT内爆作用下是安全的。     

移动环形荷载作用下饱和土中圆形衬砌隧洞动力响应研究

基于Biot理论,研究了饱和土中带有衬砌的圆形隧洞在移动环形荷载作用下的动力响应。假定衬砌为弹性体,土体为饱和多孔介质,引入两类势函数来表示土体、孔隙水和衬砌的位移,使隧洞的控制方程解耦。结合边界条件及连续条件,通过傅立叶变换得到频率-波数域中衬砌和土体的应力、位移和孔隙水压力解答,最后用傅立叶积分逆变换得到时-空域中的数值解。计算并比较了3种隧洞模型（弹性土体隧洞、饱和土体隧洞和饱和土衬砌隧洞）的动力响应分析。数值分析结果说明：（1）移动荷载速度对3种隧洞动力响应均具有较大影响;（2）弹性土体隧洞和饱和土体隧洞的动力响应具有明显区别,所以在富水地区的隧洞动力响应中土体应该视为饱和土体;（3）衬砌对隧洞动力响应有较大影响,故隧洞的动力分析中不能忽略衬砌作用。     

软弱饱和土夹层对地铁车站地震响应的影响分析

震害调查表明,当地下结构处于非均匀场地、软土层或在结构侧边存在软土夹层等复杂地质环境条件时,地下结构更易遭到损坏。因此,将对含有软弱饱和土夹层场地中地铁车站的地震响应进行分析。结合已有的单相介质和流体饱和多孔介质动力分析的显式有限元方法,考虑了土层中存在软弱夹层的情况,把软弱夹层模拟为流体饱和多孔介质,建立了适用于含软弱饱和土夹层场地中地铁车站结构地震响应分析的有限元方法;进行建模数值计算,分别给出了3条具有不同频谱特性的实际地震记录以P波形式入射下地铁车站结构关键位置的地震动响应,并分析了软弱夹层的位置、厚度等因素对地铁车站结构地震动响应的影响。分析结果表明,软弱夹层对地铁车站结构地震动响应具有非常不利的放大作用,且当软夹层位于地铁车站中部时,放大作用最不利。     

浅埋黄土隧道三层支护结构力学特性现场测试

为研究浅埋黄土隧道锚喷初支+初衬+二衬构成的3层支护体系力学特性,以某黄土隧道为依托,采用钢弦式传感器对围岩压力、初衬与二衬接触压力、二衬钢筋轴力、二衬混凝土应变、钢拱架应力等进行了系统测试与分析。结果表明：(1) 作用在左拱腰处的围岩压力较大,且稳定值为240 kPa;(2) 浅埋段按不同围岩压力计算公式得到压力值均大于围岩压力实测值,其中采用太沙基公式得到的压力值与实测值相对接近;(3) 该黄土隧道二衬全部受压,其分布形态呈明显的猫耳形,初支、初衬、二衬承受的荷载比例分别为51.34%、37.29%、11.38%;(4) 钢拱架整体以受压为主,在拱顶和拱腰处受力较大,接近屈服状态;(5) 初支发挥了一定的围岩自承能力,其与初衬共同承担了大部分围岩荷载,二衬主要为结构安全储备。