Impact of surface-reflected seismic waves on the seismic isolation performance of circular tunnel isolation layers

Seismic isolation is an effective strategy to mitigate the risk of seismic damage in tunnels.However,the impact of surface-reflected seismic waves on the effectiveness of tunnel isolation layers remains under explored.In this study,we employ the wave function expansion method to provide analytical solutions for the dynamic responses of linings in an elastic half-space and an infinite elastic space.By comparing the results of the two models,we investigate the seismic isolation effect of tunnel isolation layers induced by reflected seismic waves.Our findings reveal significant differences in the dynamic responses of the lining in the elastic half-space and the infinitely elastic space.Specifically,the dynamic stress concentration factor(DSCF)of the lining in the elastic half-space exhibits periodic fluctuations,influenced by the incident wave frequency and tunnel depth,while the DSCF in the infinitely elastic space remain stable.Overall,the seismic isolation application of the tunnel isolation layer is found to be less affected by surface-reflected seismic waves.Our results provide valuable insights for the design and assessment of the seismic isolation effect of tunnel isolation layers.

A joint absorbing boundary for the multiple-relaxation-time lattice Boltzmann method in seismic acoustic wavefield modeling

Conventional seismic wave forward simulation generally uses mathematical means to solve the macroscopic wave equation,and then obtains the corresponding seismic wavefield.Usually,when the subsurface structure is finely constructed and the continuity of media is poor,this strategy is difficult to meet the requirements of accurate wavefield calculation.This paper uses the multiple-relaxation-time lattice Boltzmann method(MRT-LBM)to conduct the seismic acoustic wavefield simulation and verify its computational accuracy.To cope with the problem of severe reflections at the truncated boundaries,we analogize the viscous absorbing boundary and perfectly matched layer(PML)absorbing boundary based on the single-relaxation-time lattice Boltzmann(SRT-LB)equation to the MRT-LB equation,and further,propose a joint absorbing boundary through comparative analysis.We give the specific forms of the modified MRT-LB equation loaded with the joint absorbing boundary in the two-dimensional(2D)and three-dimensional(3D)cases,respectively.Then,we verify the effects of this absorbing boundary scheme on a 2D homogeneous model,2D modified British Petroleum(BP)gas-cloud model,and 3D homogeneous model,respectively.The results reveal that by comparing with the viscous absorbing boundary and PML absorbing boundary,the joint absorbing boundary has the best absorption performance,although it is a little bit complicated.Therefore,this joint absorbing boundary better solves the problem of truncated boundary reflections of MRT-LBM in simulating seismic acoustic wavefields,which is pivotal to its wide application in the field of exploration seismology.

Application of passive source surface-wave method in site engineering seismic survey

Site engineering seismic survey provides basic data for seismic effect analysis. As an important parameter of soil, shear-wave velocity is usually obtained through wave velocity testing in borehole. In this paper, the passive source surface-wave method is introduced into the site engineering seismic survey and practically applied in an engineering site of Shijingshan District. By recording the ubiquitous weak vibration on the earth surface, extract the dispersion curve from the surface-wave components using the SPAC method and obtain the shear-wave velocity structure from inversion. Over the depth of 42 m under- ground, it totally consists of five layers with interface depth of 3.31, 4.50, 7.23, 17.41, and 42.00 m; and shear-wave velocity of 144.0, 198.3, 339.4, 744.2, and 903.7 m/s, respectively. The inversion result is used to evaluate site classification, determine the maximum shear modulus of soil, provide basis for further seismic hazard analysis and site assessment or site zoning, etc. The result shows that the passive source surface-wave method is feasible in the site engineering seismic survey and can replace boreholes,shorten survey period, and reduce engineering cost to some extent.

Numerical modeling of global seismic phases and its application in seismic phase identification

Earthquake data include informative seismic phases that require identification for imaging the Earth's structural interior.In order to identify the phases,we created a numerical method to calculate the traveltimes and raypaths by a shooting technique based upon the IASP91 Earth model,and it can calculate the traveltimes and raypaths for not only the seismic phases in the traditional traveltime tables such as IASP91,AK135,but also some phases such as pPcP,pPKIKP,and PPPPP.It is not necessary for this method to mesh the Earth model,and the results from the numerical modeling and its application show that the absolute differences between the calculated and theoretical traveltimes from the ISAP91 tables are less than 0.1 s.Thus,it is simple in manipulation and fast in computation,and can provide a reliable theoretical prediction for the identification of a seismic phase within the acquired earthquake data.

Seismic responses of high concrete face rockfill dams:A case study

Seismic responses of the Zipingpu concrete face rockfill dam were analyzed using the finite element method. The dynamic behavior of rockfill materials was modeled with a viscoelastic model and an empirical permanent strain model. The relevant parameters were obtained either by back analysis using the field observations or by reference to parameters of similar rockfill materials. The acceleration responses of the dam,the distribution of earthquake-induced settlement, and the gap propagation under the concrete slabs caused by the settlement of the dam were analyzed and compared with site investigations or relevant studies. The mechanism of failure of horizontal construction joints was also analyzed based on numerical results and site observations. Numerical results show that the input accelerations were considerably amplified near the top of the dam, and the strong shaking resulted in considerable settlement of the rockfill materials, with a maximum value exceeding 90 cm at the crest.As a result of the settlement of rockfill materials, the third-stage concrete slabs were separated from the cushion layer. The rotation of the cantilever slabs about the contacting regions, under the combined action of gravity and seismic inertial forces, led to the failure of the construction joints and tensile cracks appeared above the construction joints. The effectiveness and limitations of the so-called equivalent linear method are also discussed.

Probabilistic analysis of ultimate seismic bearing capacity of strip foundations

This paper presents a reliability analysis of the pseudo-static seismic bearing capacity of a strip foundation using the limit equilibrium theory. The first-order reliability method(FORM) is employed to calculate the reliability index. The response surface methodology(RSM) is used to assess the Hasofer e Lind reliability index and then it is optimized using a genetic algorithm(GA). The random variables used are the soil shear strength parameters and the seismic coefficients(khand kv). Two assumptions(normal and non-normal distribution) are used for the random variables. The assumption of uncorrelated variables was found to be conservative in comparison to that of negatively correlated soil shear strength parameters. The assumption of non-normal distribution for the random variables can induce a negative effect on the reliability index of the practical range of the seismic bearing capacity.

Dynamic behavior of single-layer latticed cylindrical shells subjected to seismic loading

The single-layer latticed cylindrical shell is one of the most widely adopted space-fl'amed structures.In this paper,free vibration properties and dynamic response to horizontal and vertical seismic waves of single-layer latticed cylindrical shells are analyzed by the finite element method using ANSYS software.In the numerical study,where hundreds of cases were analyzed,the parameters considered included rise-span ratio,length-span ratio,surface load and member section size.Moreover,to better define the actual behavior of single-layer latticed shells,the study is focused on the dynamic stress response to both axial forces and bending moments.Based on the numerical results,the effects of the parameters considered on the stresses are discussed and a modified seismic force coefficient method is suggested.In addition,some advice based on these research results is presented to help in the future design of such structures.

Seismic electric signals in seismic prone areas

The Varotsos-Alexopoulos-Nomicos （VAN） method of short-term earthquake prediction was introduced in the 1980s. The VAN method enables estimation of the epicenter, magnitude and occurrence time of an impending earthquake by observing transient changes of the electric field of the Earth termed seismic electric signals （SES）. Here, we present a few examples of SES observed in various earthquake prone areas worldwide.

中国石化油藏地球物理二十年发展与思考

油藏地球物理技术是综合应用多种地球物理资料与油藏动静态信息进行复杂油藏精细表征和动态监测的跨学科技术,对于提高油藏的储量动用程度和提高采收率具有重要的意义,是当前地球物理技术的重要发展方向。系统回顾了中国石化油藏地球物理提出的背景和过去二十年的发展历程,梳理了油藏地球物理技术系列,总结了在油藏地球物理基础研究、井中地球物理技术、多尺度资料联合反演、地球物理约束确定性建模、时移地震剩余油气预测、地震地质工程一体化、微地震油藏监测等方面的技术创新和应用效果。面对中国油气田勘探开发的深层、深水、非常规及老油田(“两深一非一老”)形势和一体化、智能化、绿色化挑战,油藏地球物理在油气产业技术致胜阶段仍然大有可为,要持续创新油藏地球物理技术,井、震、动、模一体化联合和人工智能应用,构建高水平的油藏地球物理勘探开发一体化、地质工程一体化解决方案,支撑油藏全生命周期建设。

滇中引水工程隧洞综合超前地质预报分析及应用

针对隧洞施工过程中不同工程地质条件下何种超前地质预报方法预测更为准确、更为适用和单一方法精确度不够、适用性不强的问题,分别介绍了基于地震波法的长距离隧洞超前地质预报技术和基于电磁法的中、短距离隧洞超前地质预报技术原理及特点,依据其工作原理、工作方式、预报距离等特点,探讨了不同超前地质预报方法的优、缺点及其最适用的工作场景,总结出一套实用性强的综合超前地质预报流程。依托滇中引水工程大理Ⅱ段两个隧洞的工程实例,利用所提出的综合超前地质预报流程,分别介绍了结合长距离的隧道地震预报(TSP)法、中短距离的瞬变电磁法和探地雷达法对断层破碎带和裂隙水等不良地质体的综合预报研究。首先,通过长距离预报方法对地质灾害危险程度进行分级、识别高危地段,再通过短距离预报方法对不良地质体进行更精确的识别与定位,综合分析3种超前地质预报方法的地球物理响应特征,可以推断出不良地质体的类型及其空间分布特征;其次,通过探地雷达探测溶蚀波场特征的案例分析,可以推断出溶蚀的物性特征、规模及其空间分布特征。预报结果与隧洞掌子面开挖揭示的结果基本一致,验证了3种超前地质预报方法预报隧洞不良地质体的可靠性,也证实了所提出的综合超前地质预报流程的实用性,有助于指导物探工作者对不良地质体进行更精确的预报,确保隧洞施工安全。

钻爆法机械化施工隧道随钻地震波超前地质探测技术研究

为适应我国隧道建设机械化、智能化、无人化发展趋势,围绕钻爆法机械化施工隧道,提出以凿岩台车破岩振动为震源的钻爆法机械化施工隧道随钻地震波超前地质探测技术。针对凿岩台车多震源连续激发带来的地震数据波场混叠、有效信息难以识别问题开展相关研究,提出VMD-SVD-RobustICA三臂混合先导信号分离方法与脉冲反褶积-小波域互相关地震记录重构方法,可实现三臂混合先导信号的分离与有效反射信号的提取。工程实践证明,利用凿岩台车搭载式无线高精度探测装备,该技术可初步实现“边钻边探”,降低预报环节对钻爆法机械化施工隧道正常施工带来的影响。最后,明确该技术目前存在的问题及解决思路。

采用钢管榫卯节点连接的节段预制拼装桥墩抗震性能研究

为分析钢管榫卯节点连接构造对节段预制拼装桥墩抗震性能的影响,以福建省某互通立交桥匝道桥为背景进行研究。首先进行钢管榫卯节点连接的足尺节段预制拼装桥墩试设计,采用MIDAS Civil软件建立实桥模型,对试设计的足尺节段预制拼装桥墩开展静力承载力验算;然后按1∶3.75比例缩尺,设计、制作1根整体现浇桥墩(RC)试件和1根钢管榫卯节点连接的节段预制拼装桥墩(PSBP-MTJ)试件,开展拟静力试验;最后对比分析两试件的破坏模式、滞回曲线、骨架曲线与延性、累积滞回耗能、刚度退化与残余位移。结果表明:两试件的破坏模式类似,均为整体压弯型破坏,PSBP-MTJ试件塑性铰区因墩底灌浆套筒的存在而上移;两试件滞回曲线饱满无捏缩,耗能能力相当;PSBP-MTJ试件水平承载能力较RC试件提高约19%;PSBP-MTJ试件的拼装节段之间无剪切滑移出现,预应力筋延缓了其刚度退化,显著提高了其自复位性能,其残余位移仅为RC试件的67%,且残余位移与最大位移比值显著小于未采用无粘结预应力筋连接试件。

松动及加固后木结构燕尾榫节点抗震性能对比试验

古建筑木结构燕尾榫节点松动是一种常见的残损模式,为研究节点松动对抗震性能的影响,参照宋《营造法式》殿堂二等材的尺度要求,考虑不同松动程度、不同松动程度补强加固和不同松动程度震损后加固的节点,共制作了3组12个节点试件,对其进行低周反复荷载作用下的抗震性能试验.结果表明:不同松动程度补强加固节点及不同松动程度且有损伤加固节点的破坏模式,与不同松动程度节点的破坏模式相似,榫头和卯口挤压变形明显,榫头被拔出,普拍枋与柱顶接触处出现剪切破坏,补强加固节点榫头拔出量明显减小;各节点滞回曲线均有明显“捏缩”效应,整体呈反“Z”型,补强加固节点的滞回环饱满程度略好;随节点松动程度增加,刚度及承载力均降低,随拔榫量的增大,其减小幅度降低;随节点转角增大,耗能能力逐渐减弱,补强加固节点的耗能及防脱榫能力明显高于未加固节点.节点在松动后仍具有较好的变形能力.

长庆安塞油田剩余油开发区DAS井地联采技术探索与实践

中国石油集团东方地球物理勘探有限责任公司结合长庆安塞油田开发区“三低”和“双复杂”的典型特点,面对老油田剩余油预测突出问题,从井地、井震协同一体化研究思路出发,开展国内首次面向开发区剩余油预测的多井DAS三维井地联采技术探索与实践,通过井地联合勘探实现地面地震测量和井中地震测量的优势互补,取得了良好成果。(1)通过井震同步井驱处理,三维地震资料保真度和分辨率明显提升,有效频带拓宽8%以上。(2)通过井地、井震一体化油藏静态描述剩余油预测研究,减少了单一地面地震解释成果多解性,可分辨更小地质单元,为油田精细开发提供了可靠的资料依据。(3)DAS三维井地联采配套技术支撑了安塞油田新增地质储量,并通过低产低效井组挖潜措施调整,提产效果明显。通过本次研究得出,井地联合立体探测是提升油田开发过程中微幅构造刻画和储层、流体预测精度的有效技术手段,形成的技术可推动物探技术向油田开发延伸、向井地立体探测发展,可为老油田稳产增效、推进高效开发提供支撑。

雅安地区监测井水位预测效能对比研究

为提高监测井水位映震效果的判别准确度并提升预测效能,本文运用不同方法对雅安地区两条断裂附近的6口监测井水位的映震效果开展了对比判别研究。首先,使用差分法对监测井水位数据进行处理和分析。然后,将水位数据与区域地震活动性的两种参数(能级和最大震级)相结合,分析区域地震活动性与水位波动的关系。接着,在时域和频域两个层面对该组合序列进行分析处理。最后,采用Molchan图表法检验5种方法的预测效能,并选出最佳处理方法及断裂附近预测效能最优的监测井。结果表明:水位与地震活动性参数结合处理相比单独使用水位差分法具有优势,前者能够准确排除地震活动性对水位异常的干扰。6口监测井的最优预测方法各不相同,最优预测天数均在60 d内。通过比较监测井水位对地震的预测效能检验结果,确定了两条断裂区域预测效能最优的监测井。虽然水位与地震活动性两种参数结合处理并不适用于所有监测井,但该方法能够体现水位受地震活动性影响的程度。

陆梁油田侏罗系油藏薄储层预测方法及应用

陆梁油田侏罗系油藏具有一定开发潜力。侏罗系西山窑组自上而下为3段,含油层为西山窑一段,据段内多个泥岩隔层分布进一步将西一段划分为2个油层组5个小层,具“一砂一藏”特点。由于5~10 m薄砂层很难直接在地震剖面上成像,为侏罗系西山窑组油藏的薄储层精准预测带来了一定困难。为了解油层及薄储层的平面及空间展布特征,本次研究基于钻井、测井、试油等资料,以三维叠后地震数据的子波主频,建立研究区地震记录波形与合成记录波形两个信号的互相关函数计算衰减系数Qf,并完成时-频衰减高精度合成记录标定。通过确定地震波阻抗识别门槛值,结合薄储层地震振幅属性数据体与岩性解释的储层特征分析资料,输出西山窑组西一段地震波阻抗反演剖面及油层厚度图。预测结果表明,开发井油层厚度为5~8 m薄砂体,与实际资料准确率达90%,为油藏开发扩边提供了理论依据。

瞬变电磁法和地震反射波法在不良地质洞段超前地质预报中的应用

物探方法是超前地质预报的主要手段,通过不良地质体与围岩物性参数差异,及时发现和预测地质条件的变化。较完整一完整围岩岩体物性参数与不良地质体物性参数存在较明显差异,有利于分辨出不良地质体;但是在地质条件差洞段的不良地质体与围岩岩体物性参数差异极小,不利于分辨出不良地质体,使得岩体质量情况和地质灾害风险预报难度极大。本次采用瞬变电磁法与地震反射波法的综合物探法,在滇中引水工程大理Ⅱ段Ⅴ_(特)类岩体开展专项超前地质预报工作,主要利用岩体视电阻率、应力梯度、纵波波速、横波波速等参数对未开挖段岩体质量和可能存在的地质灾害风险进行预测。创造性地通过“日进尺”这一指标间接对开挖岩体破碎程度进行评价,经对比,预报成果中符合长度占实际开挖过程中问题段长度的85.1%,预报结果与开挖成果较为吻合;此外,对坍塌失稳段、突泥涌水段也有明显反映,为该方法组合在不良地质洞段超前地质预报中的应用提供了借鉴。

孔—巷瞬变电磁隧道不良地质体超前预报方法研究

在复杂环境下进行隧道施工,需要解决对溶洞、裂隙等小规模不良地质体的精细探测。为此设计了掌子面前方存在小规模溶洞的隧道施工模型,在掌子面中心点向隧道施工方向打一个钻孔,将电性源放入孔中进行激发,在掌子面上进行阵列式数据采集,采用时域有限元方法对模型进行瞬变电磁三维正演计算。结果表明可以通过源的移动对目标体进行电磁测深,通过掌子面上电磁场分布规律确定不良地质体的平面位置。采用孔中电性源激发的方式,可以提高瞬变电磁对小规模溶洞的探测能力,为隧道环境中提高超前预报精度提供一种可行性手段。

梁端弹簧型自复位钢筋混凝土框架基于性能的抗震设计方法

梁端弹簧型自复位框架(self-centering frame, SCF)结构作为一种新型抗震结构体系,通过梁柱节点铰接构造来使整体结构抗侧刚度弱化,并在梁端设置钢板弹簧来给节点设定确定的转动刚度,从而达到地震作用下结构减震和震后结构自复位的目标。在已有理论和试验研究的基础上,对梁端弹簧型自复位框架的抗震设计方法进行了研究,并给出了此类结构的抗震性能水准以及结构的抗震设计流程。结合一幢三层自复位耗能框架结构的设计实例,进行基于性能的结构抗震设计,通过有限元模拟对该结构的动力响应与常规框架进行比较分析。结果表明:梁端弹簧型自复位耗能框架结构具有较小的加速度响应和层剪力响应,以及良好的变形性能。研究结果表明,梁端弹簧型自复位框架结构具有优越的抗震性能。

蜀南自贡地区茅口组岩溶储层成因及地震预测方法

近年来,四川盆地下二叠统茅口组大量非构造圈闭钻井获得高产,证实了岩溶储层是茅口组岩性气藏的一个重要控制因素。但岩溶储层的成因及地震响应特征尚不明确,不同地区的岩溶储层预测方法不尽相同。通过对蜀南自贡地区茅口组构造特征、地层特征和岩溶储层地震响应特征研究,得出以下5方面认识:①台内滩相是岩溶储层发育的物质基础,自贡地区茅口组台内滩相主要在茅三段和茅二b段发育;②东吴运动差异抬升是研究区岩溶储层的主控因素;③断层形成于茅口组沉积之后,茅口组顶部岩溶储层受后期局部持续风化控制,茅口组内部岩溶储层受后期断层改造控制;④距茅口组顶距离不同,岩溶储层地震响应特征不同,茅三段表层型岩溶储层物性与茅口组顶部波峰振幅呈负相关,茅二b段内幕型岩溶储层物性则与茅口组内部波峰振幅呈正相关;⑤表层型岩溶储层在平面上不依赖断层且具有一定规模。