Research on seismic survey design for doubly complex areas

The complex geological conditions in doubly complex areas tend to result in difficult surface survey operations and poor target layer imaging in the subsurface which has a great impact on seismic data quality. In this paper, we propose an optimal crooked line survey method for decreasing the surface survey operational difficulties and improving the sub-layer event continuity. The method concentrates on the surface shooting conditions, first, selecting the proper shot positions based on the specific surface topographic features to reduce the shot difficulties and then optimizing the receiver positioning to meet the prerequisite that the subsurface reflection points remain in a straight line. Using this method cannot only lower the shooting difficulty of rough surface condition areas but also overcome the subsurface reflection point bending problem appearing in the traditional crooked line survey method. On the other hand, we use local infill shooting rather than conventional overall infill shooting to improve sublayer event continuity and uniformity with lower survey operation cost. A model has been calculated and processed with the proposed optimal crooked line survey and local infill shooting design method workflow and the results show that this new method can work for seismic surveys in double complex areas.

Lessons learned from the “5.12” Wenchuan Earthquake:evaluation of earthquake performance objectives and the importance of seismic conceptual design principles

Many different types of buildings were severely damaged or collapsed during the May 12, 2008 Great Wenchuan Earthquake. Based on survey data collected in regions that were subjected to moderate to severe earthquake intensities, a comparison between the observed building damage, and the three earthquake performance objectives and seismic conceptual design principles specified by the national ＂Code for Seismic Design of Buildings GB50011-2001,＂ was carried out. Actual damage and predicted damage for a given earthquake level for different types of structures is compared. Discussions on seismic conceptual design principles, with respect to multiple defense lines, strong column-weak beam, link beam of shear walls, ductility detailing of masonry structures, exits and staircases, and nonstructural elements, etc. are carried out. Suggestions for improving the seismic design of structures are also proposed. It is concluded that the seismic performance objectives for three earthquake levels, i.e., ＂no failure under minor earthquake level, ＂＂repairable damage under moderate earthquake level＂ and ＂no collapse under major earthquake level＂ can be achieved if seismic design principles are carried out by strictly following the code requirements and ensuring construction quality.

Seismic performance of tunnel lining of side-by-side and vertically stacked twin-tunnels

The dynamic interaction between tunnel lining and its surrounding soil is a complicated issue as the magnitude of seismic wave from bedrock to the structure can be easily influenced by the geometrical layout and structural stiffness of the tunnel.A series of numerical analysis was conducted to study the dynamic response of the tunnel lining of side-by-side and vertically stacked double-tube tunnel since the inertia and kinematic interactions between the tunnel lining and the surrounding soil during an earthquake could induce excessive stresses to the lining itself due to the stiffness variation between the lining and the soil.Real earthquake ground acceleration was used as an input motion in the dynamic analysis.The interactive behavior of bending moment and axial forces,and the displacement of the tunnels were used to evaluate the effect of tunnel geometrical layout on the performance of the lining.It is found that the effect of earthquake on the axial thrust of the lining is insignificant,and there is a reduction of the bending moment in the lining due to the redistribution of the surrounding soil after the earthquake.

Seismicity of the Nairobi City area,Its Geotechnical Implications and Mitigation Measures

This paper is an attempt to determine how vulnerable the city of Nairobi is to earthquake attack and the potential disaster sites within it and its environs,how this affects the structural integrity of the its construction works and the sustainable way forward.Nairobi sits close to the eastern flanks of the Great Rift Valley and recent revelations that indicate the valley may be expanding at a rate of 2-3 mm per year due to tensional forces in the crust(Waithaka, 2001).The high heat flow beneath the crust is represented by the geothermal activities at Olkaria,

Basic dynamic characteristics and seismic design of anchorage system

Based on some assumptions,the dynamic governing equation of anchorage system is established.The calculation formula of natural frequency and the corresponding vibration mode are deduced.Besides,the feasibility of the theoretical method is verified by using a specific example combined with other methods.It is found that the low-order natural frequency corresponds to the first mode of vibration,and the high-order natural frequency corresponds to the second mode of vibration,while the third mode happens only when the physical and mechanical parameters of anchorage system meet certain conditions.With the increasing of the order of natural frequency,the influence on the dynamic mechanical response of anchorage system decreases gradually.Additionally,a calculating method,which can find the dangerous area of anchorage engineering in different construction sites and avoid the unreasonable design of anchor that may cause resonance,is proposed to meet the seismic precautionary requirements.This method is verified to be feasible and effective by being applied to an actual project.The study of basic dynamic features of anchorage system can provide a theoretical guidance for anchor seismic design and fast evaluation of anchor design scheme.

Application of the Common Offset Seismic Reflection Method to Urban Active Fault Surveys

The method and principle of common offset seismic surveys as well as the field data gathering and processing technique were introduced briefly. Through two urban active fault survey examples in Fuzhou and Shenyang, the efficiency and limitation of using the common offset seismic reflection technique to carry out urban active fault surveys were probed. The results show that this technique has the properties of high resolving power, better reconstruction of subsurface structures, and real-time analyzing and interpretation of investigation results on site. This method can be used to quickly locate objects under investigation accurately in the areas with thinner Quaternary overburdens and strong bedrock interface fluctuations.

颗粒阻尼器对输电塔线系统减震性能研究

对输电塔线系统进行缩尺模型振动台实验,从时域和频域的角度,对比了调谐质量阻尼器和颗粒阻尼器对输电塔的减震效果。利用ABAQUS建立了颗粒阻尼器控制输电塔线系统的离散元-有限元高精度耦合数值模型,对比了实验和模拟结果,并对塔线系统的耗能情况及颗粒阻尼器内部颗粒运动碰撞情况进行分析。研究结果表明:在地震激励下,颗粒阻尼器的减震效果较调谐质量阻尼器有更好的鲁棒性;该文所建立的颗粒阻尼器控制输电塔线系统模型能够良好地反映试件的动力特性和地震响应;在颗粒阻尼器的控制下,塔线系统总能量降低24.12%。当颗粒之间的碰撞次数和颗粒与容器的碰撞次数满足一定比例关系时,颗粒阻尼器能实现更优的控制效果。

高速铁路预制装配式大跨度明洞衬砌地震响应的数值分析

结合某拟建高速铁路大跨度明洞穿越地层的工程地质和地貌,建立了地层与装配式明洞衬砌的三维有限元模型,并基于粘弹性人工边界,采用时程分析法研究了装配式大跨度明洞衬砌的地震响应,给出了装配式明洞衬砌受地震影响的薄弱部位。结果表明:在高烈度震区装配式明洞衬砌拱肩和拱脚部位以及管片接头处的应力和位移响应较大,是装配式明洞衬砌的薄弱部位,在结构设计时需加强此部位的配筋。此外,与EI波和汶川波相比,天津波对预制装配式明洞衬砌的影响较大。

防屈曲支撑框架抗震性能影响因素的模拟分析

本文旨在研究防屈曲支撑(BRB)平面布置方式和抗侧刚度比两种综合因素对防屈曲支撑钢筋混凝土框架(BRBF)的抗震性能影响,以及框架中BRB的合理布置方案。通过采用OpenSees软件建立了4、8和12层的BRBF空间模型,并进行双向地震作用下的结构弹塑性时程分析,对比分析3种BRB布置方式与5种抗侧刚度比的组合工况下结构抗震性能,基于分析结果综合判定BRB最优布置方案。结果表明:在外框架、内框架和全框架的3种支撑布置方式中地震损伤程度的控制效果分别可达30%、40%和60%,且效果随抗侧刚度比的增加而递增;BRB的设置显著增加了底柱的最大轴力,其中全框架布置方式在3种支撑方式中表现出最优的降低结构竖向反应的效果。BRB最优布置方案组合为内框架布置与刚度比1.0和全框架布置与刚度比2.5。研究成果可为每层采用相同BRB布置方式的规则钢筋混凝土框架结构的加固设计提供参考。

考虑变墩高效应的小半径曲线梁桥地震易损性研究

为分析墩高变化形式对小半径曲线梁桥地震易损性的影响,以某互通式立交匝道桥第2联为背景,设计渐变型、凹岛型、凸岛型3种墩高变化形式曲线梁桥进行地震易损性研究。在提出的压弯剪扭耦合作用破坏的基础上,采用集中铰-纤维模型的桥墩建模方法,通过SeismoStruct有限元软件建立3种墩高变化形式曲线梁桥模型;选取符合Ⅲ类场地特性的50条地震波,利用能力需求比法,以位移延性比为损伤指标,研究不同变墩高形式下桥墩与支座的地震易损性。结果表明:当小半径曲线梁桥采用3种墩高变化形式时,以弯曲受力为主的中、高墩在地震作用下发生完全破坏概率较低,以弯剪或剪切受力为主的矮墩在强震作用下发生完全破坏概率较大,变墩高曲线梁桥可以适当提高矮墩的抗震能力;凹岛型墩高变化形式会增加矮墩的损伤概率,在抗震设计中应避免选择该墩高变化形式或尽可能优化墩梁连接方式;墩高变化形式对于支座的易损性影响小于对桥墩的影响。

地震测线-稀疏节点联合初至层析速度建模

近年来含油气盆地的深层勘探逐渐成为研究热点,如何提高深层的速度建模精度是地震勘探所面对的关键问题.常规地震测线偏移距短,无法记录含有深层结构信息的长偏移距初至数据,采用地震测线初至到时的建模方法不能建立深层速度模型.地震节点记录具有广角和宽方位的特征,在全球/区域地震学中被广泛应用于深部结构研究.但是,地震节点的密集布设会剧烈增加节点数量和野外工作量,而地震节点的稀疏布设则难以保证浅部速度结构的建模精度,引起深部速度建模的不准确.针对该问题,我们提出一种新的地震测线-稀疏节点联合初至层析速度建模方法:将常规地震测线与稀疏地震节点结合形成新观测系统,联合地震节点和常规测线的初至走时,采用地震层析成像开展油田深层速度建模.数值实验和实际应用结果均显示,地震测线与稀疏节点联合可以在浅层和深层均形成良好的数据覆盖,初至层析在浅层和深层均具有较高的建模精度.在大节点间距情况下联合常规地震测线和节点的联合方法比常规测线采集仅增加很少工作量,但其层析速度建模仍具有较高的建模精度,与高成本的高密度节点数据建模结果精度相近.本文方法可以方便地应用于常规地震测线采集的区块,在增加很少工作量的情况下实现深层高精度速度建模,对于含油气盆地的深层勘探具有重要意义.

反平面线源荷载作用下浅埋圆形非完全粘结隧道动力响应研究

为加深理解波源距离和非完全粘结对地震波散射的影响规律,结合位移不连续模型、波函数展开法、Graf公式和镜像方法推导了反平面线源荷载下浅埋圆形非完全粘结隧道动力响应的级数解,并通过衬砌内外边界条件残余量与级数解截断项数的关系校验了该解的精度。通过对该级数解进行参数分析,系统地探讨了衬砌与围岩的接触刚度、衬砌模量、衬砌厚度、隧道埋深和波源距离等因素对衬砌内表面位移和周向剪应力的影响。结果表明:衬砌与围岩的接触刚度对隧道的动力响应具有显著的影响,尤其在某些较小接触刚度情况下隧道动力响应幅值可能非常大;增大衬砌模量会减小位移,但同时会导致周向剪应力增加;增大衬砌厚度能同时减小位移和周向剪应力;增大隧道埋深会使最大位移和周向剪应力向隧道拱顶附近移动;增大线源与隧道的水平距离会使隧道背波侧相对幅值增大。

P波入射下山体-隔震层-隧道的整体响应分析

采用高精度间接边界元方法(IBEM)开展了山体-隔震层-隧道的整体响应分析,研究了P波入射下柔性隔震层对高斯形山体内双线隧道地震动响应的减弱作用。在隔震层与围岩之间考虑了碎土的错动滑移,以模拟不完美交界面,并系统讨论了隔震层弹性模量、厚度、P波入射频率等因素对隧道地震动响应的影响。数值模拟结果表明:适当增加隔震层厚度可以显著降低隧道应力,有效提升隔震效果,应力降低幅度约达50%以上,且使得结构受力更为均匀;随着隔震层材料的弹性模量减小,隧道动应力数值明显减小,有效减少了其应力放大区的面积,从而有效避免因地震而导致的衬砌裂缝。

输电线路抗震韧性评估方法研究

输电线路抗震韧性研究有助于确定震后输电线路功能损失和恢复时间,为震后电力系统恢复提供重要参考。基于2008年汶川8.0级地震后成都、绵阳、德阳、广元和阿坝5个地区的输电线路震害资料,分析了输电线路功能失效、恢复情况,建立了功能失效、恢复时间与破坏情况的对应关系函数,结合韧性定义给出输电线路功能损失累积函数,划分了韧性水平等级,形成了以电压等级、长度、地形地貌为参数的输电线路抗震韧性计算方法。使用该方法对我国某地区输电线路进行试算,计算结果与以往对输电线路震害情况的定性判断基本相符,能够揭示出该地区输电线路在低烈度时损失较轻、在高烈度时损失较重的基本规律。

综合物探技术在城市地铁勘察中的研究与案例浅析

在城市地铁勘察中,岩溶、断裂及软土等不良地质是主要工程隐患,严重威胁着工程后续的施工建设安全,在常规地质勘察之外,有必要采用有效且适宜于城市环境的物探手段予以查明,提高勘察资料的可靠度和覆盖面。城市环境复杂,场地条件限制多,不同物性干扰强,整体物探环境恶劣。笔者以徐州地铁4、5号线勘察为例,首先针对具体场地条件进行物探环境评估;其次对各种物探方法进行技术适应性分析,提出场地环境与技术方法的最佳耦合;最后,总结出一套适用性与操作性强的物探技术模式。综合对比分析结果表明:①微动、瞬变电磁等技术可作为城区主要的地面物探手段,能初步查明岩溶、断裂等地质体的位置与赋存特征;②在岩溶精细探测上,孔间CT(电磁波)技术能进一步圈定岩溶的发育规模和空间位置;③地面与孔间物探的合理选用或联合应用,能够提供不同勘察阶段、不同勘察精度所需的地质资料,满足城市地铁勘察需求。

地震动多角度斜入射下无压隧洞地震响应分析

为研究地震动多角度倾斜入射下无压水工隧洞动力响应特征和规律,采用黏弹性人工边界模拟无限地基的辐射阻尼和弹性恢复力,将地震动转化为人工边界节点上的节点力,以实现地震动的非一致性输入.通过ABAQUS建立水工隧洞模型,将不同入射角度P波、SV波输入模型中,分析隧洞衬砌结构的环向应力、径向应力随地震动入射角度、缩放系数、隧洞埋深、洞身直径以及衬砌厚度的变化.结果表明,同一地震动入射倾角下,随着入射方位角的增大,环向应力逐渐减小,径向应力逐渐增大.地震动峰值加速度(Peak Ground Acceleration,PGA)显著影响衬砌结构应力,并且应力数值随PGA的变化呈整数倍增大;随着隧洞埋深由浅埋向中埋、深埋发展,隧洞应力先逐渐增大后减小,后趋于稳定;随着洞身直径的增大,环向、径向应力分别受P波、SV波影响,洞身直径每增加2m,环向、径向应力分别增大约16%、21%;衬砌厚度每增加0.1m,径向应力降低10%左右,当地震波垂直隧洞轴线入射时,衬砌厚度超过1.0m后,对应力的影响效果减弱.

高烈度地震区高铁隧道衬砌背后空洞特征及地震响应

为提高强震区含病害铁路隧道的安全性,通过隧道检查车对29座高速铁路隧道衬砌背后空洞测试,借助有限差分方法研究空洞对隧道结构安全性的影响。结果表明:高铁隧道衬砌背后空洞极易出现在拱顶,占比80.00%;空洞纵向长度出现频率最高区间为2~4 m,占比46.49%;与衬砌表面最小距离为0.3~0.55 m的空洞占比78.93%,空洞常伴随衬砌厚度不足病害;衬砌背后空洞改变围岩-支护的接触状态,进而结构的惯性力和强制位移改变,震时位移和应力状态也随之变化;空洞导致所在部位的结构内力改变,结构安全系数降低19.51%~95.27%;随着空洞的环向角度、径向深度、纵向长度的增加,结构安全系数降低。衬砌背后空洞将导致高铁隧道衬砌的震时安全性显著降低。研究成果可为含病害高铁隧道抗震设防提供借鉴。

海底地震勘探测线设计与实现

测线设计是海底地震勘探过程中必不可少的环节,设计的常规测线和声学定位测线是作业过程中作业船航行的主要参考线。海底地震勘探过程中使用的常规测线和声学定位测线一般为直测线或者折测线,本文详细阐述了直测线的设计原理及方法,并且分别叙述了忽略拐点和凑整拐点这两种不同拐点处理方式的折测线的设计规则,以及声学定位测线的相应设计流程。此外,本文通过编程实现了相应的常规测线和声学定位测线设计功能,经检验,设计成果合格,可以推广使用。

山岭隧道洞口段边坡及衬砌震害机理

为探明山岭隧道洞口段的震害机理,以期为该段落的震后恢复和抗减震措施提供参考,依托“5·12”汶川地震中受损严重的龙溪隧道,采用数值模拟分析了隧道洞口段边仰坡及衬砌的地震动力响应,系统研究了山岭隧道洞口段边仰坡开裂及滑移、落石、崩塌、衬砌开裂几类震害的产生机理。研究表明:1)隧道洞口边仰坡开裂是水平地震惯性力的张拉作用超过坡体自身的抗拉强度所形成的;2)边仰坡滑移是边仰坡开裂后,水平地震惯性力的斜向分力超过坡体抗剪强度使裂缝贯通,并沿坡体内某一软弱面产生滑移;3)落石、崩塌是坡表松散岩土体的累积拉应力超过自身抗拉强度引发的;4)衬砌横向开裂是地震荷载沿轴向反复的拉压作用使衬砌拉应变不断累积并超过混凝土极限应变所致;5)衬砌纵向开裂是在于横向地震作用下衬砌产生方向交替急剧变化的附加弯矩,混凝土受到方向交替的拉压作用,使其强度明显降低产生纵向开裂。

辽河拗陷大民屯凹陷S281块高密度宽线二维地震采集实践

辽河拗陷大民屯凹陷S281块X井钻井显示该块油气潜力较大,但以往地震资料采集时间早,覆盖次数较低,成像精度差,导致主体断裂位置和微断裂体系难以落实,制约区块成藏解释和后续开发.为此,开展了高密度宽线二维地震资料采集,并基于采集数据开展了观测系统退化分析.研究结果表明,新采集的高密度宽线二维地震成像剖面较以往三维地震成果剖面断点更清晰,断裂系统刻画更清楚,构造形态更自然,层间信息更丰富,信噪比更高,落实了的西部斜坡带的构造特征;超高密度、极小面元对高陡构造和断裂刻画更清楚,是提高复杂地质目标成像的有效方法;退化处理说明S281块的地震资料采集观测系统的面元边长不能大于12.5 m,最大炮检距不能小于3500 m,覆盖次数不能小于1200次.本研究可为大民屯凹陷西部斜坡带的下步地震资料采集和勘探开发提供借鉴.