Numerical simulation of damage in high arch dam due to earthquake

Based on the assumption that concrete is macroscopic homogeneous, the cracking evolution process and damage mode of high arch dams are studied in consideration of the heterogeneity of concrete in mesoscale. The bilinear damage evolution model and the damage evolution model expressed in power function with descending section are adopted to combine with the Mohr-Coulomb criterion with tension cut-off to investigate the crack development and fracture mode of high arch dams under the action of an earthquake. The analysis result of a high arch dam in China under design shows that cracks that take place in concrete are caused by excessive tensile stress. The cracks initiate at the middle of the dam top and distribute at the upper half of the dam while the rest of the parts remain intact. This conclusion agrees with the model test result. __________ Translated from Shuili Xuebao, 2008, 39(7): 848–853 [译自: 水利学报]     

高拱坝振动台地震破坏试验研究及数值仿真

 以大岗山拱坝模型的动力破坏试验为基础,从试验和数值计算角度,对整体拱坝动力特性、薄弱部位、破坏形态以及抗震性能进行研究。采用和混凝土性能相似的脆性模型材料,通过逐级加载的方式在振动台上对整体拱坝进行从弹性到破坏整个过程的模型试验,分析坝体动态特性、加速度和应变的变化规律。并采用弹脆性损伤模型对混凝土拱坝在地震作用下损伤破坏的全过程进行数值仿真,探讨拱坝动力破坏过程、破坏形态,并与试验结果进行对比分析。结果表明：模型试验和对原型进行的数值模拟所得到的破坏过程和破坏形态都较为接近。在顺河向地震作用下,顶拱的坝中部位为地震应力最高的区域,是坝体薄弱的部位,整体拱坝首先在该位置出现裂纹,其次是顶拱距左右两岸1/4拱圈处。在强震作用下,拱向和梁向裂缝贯穿上下游,将导致拱顶中部的混凝土脱离坝体,丧失壅水功能。试验和计算结果相互印证,可呈现高拱坝在强烈地震作用下的损伤破坏过程及破坏形态,确定抗震薄弱环节,为混凝土高坝的抗震功能设计提供基础。     

拱坝基础不对称性影响研究

结合国内外一些由于两岸基础不对性造成拱坝的影响实例，基于多次的地质力学模型试验和三维有限元计算分析，就锦屏一级高拱坝地形、地质条件不对性对拱坝整体稳定的影响和加固措施的选择进行了探讨。试验和数值结果均显示：上游坝踵拉应力偏大，下游出现拉应力。坝体应力不对称；左岸变形大于右岸，并且出现斜裂缝，超载能力偏低。通过研究，建议采用垫座及锚索等加固措施，使大坝整体处于平稳状态。     

基于速率相关混凝土损伤模型的高拱坝地震响应分析

不同应变率下混凝土受拉及受压的动力试验表明,混凝土的弹性模量、抗拉强度、抗压强度及相应的极限应变等重要参数与应变率和加载历史密切相关。根据已有试验结果,通过引入损伤张量随应变率的变化建立了应变率相关的混凝土非线性损伤模型,对300米级的高拱坝的地震响应进行了计算,并分析了拱坝应变率和拉、压损伤的分布规律。结果表明,由于地震荷载引起的应变率在坝面的分布不同,坝面各处的动态性能变化并不一致,由此引起的混凝土强度和刚度的变化,对于高混凝土拱坝的动力响应和安全性评价有重要影响。     

基于跨尺度精细方法的面板坝面板损伤演化尺寸效应分析

中国面板坝建设规模正突破200~300 m级跨越,研究地震面板损伤破坏对特高坝抗震性能和安全控制具有重要意义。引入Quadtree跨尺度建模和非线性SBFEM-FEM耦合分析方法,联合土体广义塑性模型、弹塑性接触模型和混凝土塑性损伤模型,研究了高面板坝面板地震精细损伤演化过程。研究表明：面板损伤区主要发生在高程0.6H~0.9H区间附近;随顺坡向网格细化,损伤越趋局部化,越能合理地反映面板顶部的损伤破坏现象,建议顺坡向面板尺寸取0.5~1.0 m。面板大部分区域法向划分2层或1层网格可满足计算精度,但对顶部局部区域,可考虑分3层网格。基于Quadtree-SBFEM-FEM的跨尺度分析方法,实现了面板的精细化损伤演化规律研究,可为工程地震薄弱区域的精准定位和抗震安全控制方法的有效性分析提供重要参考和指导。     

Challenges of high dam construction to computational mechanics

The current situations and growing prospects of China’s hydro-power development and high dam construction are reviewed, giving emphasis to key issues for safety evaluation of large dams and hydro-power plants, especially those associated with application of state-of-the-art computational mechanics. These include but are not limited to: stress and stability analysis of dam foundations under external loads; earthquake behavior of dam-foundation-reservoir systems, mechanical properties of mass concrete for dams, high velocity flow and energy dissipation for high dams, scientific and technical problems of hydro-power plants and underground structures, and newly developed types of dam-Roll Compacted Concrete (RCC) dams and Concrete Face Rock-fill (CFR) dams. Some examples demonstrating successful utilizations of computational mechanics in high dam engineering are given, including seismic nonlinear analysis for arch dam foundations, nonlinear fracture analysis of arch dams under reservoir loads, and failure analysis of arch dam-foundations. To make more use of the computational mechanics in high dam engineering, it is pointed out that much research including different computational methods, numerical models and solution schemes, and verifications through experimental tests and filed measurements is necessary in the future. Selected from Computational Mechanics, Proceedings of the Sixth World Congress on Computational Mechanics in Conjunction with the Second Asian-Pacific Congress on Computational Mechanics, Tsinghua University Press & Springer, 2004, 154–166     

基于工程类比的小湾拱坝安全评价

 将工程类比法推广到拱坝极限承载力的研究,对于小湾拱坝等超高拱坝,由于其条件复杂,工程规模巨大,简单按照规范设计是不够的,应该以已建工程为对比对象,通过类比研究确定合理的安全标准。基于相同网格尺寸、相同材料模型以及相同计算软件,以已建工程二滩和Kolnbrein加固前后作为类比研究对象,对小湾拱坝的坝踵开裂及极限承载力进行研究。以超大规模精细有限元模型精确模拟坝体的底缝和地基的地形、断层、蚀变带加固措施以及建基面卸荷带,以全面评估地质条件对极限承载力的影响。分析结果表明：小湾拱坝极限承载能力要明显强于Kolnbrein加固前后,略逊于二滩。但正常工作条件下帷幕的安全裕度不大。     

Features of seismic hazard in large dam projects and strong motion monitoring of large dams

Earthquakes can affect large dam projects in many different ways. Usually, design engineers are focussing on ground shaking and neglect the other aspects. The May 12, 2008 Wenchuan earthquake has damaged 1803 dams and reservoirs, and 403 hydropower plants with an installed capacity of 3.3GW. Among these dams were the 132-m-high Shapai RCC arch dam and the 156-m-high Zipingpu concrete face rockfill dam. These recently completed dams are dam types which, up to now, have not experienced strong ground shaking. The widespread mass movements have caused substantial damage to dams and surface powerhouses in Sichuan. The different features of earthquake hazard are presented, i.e., ground shaking, faulting and mass movements. It is proposed to prepare project-specific safety plans for all dams, which consist of a matrix where the possible hazards and the corresponding countermeasures are listed. The earthquake behaviors of the Sefid Rud, Zipingpu and Shapai dams, which, in the past, have experienced strong ground shaking from nearby earthquakes, are discussed. Finally, the need for strong motion instrumentation of large dams is discussed. It is proposed that major dams with large damage potential, dams located in areas of high seismicity, and dams showing signs of abnormal behavior be equipped with strong motion instruments.     

Features of seismic hazard in large dam projects and strong motion monitoring of large dams

Earthquakes can affect large dam projects in many different ways. Usually, design engineers are focussing on ground shaking and neglect the other aspects. The May 12, 2008 Wenchuan earthquake has damaged 1803 dams and reservoirs, and 403 hydropower plants with an installed capacity of 3.3GW. Among these dams were the 132-m-high Shapai RCC arch dam and the 156-m-high Zipingpu concrete face rockfill dam. These recently completed dams are dam types which, up to now, have not experienced strong ground shaking. The widespread mass movements have caused substantial damage to dams and surface powerhouses in Sichuan. The different features of earthquake hazard are presented, i.e., ground shaking, faulting and mass movements. It is proposed to prepare project-specific safety plans for all dams, which consist of a matrix where the possible hazards and the corresponding countermeasures are listed. The earthquake behaviors of the Sefid Rud, Zipingpu and Shapai dams, which, in the past, have experienced strong ground shaking from nearby earthquakes, are discussed. Finally, the need for strong motion instrumentation of large dams is discussed. It is proposed that major dams with large damage potential, dams located in areas of high seismicity, and dams showing signs of abnormal behavior be equipped with strong motion instruments.     

小湾水电站混凝土拱坝温度裂缝分析

针对小湾水电站双曲混凝土拱坝实际条件,参照相关的控制拱坝裂缝理论与实践,论述分析了在施工过程控制温度应力,从而控制拱坝裂缝的目标和具体方法,为混凝土拱坝施工过程提供指导。     

Earthquake analysis of arch and gravity dams including the effects of foundation inhomogeneity

Dam-foundation interaction plays an important role in the design of earthquake-resistant concrete arch and gravity dams. Geological conditions of the dam canyon are usually very complicated; however, in the literature, the damfoundation interaction analysis is often carried out based on the premise of a homogeneous unbounded foundation. In this paper, the effect of foundation inhomogeneity on the seismic response of arch and gravity dams was studied by means of scaled boundary finite element method (SBFEM). In order to satisfy the similarity requirement of SBFEM and simplify the computational effort, a subdomain approach and a conical representation of an unbounded foundation were proposed. The way of partitioning the domain and the selection of open angle and bottom radius of the cone model on the accuracy of the result were examined. Numerical examples show that the proposed approach is rational and efficient. Cases of foundation inhomogeneity with stiffness varying in accordance with an exponential function along the radial direction, and cases of foundation inhomogeneity with stiffness discontinuity and with weak interlayer strata on the earthquake response of concrete arch dams as well as gravity dams were analyzed. It was found that a homogeneous idealization of the unbounded foundation may sometimes greatly underestimate the maximum earthquake stress response of the dam. Therefore, taking into account the effect of foundation inhomogeneity for the earthquake safety assessment of concrete arch and gravity dams has great significance.     

高拱坝基础大垫座及周边缝设置研究

 提出高拱坝基础承载力对建基面的要求,讨论坝肩与河床基础大垫座及周边缝的工作机制、大垫座及周边缝设置的非线性分析特点以及其与高坝整体稳定的关系。指出大垫座设置对基础刚度的对称性、大坝整体稳定性有显著提高的效应。结合高拱坝(英古里、李家峡拱坝和锦屏I级拱坝)实例,详细讨论高拱坝在基础设置垫座后的安全度及坝踵、坝址应力分布优化情况。拱坝所提出的问题对我国目前的高拱坝建设具有指导意义。     

应变率对拱坝地震反应的影响

根据混凝土动力抗拉抗压试验成果和一致黏塑性模型的概念,考虑应变率和静水压力的影响,将混凝土静态HTC四参数模型改造成一致黏塑性HTC四参数本构模型,并用这个模型对某高拱坝进行了非线性地震反应分析,并与线弹性模型和率无关HTC四参数模型的结果进行比较,探讨应变率对拱坝地震反应的影响,结果表明考虑应变率的影响后,拱坝的应力和塑性应变都发生了较大的变化。     

复杂地基上高拱坝开裂与稳定研究

研究复杂地基上高拱坝坝面开裂与稳定的力学机制,这些机制涉及到大坝温度变化、大坝的基础弱化、渗流影响等.首先从分析大坝坝面裂纹细观开裂扩展的主轴本构力学机制、节理岩体的宏观开裂强度条件.然后提出大坝破坏的机构条件作为大坝整体稳定的判据.最后结合复杂地基的溪洛渡拱坝,运用提到的开裂与稳定模型,分析大坝在超载工况下,裂纹从细观裂纹扩展到宏观开裂,以至大坝失稳的全过程;分析建基面的点安全度随超载变化规律以及大坝的整体稳定.结果显示提到的分析方法有较好的应用价值.     

高土石坝地震安全控制标准与极限抗震能力研究

基于土石坝震害调查和原型观测资料分析，针对高土石坝的坝坡稳定、坝体地震永久变形以及混凝土面板接缝位移3个影响高土石坝安全的主要因素，初步建议了相应的地震安全控制标准，并应用于高心墙堆石坝和面板堆石坝的极限抗震能力计算分析。结果表明：按规范设计的高土石坝具有较强的抗震能力，其极限抗震能力在0.50g以上，可抵抗9度以上地震而不致于出现灾难性后果；高土石坝的极限抗震能力与相应的地震安全控制标准密切相关，按照本文建议的标准，高心墙堆石坝坝坡稳定是其极限抗震能力的控制因素，高面板堆石坝面板周边缝安全是其极限抗震能力的控制因素。     

混凝土大坝结构损伤检测振动法的可行性

首先对大坝安全监测与无损检测方面的研究现状、存在的问题进行了综述;在此基础上,阐述了大坝结构损伤检测振动法的基本概念及特点,对振动法在其他领域应用的研究情况作了简要介绍;并根据笔者的数值模拟研究结合其他相关研究,以及对一实际拱坝的初步测试,着重分析了用振动法进行混凝土大坝结构损伤检测的可行性,得出了用振动法检测大坝的结构损伤是完全有可能的;最后指出了用振动法进行混凝土大坝结构损伤检测还需要研究的问题.     

Dynamic failure analysis of concrete dams under air blast using coupled Euler-Lagrange finite element method

In this study, the air blast response of the concrete dams including dam-reservoir interaction and acoustic cavitation in the reservoir is investigated. The finite element (FE) developed code are used to build three-dimensional (3D) finite element models of concrete dams. A fully coupled Euler-Lagrange formulation has been adopted herein. A previous developed model including the strain rate effects is employed to model the concrete material behavior subjected to blast loading. In addition, a one-fluid cavitating model is employed for the simulation of acoustic cavitation in the fluid domain. A parametric study is conducted to evaluate the effects of the air blast loading on the response of concrete dam systems. Hence, the analyses are performed for different heights of dam and different values of the charge distance from the charge center. Numerical results revealed that 1) concrete arch dams are more vulnerable to air blast loading than concrete gravity dams; 2) reservoir has mitigation effect on the response of concrete dams; 3) acoustic cavitation intensify crest displacement of concrete dams.     

基于微震监测的大岗山高拱坝坝踵蓄水初期变形机制研究

 混凝土高拱坝坝踵是蓄水初期阶段拱坝安全的重点关注部位。通过构建国内首套高拱坝坝踵微震监测系统,实现对蓄水初期阶段大岗山拱坝坝踵区微破裂的实时监测,探究坝踵蓄水初期变形机制及其与微震活动性的关系。采用人工敲击试验确定坝踵等效P波波速为4 300 m/s,系统定位误差小于8 m。对系统获取的事件波形进行噪声滤除,并在自动定位基础上进行人工二次校核,提高定位精度,验证了微震监测技术应用于大体积混凝土工程的可行性。分析认为：蓄水初期阶段,大岗山高拱坝坝踵区微震活动性与库水位密切相关,微震事件聚集区实现从坝踵向坝趾的转移,坝踵压缩变形减小,而坝趾区变形量增加。此外,通过拱坝坝踵区微震变形演化过程,揭示了导流洞下闸蓄水前940 m高程基础廊道拱顶裂缝产生的根本诱因。研究成果可为混凝土高拱坝微震监测和真实工作性态研究提供参考。     

混凝土面板坝面板动力损伤有限元分析

联合采用混凝土塑性损伤模型和堆石料弹塑性本构模型,建立了面板堆石坝弹塑性动力分析方法,研究了地震荷载作用下混凝土面板的损伤发生和发展过程。计算结果表明：地震时,在0.65H（H为坝高）附近顺坡向拉应力最大,面板首先在该部位出现损伤,同时由于鞭稍效应,0.85H面板附近也出现损伤;采用损伤模型,损伤部位的面板出现软化,应力得到释放,计算结果比线弹性模型更加合理;采用塑性损伤模型可以反映混凝土面板渐进破坏过程,通过损伤变量可以清晰地了解面板的损伤分布和薄弱环节。此研究成果可以为进一步开展混凝土面板堆石坝极限抗震能力及抗震措施分析提供有效手段。     

Safety inspections and seismic behavior of embankment dams during the 2011 off the Pacific Coast of Tohoku earthquake

Immediately after the 2011 off the Pacific coast of Tohoku Earthquake, special safety inspections were carried out at over 300 dams in the affected area. Damage was identified at more than 10% of the inspected dams, with embankment dams showing a slightly higher ratio. Damage to embankment dams included relatively wide and/or long cracks mainly on the crest of earthfill dams, cracks in the impervious membrane of asphalt faced rockfill dams (AFRDs) and temporary increase in leakage. However, none of the dams under the jurisdiction of the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) sustained damage severe enough to threaten the safety of the dam, although an old earthfill embankment dam for an irrigation pond located outside the area regulated by the River Law was breached due to the earthquake. In this paper, the results of special safety inspections are summarized, as well as those of subsequent detailed investigations of several embankment dams under the jurisdiction of MILT. The features of the earthquake motions observed at the dam foundations during the earthquake and their effects on the behavior of embankment dams are also discussed.