非均质无限地基上高拱坝的动力响应分析

地震作用下拱坝-无限地基的动力相互作用将对拱坝的地震响应产生重要影响。虽然很多学者曾经提出过各种相互作用的计算模型,但是绝大多数都是基于均质地基或有限地基假定的。利用比例边界有限元方法能够方便地模拟非均质无限域的优点,研究非均质无限地基对双曲高拱坝动力响应的影响。拱坝、地基和库水都利用比例边界有限元方法模拟,从而减少大量的计算量。在假定地基弹性模量随深度按指数变化的前提下,分析研究210 m高的大岗山双曲拱坝分别坐落在无质量地基、均质无限地基和非均质无限地基3种情况下的拱坝加速度频响曲线。通过与刚性较大的重力坝结构对比发现,无限地基的远场非均质特性对拱坝的动力响应影响较小。这是因为与重力坝不同,双曲高拱坝坝体与坝基之间的连接相对较为柔性,所以远场地基刚度变化对拱坝地震响应的影响较小。经进一步对近场地基刚度变化的分析发现,近场地基对拱坝地震响应产生一定影响。分析结果具有普遍意义,对强震区的高拱坝建设可以提供重要参考。     

混凝土坝-基岩地震动力相互作用时域有限元分析

混凝土坝地震响应分析是坝工安全评估的关键一步。坝与基岩动力相互作用对混凝土坝地震响应具有重要影响。因此,建立一个可考虑坝与基岩动力相互作用影响的数值分析方法是十分必要的。给出了分析混凝土坝–基岩系统地震响应的时域有限元法。在时域有限元分析中,地震波的输入以及地基辐射阻尼的模拟常常是2个十分重要的课题。基于柱面波动方程提出了能同时实现地震动输入和模拟地基辐射阻尼的方法,这种方法非常简单有效,几个数值算例验证了方法的精度和有效性。最后,对混凝土重力坝地震响应进行了数值分析,结果表明无限地基辐射阻尼的影响是显著的。     

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.     

地基刚度和不均匀性对混凝土大坝地震响应的影响

应用比例边界有限元方法进行了坝-水库-无限地基的动力相互作用分析。深入研究了无限地基刚度变化以及地基非均匀性对大坝地震响应的影响。计算了不同的均匀地基刚度和地基刚度随深度变化情况下Koyna大坝的频响曲线以及地震作用下大坝的时程响应。计算结果表明,地基刚度和不均匀性对大坝地震响应产生重要影响。对于均质地基刚度增加时,坝的地震响应随之增加;对于地基刚度随深度增加的不均匀地基,坝的地震响应增加迅速。此外还讨论了工程中广泛应用的无质量地基模型对于相互作用分析的适用性问题。     

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 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.     

汶川8.0级地震对典型高坝结构安全的影响分析

 汶川8.0级地震具有震级高、震源浅、破坏性强和次生地质灾害严重等特点。在对震区高坝灾情归类分析的基础上,选择典型的不同坝型高坝,包括宝珠寺重力坝、沙牌碾压混凝土拱坝、紫坪铺面板堆石坝等工程,从大坝距发震断裂距离、大坝基础处理及大坝结构类型的抗震性等因素对大坝结构安全的影响展开分析研究。结合在建的一批300 m级高坝,对抗震设防标准、水库诱发地震等问题进行讨论。结果表明：(1) 现行大坝抗震设计是可行的,300 m级高坝工程抗震能力仍需深化研究;(2) 大坝工程基础、抗力体经合理加固后,增强了岩体结构的整体性,可有效提高大坝及基础的抗震能力;(3) 高坝应急预案的设计与管理,流域性统一公共水电工程灾害应急平台建设有待加强;(4) 对水库诱发地震的研究需加强。     

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]     

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.     

Earthquake performance assessment of concrete gravity dams subjected to spatially varying seismic ground motions

This paper investigates the earthquake performance of concrete gravity dams under spatially variable seismic excitations. A nonlinear finite element model is developed and validated using shake table experimental results. The model is then subjected to spatially varying earthquake ground motions incorporating the wave passage effect, with values for apparent propagation velocities consistent with the source-site geometry and the shear wave velocity in the foundation rock. The evaluation reveals that different response patterns occur when spatially non-uniform and uniform seismic ground motions are applied as input excitations to the model, because spatially non-uniform excitations induce the quasi-static response, whereas uniform excitations do not, and, in addition, the dynamic response caused by different input motions varies. Notably, spatially non-uniform excitations produce larger opening at the heel of the dam and severer slipping at its toe; this latter observation can have a significant effect on the global equilibrium and stability of the dam during an earthquake.     

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。     

金沙江鲁地拉水电站混凝土重力坝地震抗滑稳定性的时程法分析

通过动力有限元时程法分析了金沙江鲁地拉水电站碾压混凝土重力坝在设计地震动作用下的动态响应,计算模型考虑了大坝–库水相互作用、大坝–岩基相互作用,用黏弹性吸波边界模拟了地震动能量向无限远域逸散的地基"辐射阻尼"效应。利用质点系"达朗贝尔原理"计算得到了坝体地震惯性力时程,通过将坝体惯性力时程极大值与振型分解反应谱法的惯性力计算值对比,验证了复杂地震动力数值计算结果的正确性。在坝体惯性力时程基础上叠加其它静力荷载,计算得到了大坝沿建基面的瞬态抗滑安全系数时程。计算结果表明:鲁地拉重力坝在设计地震动(0.36g)作用下的安全系数时程的极小值大于规范规定值,大坝整体抗震稳定性良好,不必采取提高整体抗滑稳定性的工程加固措施。作为典型重大工程实例研究,采用的动力计算方法对类似大坝工程的抗震计算具有参考意义。     

基于工程体与地质体相互作用的两体力学模型初探

针对大坝和坝基、坝肩和库岸相互作用传统的一体两介质模型,提出了两体力学模型的基本概念、研究思路以及应用范围;阐述了一体两介质力学模型与两体力学模型之间的差异,并用单轴压缩实验进行了验证;建立了重力坝和坝基相互作用的两体力学模型,为大坝与坝基的整体稳定性研究与评判提供了一条新的途径。     

基于强度折减法的重力坝深层抗滑加固措施研究

对于重力坝坝基存在软弱结构面的抗滑稳定处理,工程实践中常采用混凝土硐塞置换或预应力锚索方案。为分析比较两种方案的处理效果,采用有限元方法,建立包含基岩内软弱结构面的三维模型,采用Drucker-Prager强度准则,考虑自重荷载、水荷载、扬压力、坝前淤沙压力,研究某水电站工程溢流坝段坝基深层抗滑稳定问题。在采用重力坝设计规范计算抗滑处理后安全系数相同的条件下,采用有限元通过强度折减的方法可计算得到不处理、硐塞置换方案与锚索方案3种不同工况下的破坏形态,采用等效塑性应变超过某一幅值作为判断材料是否进入塑性状态的指标,结合坝体位移随强度折减系数的变化曲线,判断坝基是否出现滑动,分析结果表明硐塞置换方案较锚索方案的安全裕度更大。     

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.     

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。     

高面板堆石坝抗震安全评价标准与极限抗震能力研究

针对强震区高面板堆石坝的特点,提出了基于稳定、变形、面板防渗体系安全的高面板坝抗震安全评价和极限抗震能力分析方法,并建议了坝坡抗震稳定、坝体局部动力稳定、坝体地震残余变形、面板防渗体系的抗震安全评价标准。对坝高超过250 m的某高面板堆石坝进行了极限抗震能力分析,根据坝坡稳定性、地震残余变形、单元抗震安全性、面板防渗体系抗震安全性等多角度的评价结果,初步认为,该高面板堆石坝的极限抗震能力为0.50g~0.55g。     

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。     

Improved numerical method for time domain dynamic structure-foundation interaction analysis based on scaled boundary finite element method

Based on the reduced set of base function in scaled boundary finite element method (SBFEM), an improved time domain numerical approach for the dynamic structure-foundation interaction analysis was proposed. With reasonable choice of the number of base functions, the degrees of freedom on the structure-foundation interface were reduced and the associated computation for the calculation of convolution integral was greatly reduced. The results of this proposed approach applied to the calculation of a gravity dam and an arch dam. The acceleration frequency response functions were calculated and the influences affected by different reduced set of base functions as well as full set were compared. It was found that a higher degree of reduced set of base functions resulted in a significant increase of computational efficiency but a little bit of loss in accuracy. When the reduced set was decreased by 60%, the efficiency may be increased to up to five times, while the loss of accuracy of peak value of response will be less than 4%. It may be concluded that the proposed approach is suitable for large-scale structure-foundation interaction analysis.     

Reliability and variance-based sensitivity analysis of arch dams during construction and reservoir impoundment

The static performance of arch dams during construction and reservoir impoundment is assessed taking into account the effects of uncertainties presented in the model properties as well as the loading conditions. Dez arch dam is chosen as the case study; it is modeled along with its rock foundation using the finite element method considering the stage construction. Since previous studies concentrated on simplified models and approaches, comprehensive study of the arch dam model along with efficient and state-of-the-art uncertainty methods are incorporated in this investigation. The reliability method is performed to assess the safety level and the sensitivity analyses for identifying critical input factors and their interaction effects on the response of the dam. Global sensitivity analysis based on improved Latin hypercube sampling is employed in this study to indicate the influence of each random variable and their interaction on variance of the responses. Four levels of model advancement are considered for the dam-foundation system: 1) Monolithic dam without any joint founded on the homogeneous rock foundation, 2) monolithic dam founded on the inhomogeneous foundation including soft rock layers, 3) jointed dam including the peripheral and contraction joints founded on the homogeneous foundation, and 4) jointed dam founded on the inhomogeneous foundation. For each model, proper performance indices are defined through limit-state functions. In this manner, the effects of input parameters in each performance level of the dam are investigated. The outcome of this study is defining the importance of input factors in each stage and model based on the variance of the dam response. Moreover, the results of sampling are computed in order to assess the safety level of the dam in miscellaneous loading and modeling conditions.