3D analysis of the 174-m high Quxue asphalt-core rockfill dam in a narrow canyon

The site for the high Quxue Dam has a narrow canyon with very steep abutments and complex geology in Sichuan Province, China. Various types of embankment and concrete dams were considered and an asphalt-core embankment dam (ACED), 174 m high, was selected. The asphalt core is a slender impervious element in an embankment dam and some concerns have been raised about the reliability and safety of the asphalt-core type of dams (ACEDs). This paper presents the case study of the highest asphalt core dam ever built and presents measured and numerical analyses of the core deformations. A 3D non-linear FE analysis has been performed for the Quxue Dam, and the results have been compared with those computed by a 2D analysis to study the effects of the narrow canyon. The computed results are compared with the monitoring data from dam construction and first impoundment. The maximum settlement measured inside the embankment during construction was only about 0.7 m due to the good basaltic rockfill used and the heavy compaction in layers of only 1.0 – 1.2 m thickness. The results of the 3D analysis agree well with the measured downstream displacements and the deflected shape of the thin asphalt core during impoundment, while the 2D analysis overpredicted the maximum displacement by a factor of about two. At a reservoir level 3 m below full supply level, the maximum measured downstream core displacement was only about 80 mm due to the stiff rockfill and the restraining effects of the abutments in the narrow valley.The rockfill behaviour was modelled by the constitutive relationship proposed by Duncan and Chang (1970). The rockfill parameters were determined by laboratory tests prior to construction and were adjusted to better match field observations of vertical settlements during construction. As asphalt concrete exhibits pronounced visco-elastoplastic behaviour, the material modelling was based on long-term triaxial creep tests on samples drilled out of the dam core. The performance monitoring and numerical analysis results for the record-high Quxue ACED document that the concerns expressed about the asphalt core safety and behaviour is not warranted. The asphalt core type of dam is suitable even for high ACEDs in narrow valleys with steep abutments.     

高混凝土面板堆石坝地震损伤机理研究

以紫坪铺面板堆石坝为例,基于堆石料的黏弹性模型和地震残余应变模型计算分析了高混凝土面板堆石坝的地震响应,并结合震害调查结果分析了高混凝土面板堆石坝的地震损伤机理。研究表明,输入地震加速度在坝顶附近和坝坡表面显著放大,呈现出显著的鞭梢效应,导致坝顶和下游坝坡上部堆石体松动滚落。地震导致大坝堆石体产生显著剪缩,坝体断面整体向内收缩,刚性混凝土面板与垫层料之间脱空,脱空后面板与垫层料之间的摩擦力大幅减小甚至消失,面板在自重和地震惯性力联合作用下向下滑动,致使面板水平施工缝发生错台,面板表面产生裂缝。地震还导致岸坡附近左右坝段堆石体向河谷中央位移,致使岸坡附近面板垂直接缝发生拉伸破坏,河床中部垂直接缝及附近混凝土面板发生挤压破坏。数值计算和震害调查结果均表明,高混凝土面板堆石坝的地震损伤现象主要与其堆石体地震残余变过大,以及堆石体与防渗系统之间变形不协调密切相关,故强震区修建高面板坝应尽可能提高堆石体压实密度,以减小坝体的地震残余变形。     

三峡茅坪溪高沥青混凝土心墙堆石坝运行性状研究

茅坪溪防护坝是三峡工程的副坝,也是目前中国最高的沥青混凝土心墙坝.分析该坝在三峡库水位135 m时的变形规律,据此对坝体填料的参数进行反分析.在此基础上对设计水位175 m时及不同水位下,高沥青混凝土心墙的应力与变形进行非线性有限元数值仿真,并研究沥青混凝土参数取值对心墙运行性状的影响.采用双曲函数与幂函数结合的模式拟合沥青混凝土的三轴蠕变试验曲线,对大坝进行蠕变分析.分析结果表明,考虑蠕变效应,心墙的水平变形与最大主应力将有较大的增加.研究结果同时也表明,不同蓄水过程对心墙性状的影响不大,心墙产生水力劈裂、剪切破坏与挠曲破坏的可能性不大.研究结果可供大坝蓄水计划参考,并为高水头下高沥青混凝土心墙坝的运行提供一定的参考.     

两向地震波作用下沥青心墙坝受力研究

地震荷载对沥青混凝土心墙坝体结构力学性能的影响是尤为突出的。本文利用势流体理论模拟水位对大坝的压力作用,并且在两向地震荷载作用下提取堤坝的位移、加速度和应力。受力分析表明：在两向地震波作用下大坝的位移、加速度和应力均有明显增加,最大位移和应力均发生在沥青心墙的中部,产生了地震沉降,心墙中部位置是受力薄弱环节,需要加固处理。     

Cyclic Triaxial Tests on Asphalt Concrete as a Water Barrier for Embankment Dams

The seismic behavior of asphaltic concrete used in embankment dams subjected earthquake loads has been studied. In order to evaluate the dynamic behavior, an extensive series of monotonic and cyclic tests were carried out on triaxial specimens of asphalt concrete used in hydraulic structures. The MTS-dynamic equipment at the Norwegian Geotechnical Institute (NGI) was used for this purpose. Temperature and frequency effects on specimen behavior and on specimen degradation have been studied under the cyclic loads in both isotropic and anisotropic initial stress conditions. For investigation of the fatigue behavior, thousands of cyclic loads were imposed on some of the specimens. Moreover, to study any sign of material degradation due to the cyclic loading, the post-cyclic monotonic stress-strain curve was compared with the corresponding curve for specimens that were not first subjected to cyclic loading. Geotechnical parameters to be used in dynamic numerical analysis models are also presented.     

Seismic performance and numerical simulation of earth-fill dam with geosynthetic clay liner in shaking table test

In this paper, shaking table tests were carried out on both a small-scale and a full-scale earth-fill dams with geosynthetic clay liners to examine their seismic performance. The behavior of these fully instrumented earth-fill dams when subjected to seismic loading was also simulated by numerical analysis. Firstly, in the small-scale shaking table test, no failure was observed along the geosynthetic clay liner when the earth-fill dam was subjected to seismic motion. Numerical analysis confirmed that the behavior of the model earth-fill dam was unaffected by the geosynthetic clay liner. Secondly, a comparative shaking table test was carried out on full-scale earth-fill dams, one with a sloping core zone and another with a geosynthetic clay liner. Both model dams showed similar acceleration response and deformation behavior. It should be mentioned that the acceleration response increased gradually toward the top of the dam, and the deformation, after shaking, was relatively large near the foot of the slope. These observations were successfully simulated by the numerical analysis.     

Detail design,building and commissioning of tall building structural models for experimental shaking table tests

In the areas of seismic engineering, shaking table tests are powerful methods for assessing the seismic capacity of buildings. Since the size and capacity of existing shaking tables are limited, using scale structural models seems to be necessary. In recent years, many experimental studies have been performed using shaking table tests to determine seismic response of structural models subjected to various earthquake records. However, none of the past research works discussed practical procedure for creating the physical model. Therefore, in this study, a comprehensive procedure for design, building and commissioning of scale tall building structural models has been developed and presented for practical applications in shaking table test programmes. To validate the structural model, shaking table tests and numerical time history dynamic analyses were performed under the influence of different scaled earthquake acceleration records. Comparing the numerical predictions and experimental values of maximum lateral displacements, it became apparent that the numerical predictions and laboratory measurements are in a good agreement. As a result, the scale structural model can replicate the behaviour of real tall buildings with acceptable accuracy. It is concluded that the physical model is a valid and qualified model that can be employed for experimental shaking table tests. Copyright © 2015 John Wiley & Sons, Ltd.     

基于变形控制标准的高土石坝地震可靠度分析

基于可靠度分析的设计方法是科学定量地研究和保证岩土工程安全性的重要手段之一。通过定量考察土石坝工程中的不确定性因素,综合评估地震失效概率,可为高土石坝抗震设计和风险评估提供参考。以坝顶震陷率作为地震安全控制指标,提出了同时考虑地震和筑坝料参数不确定性的高土石坝地震可靠度分析方法。首先,采用地震烈度作为地震危险性的宏观衡量尺度,通过引入地震烈度概率模型,将基于概率烈度的地震动峰值作为地震强度因子,调整规范谱人工地震波的幅值进行动力有限元计算。然后,采用适用于处理小样本和非线性问题的高斯过程响应面法,建立筑坝料参数与坝顶震陷率之间的非线性映射关系,结合蒙特卡罗法计算高土石坝地震失效概率。最后,以紫坪铺面板堆石坝为例,应用该方法考察了设计基准期内的地震失效概率。     

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。     

高沥青混凝土心墙受拉特性的简化力学分析方法

目前,沥青混凝土心墙受力变形特性研究尚缺乏简化的分析方法。针对高沥青混凝土心墙存在严重的受拉现象,探讨了心墙产生拉应力的机理,结合拱结构的特殊传力机制,提出了减小心墙拉应力的构想,即将直线型心墙堆石坝设计成曲线型心墙堆石坝;基于Winkler弹性地基直梁和曲梁理论,构建了直线型心墙和曲线型心墙的简化力学分析模型;借助该模型分析了坝高和堆石料模量对直线型心墙的挠曲变形和拉应力(弯矩)的影响,考察了曲线型心墙减小其内部拉应力的效果。研究表明,建立的简化力学分析模型能够较好地反映心墙的受力变形特性;直线型心墙端部存在较大的拉应力,坝高越高和堆石料模量越小,心墙端部的拉应力越大,心墙产生拉破坏的风险越大;曲线型心墙借助挠曲变形使其轴线缩短和将横向荷载部分转化成轴向压荷载以减小弯矩以及增大轴向压力达到减小其端部拉应力的目的,曲线型心墙相较于直线型心墙拉应力减小约42.7%,显著改善了心墙的受拉特性,增强了心墙的安全性。     

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。     

基于堆石体二元介质模型的面板坝数值计算

 对于高面板堆石坝而言,在高应力场作用下堆石颗粒破碎明显,从而导致坝体变形率增加,因此在数值计算中必须考虑颗粒破碎的影响,传统的堆石体本构模型由于不能合理反映颗粒破碎的影响,导致计算变形与实测变形差别较大。天生桥面板堆石坝为我国已建工程中同类坝型的第一座200 m级高坝,具有丰富的原型观测资料,在基于考虑堆石体颗粒破碎的二元介质模型的基础上,采用平面有限元分析坝体的应力变形性状,并与实测结果进行了对比分析,结果表明：考虑颗粒破碎后,坝料的剪胀量将会减小,剪缩量相应增大,建议模型的计算结果定性上更加精确,定量上也更为合理,可以更好地反映面板坝尤其是高面板坝的应力变形特性。     

水布垭面板堆石坝应力变形监测资料分析

土的本构关系、土与结构物相互作用机理、土工数值分析方法始终是土力学研究的核心问题,高面板堆石坝作为一个典型的土工构筑物,其应力变形实测成果对于研究上述问题是非常有意义的。依据水布垭面板堆石坝的监测资料,对高面板堆石坝的坝体变形、面板应力及面板缝的变形进行了系统分析,为堆石料本构模型的研究、堆石坝的应力变形数值分析及设计提供参考。     

高心墙堆石坝坝基廊道受力特性研究

在中国水资源最为丰富的西部地区,河床覆盖层厚达数十米甚至百米,一大批土石坝正在和将在这些大江大河上建设。坝体心墙与坝基防渗墙多采用廊道这种结构型式进行连接,廊道受力条件复杂,是工程成败的关键,但是有些已建工程却出现了廊道漏水的现象,廊道开裂和结构缝破坏成为亟待解决的问题。为了对廊道受力情况和开裂规律有一个清楚的认识,分析总结了几个工程廊道的监测资料,同时基于混凝土非线性本构理论,建立有限元模型对廊道进行了数值模拟。对监测结果和数值计算结果进行对比分析之后,探讨了廊道中的结构缝问题和廊道整体的受力规律,指明了廊道中需要重点关注的易开裂部位,为廊道合理配筋提供了指导,同时为类似工程的决策提供参考。     

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。     

金佛山沥青混凝土心墙坝二维渗流计算分析

渗透水流将会对土石坝的坝体以及坝基渗透破坏产生巨大的危害性。本文依托金佛山水电站工程,根据沥青混凝土心墙堆石坝方案的地质条件及渗流控制特点,建立了平面有限元计算分析模型,模拟了坝体和坝基在不同水位组合条件下的渗流场,重点研究了其渗透破坏的可能性,并且对防渗帷幕和坝基渗透系数的敏感性进行了分析。计算分析结果表明:各种水位组合下,沥青混凝土心墙及防渗帷幕起主要的阻水作用,防渗帷幕的水力比降较大,其安全稳定性需要重视。渗流场分布对防渗帷幕及坝基渗透系数不敏感,而渗流流量相对敏感。     

茅坪溪土石坝沥青混凝土心墙的力学特性与施工控制

茅坪溪土石坝是三峡工程的重要组成部分,与三峡大坝同属1等1级永久建筑物,该坝的特色是采用了展压式沥青混凝土心墙防渗系统。在大量的试验研究、数值计算和施工技术研究的基础上,综合分析了沥青混凝土心墙所特有的力学性质,提出了严格控制心墙的力学参数变化,从而确保工程质量的施工控制方法。     

Centrifuge Model Tests of a Rockfill Dam and Simulation Using Consolidation Analysis Method

A series of centrifuge model tests for a typical rockfill dam (central core zone type) was conducted in order to investigate behaviour of the dam due to cycles of reservoir water levels. The dam models consisted of comparatively well-compacted core zone and loosely compacted rock zone. A typical result among the model tests was also simulated by using a consolidation analysis method coupled with an elastoplastic model for unsaturated geo-materials. The main behaviour seen from the centrifuge tests was that large amounts of settlements due to wetting within the upstream rock zone were monitored; the crest of the dam at first moved toward upstream and then returned toward downstream in the first reservoir filling; and cracks along the dam axis were observed on the upper parts of the upstream and downstream slopes. A typical result of the dam model tests during reservoir filling was simulated. The simulation results showed that the settlements calculated agreed mostly with those measured; the settlements due to wetting could also be estimated within the upstream rock zone; the horizontal displacements toward upstream increased with the cycles of up-and-down water levels and they concentrated to a shallow region near the upstream surface; tension stresses were calculated at the places where the cracks were monitored in the model tests; and just after construction, arching actions in both the vertical and horizontal effective stress distributions could be seen on both the upstream and downstream boundaries between the core and rock zones but the arching action on the upstream boundary disappeared with water levels going up. The simulation method presented here provided an effective approach to analyze the behaviour of the rockfill dam during reservoir filling periods.     

全库铺设沥青混凝土面板水库的抗震设计

介绍在建中日本最大规模的全库铺设沥青混凝土面板水库的抗震设计。基于水库所处的地形、地质及堤体填筑条件，酋先对水库整体进行三维有限元动力分析，从总体上掌握水库的地震反应特性；然后对变形较大的断面进行详细的二维动力分析，获得面板的最大动应变。同时，通过大量室内试验，确定满足施工要求的沥青混凝土配合比及其物理力学特性。根据面板的材料特性及其构造特点，提出二级抗震设防的极限状态设计法，并对该水库面板的抗震性能进行校核。     

寺坪坝坝体材料特性及坝型适应性研究

在湖北保康县寺坪水电枢纽工程可行性研究和设计阶段,按照坝基岩体条件以及为充分利用当地天然材料,选择黏土心墙坝和面板堆石坝进行可行性研究和方案比较。为研究坝体材料的适用性以及坝体应力应变状态,对当地黏土防渗料、砂砾石和页岩料的物理力学性质进行了全面的试验研究,对坝体渗流和应力应变有限元状态进行了有限元分析。本文简要介绍试验研究和数值分析的成果,对坝体填料的物理力学性质、坝体应力应变状态和坝型选择问题进行分析和总结。