Three‐dimensional numerical analysis of concrete‐faced rockfill dam using dual‐mortar finite element method with mixed tangential contact constraints

Concrete‐faced rockfill dam (CFRD) is a popular alternative to traditional dam types in the last two decades. The modelling of CFRD involves complex multi‐body contact and strong geometry and material nonlinearities. We present a numerical approach for the modelling of CFRDs in this paper. Based on the dual‐mortar finite element method, the presented approach considers different parts of rockfill and all concrete slabs as independent deformable continuum. The multi‐body contacts are modelled using Lagrange multipliers with a weak form segment‐to‐segment contact strategy. To alleviate instability induced by strong geometry nonlinearity in the slab–slab contact, we propose a mixed type of constraints for the tangential contact. A general transformation scheme is introduced to simplify the implementation of contact constraints. Three‐dimensional analysis of Tianshengqiao‐1 CFRD is performed. The nonlinear and time‐dependent deformation of the rockfill is considered. We study the influence of the rockfill deformation on the reliability of the concrete face. Three major concerns of the face, that is, the axial compression, the slab–slab separation and the face‐rockfill separation, are discussed in detail. The numerical results are compared with data from in‐situ observation. Copyright © 2016 John Wiley & Sons, Ltd.     

Structure analysis for concrete‐faced rockfill dams based on information entropy theory and finite element method

Numerical simulation methods are extensively used to analyze the stress and displacement of concrete‐faced rockfill dams (CFRD). The results of these methods are influenced by fuzzy factors, i.e. geometric features, material properties, loads and boundary conditions, which exist widely in the engineering of CFRD as a kind of commonly uncertain factor. To solve this problem, the information entropy theory and the conventional method of structure analysis, namely, finite element method (FEM), were combined in this work. Information entropy, as an effective tool of measuring uncertainty, was used to represent the uncertainty of CFRD. Based on the model that can transform fuzzy information entropy into random information entropy, fuzzy structure can be transformed into equivalent random structure, then mechanical characteristics of CFRD were analyzed by well‐developed stochastic FEM. As an example, one CFRD was chosen to analyze the structure, and the result shows that this method is effective. Copyright © 2011 John Wiley & Sons, Ltd.     

A dual mortar contact method for porous media and its application to clay-core rockfill dams

The clay-core rockfill dam is a multibody contact system in which the hydromechanical response of the clay core plays a crucial role. This complex problem is highly challenging to model numerically. We present a numerical approach that considers the multibody contact, consolidation, and strong geometric and material nonlinearities for the modeling of clay-core rockfill dams. Within the framework of the dual mortar finite element method, the presented approach considers the contact bodies as independent porous media continuums. The nonlinear contact conditions are derived based on the effective contact traction on contact interfaces and pore pressure continuity. The weak forms are obtained by introducing Lagrange multipliers as additional unknowns, which are then condensed through an extended general transformation. The presented method is first validated with a patch test considering the contact between two porous media. Then, a three-dimensional analysis of the Rumei clay-core rockfill dam is performed. The main numerical analysis concerns are the two observation galleries planned for construction inside the clay core. The galleries consist of dozens of tunnel-like concrete blocks, giving rise to complex concrete-concrete and concrete-clay contacts. The discontinuous separation and sliding between concrete blocks are investigated. For the concrete-concrete contact, both hard and soft joint approaches are evaluated and compared. The pore pressure results of the concrete structures are also analyzed.     

面板堆石坝垂直缝破坏下三维渗流场有限元模拟

采用改进节点虚流量法求解无压稳定渗流场,并引入无厚度的裂缝模型对破坏的垂直缝渗流行为进行模拟,得到面板堆石坝裂缝渗流问题的有限元分析方法,并编制Fortran程序。以某混凝土面板堆石坝为例,计算了面板单一垂直缝破坏和多条垂直缝破坏条件下的三维渗流场,得到不同条件下渗流场的水头分布、浸润线以及渗漏量,系统分析了面板堆石坝在垂直缝破坏条件下的稳定渗流场规律和特点。结果表明,该方法能对渗流逸出点和浸润线进行准确定位,还能很好地模拟面板垂直缝破坏对坝区渗流场的影响,可以为面板堆石坝的接缝设计提供参考。     

堆石体流变对混凝土面板坝应力变形特性的影响

简要介绍了公伯峡水电站混凝土面板堆石坝坝内堆石料流变试验结果和流变计算模型。采用三维有限单元法对公伯峡水电站混凝土面板坝进行了模拟计算,对比了考虑堆石料流变和不考虑流变的计算结果,分析研究了堆石料流变特性对坝体变形以及对混凝土面板应力变形和周边缝位移的影响。     

混凝土面板堆石坝中过渡区的渗流控制作用研究

在面板完好的条件下,面板堆石坝坝体的渗透稳定性很容易满足要求;在面板止水破损和面板失效的不利条件下,过渡区的渗流控制作用对于大坝的渗透稳定性具有关键意义。结合水布垭大坝实例,通过层间系数的分析,认为必须通过试验研究过渡料对垫层料的反滤保护作用。通过反滤试验研究了水布垭全级配过渡料对垫层料的反滤效果和渗透变形规律,结合已发表的研究成果进行综合分析,探讨了过渡区的渗流控制作用机制：过渡料与主堆石区一起,可对坝体起到很好的排水作用;在面板止水破损和面板失效的不利条件下,垫层料内部可能会发生颗粒迁移和内部结构调整,但在过渡料的反滤保护作用下可维持渗透稳定;初次遇到这种工况时,过渡区自身会有少量细粒流失,但其骨架将维持稳定,借助于主堆石区的支撑作用,过渡区将继续发挥其反滤和排水的双重作用。     

龙首二级面板堆石坝三维真非线性地震反应分析和评价

基于土石料三维粘弹塑性动力本构模型,并采用新型三维各向异性有厚度薄单元来模拟面板和堆石的接触面特性,建立了高面板堆石坝地震反应分析的三维真非线性动力分析方法.利用坝料动力特性的大型三轴试验成果,分析计算了龙首二级(西流水)面板堆石坝的地震反应,主要包括加速度反应、堆石体应力反应及坝体单元抗震安全系数、面板应力反应和变形及接缝位移、高趾墙动力反应等.为大坝的抗震设计提供了有力的技术依据.     

面板坝垂直缝及止水失效渗流场有限元模拟

以金川面板堆石坝为例,用有限元方法计算了当面板缝及止水局部失效时各种工况下的渗流场,系统分析了大坝在面板垂直缝及止水局部失效后的稳定渗流场的规律和特点。采用无厚度的二维平面单元来模拟面板垂直缝及止水结构周边缝,同时采用理论上严密的Signorini型变分不等式方法进行求解,此方法能对渗流出渗点和浸润线进行准确定位。通过分析计算结果,指出了面板缝及止水结构周边缝的失效位置,失效缝宽对等势线、浸润线以及渗漏量的影响。为面板堆石坝接缝的设计提供参考。     

水布垭面板堆石坝的三维弹塑性数值分析研究

在建的清江水布垭面板堆石坝高达233 m,是目前同类坝型中最高的.采用MSC.Marc非线性有限元程序,发展了三维子模型法,对该坝进行了三维弹塑性有限元仿真分析,模拟了面板的分缝、坝体材料分区、填筑及蓄水过程,采用双屈服面弹塑性模型模拟堆石体的变形特征.根据数值分析的结果,对坝体和面板的应力变形分布规律进行了探讨.     

茅坪溪沥青混凝土堆石坝填料参数反分析

茅坪溪沥青混凝土堆石坝是目前世界上最高的沥青混凝土心墙坝之一,由于上坝壳填料与设计料源有所改变,填料特性试验资料较少,有限元计算参数不准,很难客观评估大坝应力变形状态。根据大坝监测资料,采用Duncan-Chang E-? 模型和正算逆解逼近法进行参数反分析,比较客观准确地确定了坝体填料参数,计算结果与观测的实际规律或数值大小非常吻合,为蓄水期评价大坝的应力变形状态提供计算依据。     

Implementation of the finite element method in the three‐dimensional discontinuous deformation analysis (3D‐DDA)

A modified three‐dimensional discontinuous deformation analysis (3D‐DDA) method is derived using four‐noded tetrahedral elements to improve the accuracy of current 3D‐DDA algorithm in practical applications. The analysis program for the modified 3D‐DDA method is developed in a C++ environment and its accuracy is illustrated through comparisons with several analytical solutions that are available for selected problems. The predicted solutions for these problems using the modified 3D‐DDA approach all show satisfactory agreement with the corresponding analytical results. Results presented in this paper demonstrate that the modified 3D‐DDA method with discontinuous modeling capabilities offers a useful computational tool to determine stresses and deformations in practical problems involving fissured elastic media with reasonable accuracy. Copyright © 2008 John Wiley & Sons, Ltd.     

A computational framework to predict the water‐leakage pressure of segmental joints in underwater shield tunnels using an advanced finite element method

The construction of shield tunnels under riverbeds and seabeds has considerably increased over the past decades. Due to the ultra‐high water head, water leakage through tunnel joints is a major concern during a tunnel's service life. One practical solution to prevent groundwater penetration is to implement ethylene‐propylene‐diene‐monomer gaskets at the segmental joints. However, numerical simulation of fluid pressure penetration into rubber materials remains a challenging problem in computational mechanics. Severe mesh distortions can occur due to large deformation. Consequently, a convergent solution is difficult to achieve. This paper presents an Abaqus‐based numerical framework to solve the previously mentioned problem using the implicit finite element solver. The key aspects of this framework are twofold: (1) a remesh and re‐map algorithm to overcome the excessive mesh distortion, and (2) simulation of fluid penetration into the contact interface of the gaskets to reproduce the water‐leakage process at the tunnel joints. The proposed framework is first tested to simulate the gasket‐in‐groove mechanical behavior and is then validated using experimental data and the solution produced by an explicit finite element solver. The developed framework is then adopted to predict the water‐leakage pressure at gasketed tunnel joints to illustrate the practical applications. Finally, the numerical results are compared with experimental data to demonstrate the accuracy and robustness of the proposed method and confirm its superiority and effectiveness over existing methods. This novel method can be used by tunnel designers to analyze and estimate the waterproof behavior of gasketed joints in shield tunnels without performing extensive experimental testing works.