Refined mathematical model for the breaching of concrete-face sand-gravel dams due to overtopping failure

Overtopping is one of the main reasons for the breaching of concrete-face sand-gravel dams(CFSGDs).In this study,a refined mathematical model was established based on the characteristics of the overtopping breaching of CFSGDs.The model characteristics were as follows:(1)Based on the Renormailzation Group(RNG)k-εturbulence theory and volume of fluid(VOF)method,the turbulent characteristics of the dam-break flow were simulated,and the erosion surface of the water and soil was tracked;(2)In consideration of the influence of the change in the sediment content on the dam-break flow,the dam material transport equation,which could reflect the characteristics of particle settlement and entrainment motion,was used to simulate the erosion process of the sand gravels;(3)Based on the bending moment balance method,a failure equation of the concrete face slab under dead weight and water load was established.The proposed model was verified through a case study on the failure of the Gouhou CFSGD.The results showed that the proposed model could well simulate the erosion mode of the special vortex flow of the CFSGD scouring the support body of the concrete face slab inward and reflect the mutual coupling relationship between the dam-break flow,sand gravels,and concrete face slabs.Compared with the measured values,the relative errors of the peak discharge,final breach average width,dam breaching duration,and maximum failure length of the face slab calculated using the proposed model were all less than 12%,thus verifying the rationality of the model.The proposed model was demonstrated to perform better and provide more detailed results than three selected parametric models and three simplified mathematical models.The study results can aid in establishing the risk level and devising early warning strategies for CFSGDs.

Prediction of Concrete Faced Rock Fill Dams Settlements Using Genetic Programming Algorithm

In the present study a Genetic Programing model (GP) proposed for the prediction of relative crest settlement of concrete faced rock fill dams. To this end information of 30 large dams constructed in seven countries across the world is gathered with their reported settlements. The results showed that the GP model is able to estimate the dam settlement properly based on four properties, void ratio of dam’s body (e), height (H), vertical deformation modulus (Ev) and shape factor (Sc) of the dam. For verification of the model applicability, obtained results compared with other research methods such as Clements’s formula and the finite element model. The comparison showed that in all cases the GP model led to be more accurate than those of performed in literature. Also a proper compatibility between the GP model and the finite element model was perceived.

A simplified physically-based breach model for a high concrete-faced rockfill dam:A case study

A simplified physically-based model was developed to simulate the breaching process of the Gouhou concrete-faced rockfill dam （CFRD）, which is the only breach case of a high CFRD in the world. Considering the dam height, a hydraulic method was chosen to simulate the initial scour position on the downstream slope, with the steepening of the downstream slope taken into account; a headcut erosion formula was adopted to simulate the backward erosion as well. The moment equilibrium method was utilized to calculate the ultimate length of a concrete slab under its self-weight and water loads. The calculated results of the Gouhou CFRD breach case show that the proposed model provides reasonable peak breach flow, final breach width, and failure time, with relative errors less than 15% as compared with the measured data. Sensitivity studies show that the outputs of the proposed model are more or less sensitive to different parameters. Three typical parametric models were compared with the proposed model, and the comparison demonstrates that the proposed physically-based breach model performs better and provides more detailed results than the parametric models.

Seepage simulation of high concrete-faced rockfill dams based on generalized equivalent continuum model

This research focused on the three-dimensional(3 D) seepage field simulation of a high concrete-faced rockfill dam(CFRD) under complex hydraulic conditions. A generalized equivalent continuum model of fractured rock mass was used for equivalent continuous seepage field analysis based on the improved node virtual flow method. Using a high CFRD as an example, the generalized equivalent continuum range was determined, and a finite element model was established based on the terrain and geological conditions, as well as structural face characteristics of the dam area. The equivalent seepage coefficients of different material zones or positions in the dam foundation were calculated with the Snow model or inverse analysis. Then, the 3 D seepage field in the dam area was calculated under the normal water storage conditions, and the corresponding water head distribution, seepage flow, seepage gradient, and seepage characteristics in the dam area were analyzed. The results show that the generalized equivalent continuum model can effectively simulate overall seepage patterns of the CFRD under complex hydraulic conditions and provide a reference for seepage analysis of similar CFRDs.

Reservoir water effects on earthquake performance evaluation of Torul Concrete-Faced Rockfill Dam

This study presents earthquake performance analysis of the Torul Concrete-Faced Rockfill （CFR） Dam with two-dimensional dam-soil and dam-soil-reservoir finite element models. The Lagrangian approach was used with fluid elements to model impounded water. The interface elements were used to simulate the slippage between the concrete face slab and the rockfill. The horizontal component of the 1992 Erzincan earthquake, with a peak ground acceleration of 0.515g, was considered in time-history analysis. The Drucker-Prager model was preferred in nonlinear analysis of the concrete slab, rockfill and foundation soil. The maximum principal stresses and the maximum displacements in two opposite directions were compared by the height of the concrete slab according to linear time-history analysis to reveal the effect of reservoir water. The changes of critical displacements and principal stresses with time are also shown in this paper. According to linear and nonlinear time-history analysis, the effect of the reservoir water on the earthquake performance of the Torul CFR Dam was investigated and the possible damage situation was examined. The results show that the hydrodynamic pressure of reservoir water leads to an increase in the maximum displacements and principal stresses of the dam and reduces the earthquake performance of the dam. Although the linear time-history analysis demonstrates that the earthquake causes a momentous damage to the concrete slab of the Torul CFR Dam, the nonlinear time-history analysis shows that no evident damage occurs in either reservoir case.

Numerical simulation of seismic damage and cracking of concrete slabs of high concrete face rockfill dams

Based on the damage constitutive model for concrete, the Weibull distribution function was used to characterize the random distribution of the mechanical properties of materials by finely subdividing concrete slab elements, and a concrete random mesoscopic damage model was established. The seismic response of a 100-m high concrete face rockfill dam(CFRD), subjected to ground motion with different intensities, was simulated with the three-dimensional finite element method(FEM), with emphasis on exploration of damage and the cracking process of concrete slabs during earthquakes as well as analysis of dynamic damage and cracking characteristics during strong earthquakes. The calculated results show that the number of damaged and cracking elements on concrete slabs grows with the duration of earthquakes. With increasing earthquake intensity, the damaged zone and cracking zone on concrete slabs grow wider. During a 7.0-magnitude earthquake, the stress level of concrete slabs is low for the CFRD, and there is almost no damage or slight damage to the slabs. While during a 9.0-magnitude strong earthquake, the percentages of damaged elements and macrocracking elements continuously ascend with the duration of the earthquake, peaking at approximately 26% and 5% at the end of the earthquake, respectively. The concrete random mesoscopic damage model can depict the entire process of sprouting, growing, connecting, and expanding of cracks on a concrete slab during earthquakes.

Seismic responses of high concrete face rockfill dams:A case study

Seismic responses of the Zipingpu concrete face rockfill dam were analyzed using the finite element method. The dynamic behavior of rockfill materials was modeled with a viscoelastic model and an empirical permanent strain model. The relevant parameters were obtained either by back analysis using the field observations or by reference to parameters of similar rockfill materials. The acceleration responses of the dam,the distribution of earthquake-induced settlement, and the gap propagation under the concrete slabs caused by the settlement of the dam were analyzed and compared with site investigations or relevant studies. The mechanism of failure of horizontal construction joints was also analyzed based on numerical results and site observations. Numerical results show that the input accelerations were considerably amplified near the top of the dam, and the strong shaking resulted in considerable settlement of the rockfill materials, with a maximum value exceeding 90 cm at the crest.As a result of the settlement of rockfill materials, the third-stage concrete slabs were separated from the cushion layer. The rotation of the cantilever slabs about the contacting regions, under the combined action of gravity and seismic inertial forces, led to the failure of the construction joints and tensile cracks appeared above the construction joints. The effectiveness and limitations of the so-called equivalent linear method are also discussed.

Dynamic response of concrete face rockfill dam affected by polarity reversal of near-fault earthquake

In China,an increasing number of high concrete face rockfill dams(CFRDs)are located in high intensity earthquake zones,some of which are close to the seismic fault line.Recordings suggest that near-fault ground motions are characterized by large one-sided velocity pulses.The conventional dynamic analysis of dams,however,neglects the features of strong ground movements.In this study,under different ground motion levels some numerical dynamic studies considering the one-sided broadband pulses of near-fault earthquakes are presented for CFRDs based on a generalized plasticity model for rockfill materials.The results indicate that the displacements of dam crest corresponding to positive and reverse input of near-fault ground motion make a significant difference,while the displacements of the dam crest under artificial seismic waves are similar.Furthermore,using the horizontal and vertical components as simultaneous excitations near the faults,the displacements of the dam crest before and after reversing the motion produce a larger difference than that using a single component.More importantly,the difference of horizontal displacements of the dam crest caused by polarity reversal of near-fault ground motions increases with the increase of earthquake intensity.Due to the randomness and uncertainties of earthquakes,using a stochastic near-field motion input as excitation without considering the polarity(i.e.,positive vs reversed waveform),does not necessarily obtain a conservative result.

Fuzzy Earthwork Dynamic Allocation and Optimization for Construction of High Concrete Face Rockfill Dam

Due to the complexity of earthwork allocation system for the construction of high concrete face rockfill dam,traditional allocation and planning are not able to function properly in the construction process with strong randomness.In this paper,the working mechanism of earthwork dynamic allocation system is analyzed comprehensively and a solution to fuzzy earthwork dynamic allocation is proposed on the basis of uncertain factors in the earthwork allocation of a hydropower project.Under the premise of actual situation and the experience of the construction site,an all-coefficient-fuzzy linear programming mathematical model with fuzzy parameters and constraints for earthwork allocation is established according to the structure unit weighted ranking criteria.In this way,the deficiency of certain allocation model can be overcome.The application results indicate that the proposed method is more rational compared with traditional earthwork allocation.

The Deformation and Stress Analysis of Na Ba Reservoir Concrete Face Rock-Fill Dam

Based on the APDL （ANSYS Parametric Design Language） and combined with the actual project related to parameters of filling material, imported Duncan-Chang constitutive model which has been widely applied in soil mass and rock-fill in the ANSYS software. With the three-dimensional nonlinear finite element analysis by the mid-point incremental method, what have been computed are the deformation and stress analysis ofNa Ba reservoir CFRD （Concrete Face Rock-fill Dam） in filling period. The calculation results provide practical reference for the dam during construction safety filling stress and deformation analysis and real-time monitoring.

A CHANGED FACE OF GUANGZHOU TRADE FAIR

FAMOUS-BRAND PRODUCTS ARE WARMLY WELCOMEUPGRADING TECHNOLOGIES ARE HIGHLY CHERISHEDEXQUISITE FINE-ART PRODUCTS RECEIVE SPECIAL ATTENTION.

大直径盾构管片清水混凝土制备及施工关键技术研究

以江阴靖江长江隧道工程为依托,从混凝土工作性能、力学性能及表观质量等方面开展大直径盾构管片清水混凝土配制技术研究,并在混凝土原材料、浇筑、养护等方面提出了施工关键控制技术。结果表明,研制的管片清水混凝土具有优异的表观性能与抗裂性能,辅以优化的关键施工工艺,显著改善了管片表观质量,可为同类工程的质量控制提供参考。

超深覆盖层上面板坝防渗墙连接板接缝变形机制及优化分析

针对超深软弱覆盖层上的面板坝工程止水缝安全问题,从变形和应力2个方面开展优化研究,揭示了防渗墙连接板趾板面板防渗体系的变形模式,定位了薄弱位置,提出了优化方案,并量化了工程应用效果.结果表明,防渗墙与趾板间沉降差集中在防渗墙与连接板之间的止水缝处,设置多块连接板无法起到逐步过渡沉降差的作用.防渗墙下游侧设置侧向支撑、制作倾斜形止水缝、趾板下设支撑墙均可减小防渗墙连接板间止水缝沉陷变形.相比垂直止水缝和多块连接板的传统方案,所提的防渗墙顶部拓宽连接板倾斜形止水缝以及防渗墙顶部拓宽倾斜形止水缝趾板下设支撑墙的深厚覆盖层上面板坝防渗体系综合优化方案可使防渗墙与连接板之间止水缝沉陷变形分别减小41.5%和53.8%.

碳纳米管改善面板混凝土早龄期变形研究

在水利工程中大体积混凝土开裂问题普遍存在,而早龄期变形是大体积混凝土早龄期开裂的主要驱动力。为了研究碳纳米管(CNTs)对面板混凝土(FSC)早龄期变形的影响,采用温度—应力试验,研究两种温度养护历程下基准面板混凝土和掺入CNTs面板混凝土的应力与应变发展规律。基于成熟度理论,分离出早龄期温度变形与徐变,得到FSC早龄期时变热膨胀系数与徐变度发展曲线。试验结果表明:相较于基准组,CNTs的掺入可以减少FSC早龄期自收缩,降低早龄期热膨胀系数,从而减少温度变形,增加早龄期拉伸徐变度,可以有效改善FSC早龄期变形,降低FSC早龄期开裂风险。

堆石料本构模型对混凝土面板坝应力变形计算结果的影响研究

堆石料本构模型选择是影响混凝土面板坝应力变形计算结果的主要因素。以某典型面板坝为例,采用邓肯E-B非线性弹性模型和“南水”双屈服面弹塑性模型,对坝体填筑过程和蓄水过程进行了三维有限元模拟;研究了两种模型计算的坝体和面板的位移和应力分布差异;分析了两种模型计算结果呈现差异的原因。两种模型计算结果最显著的差异体现在两个方面:(1)“南水”模型计算的坝体沉降、面板挠度等位移指标小于E-B模型,其原因是“南水”模型计算的坝体小主应力和变形模量更高。(2)E-B模型计算结果显示蓄水后面板底部顺坡向受拉;而“南水”模型计算的面板顺坡向应力为全断面受压。前者是由E-B模型的各向同性弹性本质决定的,垫层料因水压力作用顺坡向膨胀,产生沿坡面向上的位移;后者是其F1屈服面持续扩张产生塑性体积收缩导致的,塑性体缩抵消了顺坡向弹性膨胀,使垫层料产生沿坡面向下的位移。

250 m级特高面板堆石坝混凝土面板顺坡向应力控制措施研究

面板应力变形控制是建设250 m级特高混凝土面板堆石坝的关键难题.大量工程实测案例和研究计算表明,特高面板坝压应力常处于较高水平,对于坝轴向应力来说,采用柔性缝降低压应力措施已被工程界普遍接受,然而,目前对于如何降低面板顺坡向压应力尚缺少有效的解决方法.本文以拟建的240 m级GS面板坝为研究对象,从特殊增模区布置、面板施工顺序、面板低高程柔性横缝、高压力区高强度混凝土材料等4个方面提出改善面板顺坡向应力的工程措施.文中通过三维有限元精细模拟方法分析了提出的顺坡向应力改善措施的效果,文中提出的措施可为250 m面板堆石坝面板应力控制提供借鉴.

高纬度高寒区面板堆石坝防渗面板修复方案及经验

JLBLK水电站大坝是建于高纬度高寒区的百米级全断面堆石面板坝,最大坝高140.3 m。通过降水处理,现场发现18^(#)、19^(#)面板挤压破损程度严重且有加剧趋势,25^(#)、26^(#)、27^(#)面板断裂。经与国内外同类工程比较,水库渗漏量总体偏大,变形量偏大,且尚未收敛,三维流变反演成果表明后期尚有17%的沉降量。为保证修复效果满足后期变形和渗透稳定需要,针对18^(#)、19^(#)面板水上破损区采用高于原设计强度混凝土分小区进行补强,并结合工程特点和设计方案提出适合本工程的修复施工方案,修复后面板各项指标均满足要求。

混凝土面板与堆石料接触面模型及其应用

混凝土面板是面板坝防渗安全的生命线,其应力变形特性主要取决于坝体堆石料的应力变形特性及面板与堆石料之间的接触特性。在面板坝的应力变形计算中,通常采用接触面模型模拟面板与堆石料之间的荷载传递机制,因此接触面模型是否合理,直接影响到面板应力变形计算结果的可靠性。分析了传统双曲线接触面模型存在的不足,提出了一个考虑双向剪切耦合效应,且符合强度准则和标架无差异原则的接触面本构模型,该模型参数少,数值实现方便,可以定性地模拟出实际面板坝工程中出现的混凝土挤压破坏区域。

综放面采空区漏风规律及防治技术研究

综放工作面采空区漏风易导致遗煤自燃,危及矿井安全。以大南湖一矿1305综放工作面为研究背景,采用数值模拟和现场试验的方法,研究了综放工作面采空区漏风规律,提出了综放工作面端头封堵采空区防漏风技术方案,并在现场进行了试验。结果表明,工作面端头是综放工作面采空区漏风的主要通道,其中进风巷侧端头漏风率达19%;风流在采空区内渗透深度约160 m;工作面端头封堵后,风流在采空区内渗透深度缩减至100 m左右;1305综放工作面端头封堵后,采空区漏风率降低17个百分点。

工业遗产项目锈红色清水混凝土结构施工关键技术研究

通过大运河杭钢工业旧址综合保护项目中锈红色清水混凝土新建结构的实施,对其关键施工技术进行了研究总结。从材料配制与施工管理2个角度,对锈红色清水混凝土的观感控制技术进行了总结;针对竖向结构施工,从普通竖向结构以及具有设计特色的多边形柱、少拼缝清水柱等方面进行了控制要点的总结;针对锈红色水平结构施工,涵盖了普通水平结构、双层空腔楼板及楼梯结构等方面的施工经验总结。该项目的新建混凝土结构设计独特,得益于团队的创新研发,确保了项目实施效果。