Fluid solid coupling model based on endochronic damage for roller compacted concrete dam

According to the characteristics of thin-layer rolling and pouring construction technology and the complicated mechanical behavior of the roller compacted concrete dam(RCCD)construction interface,a constitutive model of endochronic damage was established based on the endochronic theory and damage mechanics.The proposed model abandons the traditional concept of elastic-plastic yield surface and can better reflect the real behavior of rolled control concrete.Basic equations were proposed for the fluid solid coupling analysis,and the relationships among the corresponding key physical parameters were also put forward.One three-dimensional finite element method(FEM)program was obtained by studying the FEM type of the seepage-stress coupling intersection of the RCCD.The method was applied to an actual project,and the results show that the fluid solid interaction influences dam deformation and dam abutment stability,which is in accordance with practice.Therefore,this model provides a new method for revealing the mechanical behavior of RCCD under the coupling field.

Influence of construction interfaces on dynamic characteristics of roller compacted concrete dams

To study the influence of construction interfaces on dynamic characteristics of roller compacted concrete dams(RCCDs),mechanical properties of construction interfaces are firstly analyzed. Then, the viscous-spring artificial boundary(VSAB) is adopted to simulate the radiation damping of their infinite foundations, and based on the Marc software, a simplified seismic motion input method is presented by the equivalent nodal loads. Finally, based on the practical engineering of a RCC gravity dam, effects of radiation damping and construction interfaces on the dynamic characteristics of dams are investigated in detail. Analysis results show that dynamic response of the RCC gravity dam significantly reduces about 25% when the radiation damping of infinite foundation is considered. Hot interfaces and the normal cold interfaces have little influence on the dynamic response of the RCC gravity dam.However, nonlinear fracture along the cold interfaces at the dam heel will occur under the designed earthquake if the cold interfaces are combined poorly. Therefore, to avoid the fractures along the construction interfaces under the potential super earthquakes,combination quality of the RCC layers should be significantly ensured.

Auto Identification of Rolling Layers in Roller-Compacted Concrete Dam

A scheme for identifying rolling layers in roller-compacted concrete (RCC) dam automatically was presented. First, a conceptual model was developed. Second, by using a computational geometry method, the auto identification of rolling layers and auto matching between rolling compaction machines and rolling layers were realized based on spatial control points. An application to the construction of Guandi RCC dam showed that the auto identification of rolling layers played an important role in ensuring the engineering quality.

Vibration sensitive admixture for roller compacted concrete

In order to further speed up the construction progress,shorten the rolling time and reduce the rolling times of roller compacted concrete after analyzing work of construction progress improvement measures of roller compacted concrete,research on vibration sensitive admixture is carried out and satisfactory results are acquired.The new type vibration sensitive admixture was used in the project of Jinghong hydropower station in Yunnan Province,China.The engineering experimental results show that various indexes have been verified.Meanwhile,the compactness of roller compacted concrete is improved under the same rolling times,the rolling times and the duration time can be reduced under the same compactness requirement in construction practice.

Intelligent compaction theory of high roller compacted concrete dam

The concept and realization process of intelligent compaction for the construction of high roller compacted concrete dam were presented,as well as the theory of monitoring and intelligent feedback control.Based on the real-time analysis of the compaction index,a multiple regression model of the dam compactness was established and a real-time estimation method of compaction quality for the entire work area of roller compacted concrete dam was proposed finally.The adaptive adjustment of the rolling process parameters was achieved,with the speed,the exciting force,the roller pass and the compaction thickness meeting the standards during the whole construction process.As a result,the compaction quality and construction efficiency can be improved.The research provides a new way for the construction quality control of roller compacted concrete dam.

Seepage Mitigation in Hydropower Dams by Optimization in Roller Compacted Concrete Interlayer (Monoliths) Joint Bonding Technology

Roller Compacted Concrete (RCC) has gained favorable recognition in hydropower and water resource dam construction. With optimization in construction technology and materials used for RCC Dams, cost is no longer a major disadvantage as compared to environmental impact, that is, wildlife habitat disruption. In as much as it has become optimal for investment in hydropower dam construction, the scourge for dam failure is still eminent, which is as a result of excessive seepage compromising the integrity of the mechanical properties of the dam. The aim of the paper is to highlight successful application methods in joint bonding to avoid excessive seepage and reduce the autogenous healing to a few years of operation. In view of optimization, this paper presents a comprehensive study on the influences of interlayer joints bonding quality from RCC mix performances and how it consolidates the RCC layers to withstand the shear strength along the interface, especially on the high dams. The case study is the RCC dam at the 750 MW Kafue Gorge Lower Hydropower Station. The scope of the study reviews the joint type judged by Modified Maturity Factor (MMF) with joint surface long time exposed in regions with dry and high temperature, technical measures of layer bonding quality control under condition of long time joint surface exposure, effects of joints shear strength and impermeability of the RCC layers when under the conditions of plastic and elasticity. The subtle observations made during the dam construction phases were with respect to the optimal use of materials in relation to RCC mix designs and the basis for equipment calibration for monitoring important data that can be referenced during analysis of shear forces acting on the RCC dam over time.

Effects of Wood Ash on Properties of Concrete and Flowable Fill

This research investigated the use of wood ash to partially replace cement or sand in conventional concrete, roller compacted concrete (RCC), and flowable fill. The main focus was to determine how the wood ash addition affected the main fresh and hardened properties of these materials. It was found that the wood ash could be successfully incorporated into the conventional concrete. In particular, the wood ash addition not only accelerated the setting, but also improved the early and the 28-day compressive strength of concrete that contained the blast furnace slag. It was also observed that the wood ash could be positively added into RCC to facilitate the compaction and reduce the risk of segregation. In addition, the wood ash can be beneficially introduced into the flowable fill mixtures to facilitate flow, to alleviate bleeding and subsidence, as well as to achieve controlled strength especially when combined with the class C or the class F fly ash.

Back analysis of mechanical parameters of roller compacted concrete dam

In view of the diversity and complexity of mechanical parameters of roller compacted concrete dam(RCCD),the uniform design method,partial least-squares regression(PLS)and least squares support vector machine(LSSVM)were applied to the back analysis of RCCD with the use of the complex nonlinear relationship between dam mechanical parameters and dam displacements.During the process of back analysis,the initial samples of parameters were designed with uniform design method.Then,a transversely isotropic model of RCCD was established by MSC.Marc software.Through this model,training samples of LSSVM model could be obtained.And then,the complex nonlinear relationship between relative values of hydraulic components of dam displacements and mechanical parameters was established.Finally,actual relative values of dam hydraulic components are isolated from the measured data of dam displacements by using PLS.By inputting the isolated relative values into LSSVM model,the back analysis values of RCCD mechanical parameters can be obtained.The example analysis showed that mechanical parameters obtained by the above-mentioned back analysis method are reasonable,and the back analysis method is feasible.

HIGH-SPEED FLOW EROSION ON A NEW ROLLER COMPACTED CONCRETE DAM DURING CONSTRUCTION

A new roller compacted concrete dam of Fengman Hydropower Station is to be built in the toe of the old dam,which was identified as a dangerous dam.The new dam during construction would be influenced by the high-speed flow discharged from the old dam,which is an important problem to be considered for the first time in China,and which would affect the construction of the whole project.Therefore,a series of erosion experiments were conducted in this article.A high-speed flow erosion test apparatus was developed for the erosion experiments of the new dam materials.The maximum jet velocity goes up to 40 m/s and the section area of the nozzle is 0.0025 m2.In the process of experiments,the equipment shows a good performance.Erosive wear tests for two types of materials used in the new dam,a roller compacted concrete and a distorted concrete with four kinds of ages were carried out with the flow velocity in the range of 30 m/s-35 m/s.Erosion parameters and erosion laws for the two types of concretes with different ages were determined,and a general relationship between the erosion rate and the flow velocity is obtained as：,with the velocity exponent between 3.33 and 3.93.It is concluded that the erosion resistance of the distorted concrete is better than that of the roller compacted concrete and the mechanical properties of the concretes of over 14 d age are influenced slightly by the water impact.The test results might serve as a practical technique guide for the safety of this project during its construction in the flood season.

某水库大坝挡水坝段坝后渗漏探测及有限元分析

混凝土坝坝体渗漏影响大坝的安全性和耐久性,危及电器设备正常运行,应及时探查渗漏位置,消除渗漏隐患。为查明某混凝土挡水坝坝后渗漏原因,采用自然电位、跨孔声波、单孔声波、钻孔电视、钻孔取芯、注水试验、压水试验等多种方法对坝体混凝土质量进行检测,并基于检测成果开展有限元分析。检测发现:4号—5号坝段横缝存在渗漏异常,挡水坝段混凝土渗透系数不满足设计抗渗要求,各坝段混凝土存在不同程度蜂窝、离析、空洞和不密实现象,4号坝段520廊道与494廊道存在垂向渗漏通道,5号坝段钻孔之间混凝土存在渗漏通道,且廊道以下及向下游方向混凝土存在渗漏通道。有限元分析结果表明:515 m高程碾压混凝土与常态混凝土交界处为主要渗漏通道。

双峰寺水库大坝上游柔性防渗设计和施工要点分析

碾压混凝土大坝上游防渗设计和施工是这类坝型需要重视的关键环节,而碾压混凝土层面结合质量直接影响坝体的抗渗性,往往是碾压混凝土大坝防渗的薄弱环节。从碾压混凝土上游防渗设计、表面辅助防渗方案选择、原材料性能和施工要点等方面开展研究,最后选定双峰寺水库大坝上游防渗设计方案,明确施工要点,保证工程顺利实施。

Relationship between compressive and tensile strengths of roller-compacted concrete

The abstract roller-compacted concrete （RCC） is a zero slump concrete comprising the same materials as that of conventional concrete with different proportions. The RCC must be compacted to reach its final form. The effects of hydration and aggregate interlock on its strength are considerable. For similar binder contents, the compressive strength of the RCC is generally higher than that of the conventional concrete; however, the tensile strength of RCC may not be superior to that of the conventional concrete. Adequate tensile strength is necessary to resist fatigue cracking, particularly in pavement applications. However, the compressive strength is frequently used in assessing the quality control and quality assurance of pavements. Therefore, the relationship between the compressive and tensile strengths of the RCC should be analyzed. Unfortunately, only a few studies have been conducted on this relationship. The objective of this study is to identify the difference between the indirect tensile strengths of the RCC and those of the conventional concrete as well as develop relationship equations to evaluate the compressive and tensile strengths. In this study, regression equations are developed to estimate the indirect tensile strengths, which are known as flexural and splitting tensile strengths, using the compressive strength of the RCC. The results show that the flexural strength of the RCC is within the predicted values obtained from the conventional concrete equations for a given compressive strength. In contrast, the splitting tensile strength of the RCC is relatively lower than that of the conventional concrete for the given compressive strength.

翁结水库碾压混凝土重力坝动力特性及其抗滑稳定分析

重力坝是水利工程中最常用的主要水工建筑物之一,混凝土重力坝在地震作用下的动力稳定是坝工设计中的重要问题.本文以翁结碾压混凝土重力坝为对象,取位于河谷中的7、8号溢流坝段和9号非溢流坝段,建立三维有限元模型,通过计算分析了碾压混凝土重力坝在不同工况下的应力变形规律及抗滑稳定性.结果表明:静力荷载作用下,坝体位移符合重力坝一般规律,坝踵主拉应力范围较小;动力荷载作用下,位移等响应在坝顶达到最大,符合鞭鞘效应特征,同时坝体残余位移较小,坝体在一些部位出现瞬时拉应力超标现象,坝基塑性区未发生贯通;对7、8号坝段和9号坝段在建基面及碾压层面进行抗滑稳定验算,坝体坝基均满足稳定要求.

基于碾压混凝土破坏特征研究

以目前碾压混凝土重力坝坝体破坏特点为背景,利用扩张有限元数值方法,对碾压层厚度对大坝应力分布规律和裂缝扩展的影响进行了研究,并将在同一超载系数下的计算结果进行了比较,其中,超载系数从1.04~3.04,一共9种。在同样的过载条件下,裂缝的垂直延伸长度随碾压层的加厚而略有下降,裂缝的垂直延伸长度比正常情况下要小,仅在K=2.29、K=2.79两个位置与正常情况相当。大坝的压应力和物质的抗压强度相近,表明大坝在这个时候会出现总体失稳,而且裂缝的发展会转向沿河流的流向;在坝体各部位的材料达到对应的强度后,裂缝的横向发展速率会迅速增加,直至整个坝体的断裂。通过对4种不同荷载作用下坝体裂缝扩展深度、坝顶位移、坝踵及坝址处的受力情况进行了比较,结果显示,不同荷载作用下坝体裂缝呈现出脆性突发性破坏特征;结果表明:在荷载作用下,坝体裂缝扩展深度和坝顶位移均有一定程度的降低。

东南亚地区某碾压混凝土坝裂缝成因及防治措施研究

混凝土裂缝是影响水工结构强度和耐久性的主要因素之一,东南亚地区全年高温多雨,月均最大温差较小(8.6℃),年均温差大(20.2℃),混凝土温度容易控制,但裂缝问题时有发生。依托东南亚地区某碾压混凝土坝,采用有限元研究施工期温度应力的变化规律,分析混凝土开裂的敏感因素,并就其温控防裂措施开展详细研究。结果表明,浇筑长间歇及寒潮侵袭显著影响混凝土温度应力的变化,老混凝土的强约束作用及新老混凝土的温差影响叠加寒潮应力,导致混凝土应力超标出现温度裂缝。在上述研究的基础上,进一步探讨了降低新浇混凝土温度应力的温控措施,为东南亚地区大体积混凝土工程的建设提供一定的参考。

辉长岩骨料全级配碾压混凝土力学特性研究

辉长岩坚硬致密,具有高强度、高弹模特性,但将辉长岩骨料应用于大型水电工程在国内外尚无先例,缺乏可借鉴的工程实践经验,且湿筛碾压混凝土试件的力学性能无法真实反映全级配碾压混凝土的力学特性。对辉长岩骨料最大粒径为80 mm的全级配碾压混凝土的力学特性演化规律开展了系统研究,包括抗压强度、劈拉强度、轴压性能、轴拉性能、抗剪性能等,对比分析了全级配碾压混凝土抗压、劈拉强度及其湿筛试件的尺寸效应,并将试验结果与国内典型工程所用碾压混凝土的力学性能发展规律进行对比分析,此外还建立了辉长岩骨料全级配碾压混凝土抗压强度、劈拉强度、轴压性能、轴拉性能等力学性能-养护龄期演化函数模型。结果表明:辉长岩骨料全级配碾压混凝土的抗压强度、劈拉强度、抗剪等力学性能随龄期的发展规律符合国内同类工程碾压混凝土力学性能发展的一般规律;C_(90)20W8F100辉长岩全级配碾压混凝土试件与其湿筛试件抗压强度平均尺寸效应系数为0.80、劈拉强度平均尺寸效应系数为0.66;相关力学性能演化模型相关性高(R^(2)=0.9643~0.9992)。可见辉长岩骨料用于大型水电工程碾压混凝土坝建设具有可行性。

干热河谷气候环境对碾压混凝土性能的影响研究

采用大型步入式极端气候模拟器模拟干热河谷地区低湿度、强日照复杂气候环境,深入开展了大坝碾压混凝土力学性能、体积变形性能演化规律研究。结果表明,干热河谷气候环境对大坝三级配碾压混凝土的立方体抗压强度、轴压性能、轴拉性能等均存在较大影响,混凝土标准养护时间越短,干热河谷气候环境作用下混凝土的力学性能下降越明显;干热河谷气候环境下大坝三级配碾压混凝土的干缩变形呈双曲线模型演化规律,在干热河谷地区实施碾压混凝土工程应特别注意加强早期养护。

大华桥水电“满管群”入仓关键技术研究

大华桥大坝两岸边坡陡峭,马道宽度较窄,无法采用常规入仓手段。项目技术人员通过对实际地形的研究,采用满管群的形式进行入仓规划研究,在左右岸坝顶先浇筑一个坝段作为满管受料平台,通过满管+胶带机+满管的形式有效解决了左岸底部入仓、缺口入仓等技术难题,同时取得了右岸长近百米的满管应用、缺口高差45m的垂直满管应用技术成果。

西藏DG水电站大坝安全监测系统设计

基于相关规程规范和已建工程经验,结合西藏DG水电站坝址区水文地质条件、枢纽工程的布置及各建筑物结构形式,各项安全监测设施的特点,研究建立了大坝自动化安全监测系统。电站下闸蓄水至今,大坝安全监测系统运行正常,变形、位移、渗流等实测资料、现场巡查及相关复核计算成果表明,大坝工作性态正常,满足设计和相应规程规范等要求,自动化安全监测系统可供类似工程设计参考。

智能压实控制系统在穆棱市奋斗水库工程中的应用

奋斗水库项目是国务院确定的172个重点水利项目之一,是黑龙江省第一座碾压混凝土重力坝。传统的碾压混凝土施工主要靠机手的操作经验,容易出现漏压、过压的情况,传统的检测方法采用抽检方式,属于事后控制,存在费时、费工、抽检点密度小、检测结果不能真实反映整个施工作业面的压实度的实际情况。奋斗水库工程大坝碾压混凝土施工过程中采用了智能压实控制系统进行辅助质量管理,依靠智能化、信息化的连续监测技术,实时显示并记录整个碾压过程,有效控制大坝碾压混凝土施工质量。