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

According to the characteristics of thin-layer rolling and pouting 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.

Design of Hard Compaction Rollers for Automated Fiber Placement on Complex Mandrel Geometries

This paper presents a methodology for designing hard compaction rollers for an AFP(automated fiber placement)head with a hot gas torch heating system for laying thermoplastic CFRP(carbon fiber reinforced plastic)tapes.Some manufacturing defects and alternative designs are reviewed to highlight the importance of AFP compaction roller conformity and surface adhesion.The formulation of a general parametric description of the design challenge is derived and adequately addresses the problem on a tow-to-tow basis.

The influence of roller compaction processing variables on the rheological properties of granules

This study is part of an ongoing project to enable the full specification of the Design Space for roller compactor systems and shows how the processing parameters influence the behaviour of the product granulate from a placebo formulation. Granulate was produced using a proprietary roller compactor by varying the compaction pressure and gap width,and the dynamic, bulk and shear properties of the resultant granulates were measured.The results demonstrate several rheological properties of the granulate, which have been shown to be closely correlated with variance in die filling and tablet strength, and are predictably influenced by the processing parameters.

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 realime estimation method of compaction quality for the entire work area of roller compacted concrete dam was proposed finally. The adaptive adjustment of the roiling 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.

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.

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.

振动压路机的能量传递模型与作业参数优化研究

为提高振动压路机作业过程的压实质量,研究了振动压路机的能量传递模型与作业参数优化。首先基于U-K方程建立“碾轮-被压实材料”的系统振动动力学模型,结合能量守恒提出振动压路机能量传递模型;然后以振动频率和压实速度作为寻优工作参数,构建路面压实质量的优化模型;最后通过案例验证证明了所提方法的可行性与有效性。结果表明:工作频率与被压实材料的固有频率比值保持在√2~2范围内,可避免共振带来的影响;初始阶段低速碾压,材料性能稳定后提高碾压速度可保证高效压实,得出振动频率在21.8~27 Hz、压实速度在2.36~2.91 km/s范围内,可达到最优的压实效果。所提的能量传递模型、作业参数优化模型为保障振动压路机压实质量奠定了基础,为提高振动压路机压实质量和效率提供了参考。

碾压混凝土分层碾压离散元模拟及施工成层细观机理研究

碾压混凝土(RCC)坝特有的大仓面分层碾压工艺带来的层间结合质量问题,是影响其安全运行的重要因素。从施工控制的角度分析RCC施工成层机理,进而合理调整碾压参数,可有效保证大坝的施工质量。首先,通过RCC分层碾压试验,分析了碾压过程中含层面RCC的沉降规律、压实度及抗剪强度,为后续离散元模拟提供了基础;然后,建立并验证了RCC双层碾压与抗剪试验离散元模型;最后,给出了表征层间结合质量的骨料嵌入值指标,进而从孔隙率、层间骨料嵌入、层面应力分布、层间抗剪强度等方面分析了RCC施工成层的细观机理。结果表明:碾压参数对RCC的嵌入值、压实特性、层面应力和层间结合质量均有一定影响;嵌入值是影响层间抗剪强度的重要因素,二者呈线性相关,嵌入值每增加1 mm,模拟抗剪强度约增加1.583 MPa;激振力的增加以及行进速度、碾压厚度的减小均有利于提高层间结合质量,且碾压厚度是影响层间结合质量的最敏感参数。研究结果可为施工中RCC层间结合质量控制标准的制定提供理论依据。

层面处理对碾压混凝土剪切过程中裂缝扩展的影响

为研究碾压混凝土层面剪切过程中的裂缝扩展规律,本文针对不同层面处理的碾压混凝土开展抗剪强度试验,分析了不同试件的破坏形态和抗剪强度变化规律,同时运用数字图像相关技术观测碾压混凝土剪切过程中层面裂缝发展规律,并结合热重技术分析了层面水化程度对裂缝扩展的影响。结果表明:层面处理可以有效提高层面结合效果和抗剪强度,降低裂缝宽度和扩展速率,经过纳米SiO_(2)砂浆处理的碾压混凝土层面结合效果最佳,裂缝最大宽度和扩展速率分别降低至0.528 mm和1.412 mm/s;层面裂缝发展过程分为初始、萌生、扩展、贯通四个阶段;纳米SiO_(2)能够促进水泥水化,水化产物含量与最大裂缝扩展速率呈负相关关系,因此纳米SiO_(2)的加入可有效降低层面裂缝扩展速率。

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。

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。

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。

基于动应力响应的路基振动碾压性能仿真分析

为探究路基振动压实的动力响应特性,开展路基振动碾压的仿真分析,研究碾压过程中路基的竖向动应力响应分布规律,分析动应力沿路基深度及宽度方向的衰减效应,并探索压路机振动频率、名义振幅和碾压速度对路基内动应力分布的影响。结果表明:振动碾压下,路基内的竖向动应力近似呈长轴沿竖向的椭球状分布,振动能量主要沿深度方向传递,路基动应力随深度增加呈典型的指数函数规律衰减;振动频率28 Hz时产生共振现象,路基中竖向动应力达到最大值,说明此时土体吸收了更多的振动压实功,进而可达到更好的压实效果;随深度增加,路基中竖向动应力随名义振幅增加的增长速率逐渐减小,而其随碾压速度增大的衰减速率则有所增大。

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.

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。

基于毫米波雷达和相机融合的无人碾压机施工障碍物快速精准感知方法

对施工环境的快速精准感知是保证无人碾压机安全、稳定运行的基础。然而当前坝面碾压施工过程中无人碾压机仅依靠毫米波雷达对障碍物的距离进行感知,当距离小于给定阈值时,碾压机由于无法感知障碍物的类别,常引起障碍物的误识别,导致无法进行后续碾压作业。针对上述问题,本研究提出基于毫米波雷达和相机融合的无人驾驶碾压机施工障碍物快速精准感知方法。首先,该方法将快速区域卷积神经网络(Faster R-CNN)特征提取网络中的卷积运算核替换为不同扩张率的空洞卷积核(DC),实现对坝面障碍物类型的快速精准识别。然后,将毫米波雷达感知到的障碍物距离、速度信息与相机感知到的类别信息进行融合,实现对坝面环境的全面精准感知。工程案例表明,相较于现行的Faster R-CNN目标检测算法,本研究提出的DC-Faster R-CNN目标检测算法mAP(检测各类障碍物的平均精度值)提高了2.59%,每张图片的检测时间减少了0.015 s;同时,基于多元信息融合的感知策略实现了碾压施工过程中的精准避障,保证了坝面施工的安全和效率。

基于融合GNSS/UWB/RTS的RCC坝智能监控定位补偿方法研究

近年来,大坝压实质量的智能监控技术逐渐成为研究热点。现有的碾压混凝土(RCC)坝碾压作业过程实时监控技术依赖于全球导航卫星系统(GNSS),然而,对于建设在深窄河谷地区的RCC坝,GNSS系统易受两侧山体信号遮挡干扰。针对上述问题,本研究提出一种基于融合GNSS/UWB/RTS的RCC坝碾压施工智能定位补偿技术。首先,依据悬崖边壁、倒悬体遮挡处的环境特征建立了适用于深窄河谷地区的RCC坝碾压实时监控数学模型;其次,引入了超宽带(UWB)和机器人全站仪(RTS)定位补偿技术,采用耦合新息阈值与最小二乘的改进卡尔曼滤波算法融合GNSS/UWB/RTS的定位数据,实现了遮挡环境下卫星信号的连续稳定定位监控;最后,在西南某大型RCC坝工程中得到应用。结果表明,该方法能够实现对深窄河谷中RCC坝碾压施工的全地形、全过程实时监控,可弥补单纯依赖GNSS进行碾压过程实时监控所不足。