水电站大坝碾压混凝土温控措施应用研究

象鼻岭水电站位于贵州省威宁县与云南省会泽县交界处的牛栏江上,水库坝高141.5m,碾压混凝土工程量为81.93万m3,地处暖温带高原季风气候,受季风、地形、低纬的影响形成复杂多变的气候特征。象鼻岭水电站大坝是目前世界上第二高碾压混凝土双曲拱坝,大坝具有工程具有规模大、技术含量高、施工要求高等特点。大坝碾压混凝土温控问题十分突出,成为质量和进度的控制关键。针对象鼻岭水电站水文气象条件、工程施工特点及大坝碾压混凝土温度控制标准,为防止建筑物有害裂缝发生,对碾压混凝土浇筑的温度控制施工技术进行了系统的研究,突破了传统的碾压混凝土温控理念,大胆采用优化混凝土配合比、降低入仓温度、通水冷却、视频监控等新工艺、新技术进行碾压混凝土温度控制,取得良好的温控效果,使碾压混凝土的施工质量得到了更可靠的保证,为类似工程项目提供借鉴和指导。     

大体积混凝土放热过程试验监测与仿真

大体积混凝土因导热系数、浇筑温度等影响因素,在浇筑混凝土后因温差过大易产生温度裂缝。通过在混凝土配合比设计中掺入一定量的粉煤灰,减小混凝土绝热温升。以工程实例为基础建立三维模型,并将实测数据与COMSOL模拟结果进行对比分析,再用COMSOL软件从不同的影响因素对其进行模拟分析。模拟结果表明:掺加粉煤灰的混凝土在浇筑大体积混凝土时,若外界温度较低,仍将产生温度裂缝。低温环境下,改变混凝土浇筑温度对混凝土裂缝控制影响不大,可通过适当调节混凝土的导热系数,使混凝土温度梯度符合施工规范要求。     

分布式光纤传感用于大坝基座裂缝监测

分布式光纤传感技术对大型混凝固结构,如大坝与桥梁,进行裂缝监测意义重大,其分布式检测能力对具有强随机性的大坝裂缝监测效果更显著.一种新型分布式光纤传感器埋入混凝土并与预期裂缝相交一定斜角,当裂缝出现引起光纤局部微弯,并诱发瑞利散射光产生衰减,用光时域反射技术实现分布式检测.将该种传感器用于四川石棉冶勒大坝裂缝监测,结果表明:该光纤传感器不仅对裂缝宽度、位移具有高分辨率(0.02 mm)、大动态范围(4.8 mm),而且有较高的定位分辨率(0.2 m),为发展该类分布式光纤传感监测系统提供了较好的技术基础.     

基于改进Yolov5s的混凝土坝裂缝检测研究

大坝作为我国的重要水利工程，其安全性不言而喻。裂缝作为大坝的主要安全隐患，大坝裂缝的智能化检测，对管控大坝风险具有非凡的意义。提出一种基于改进YOLOv5s目标检测算法的大坝裂缝检测方法。首先，在YOLOv5s的主干特征提取网络中引入轻量级GhostNet中的Ghost模块，对YOLOv5s的主干网络进行优化，得到轻量级的模型YOLOv5s-Ghost,以降低模型的复杂度，提高裂缝的检测速度；然后在模型预测输出端融合高效的CA(Coordinate Attention)注意力机制进一步增强裂缝特征提取能力，提高裂缝模型检测的性能。实验结果表明：该方法与现有的YOLOv5s相比，模型大小复杂度降低了44.8%,准确率提升了2.6%,验证了改进方案的有效性，提高了裂缝检测效率。通过引入GhostNet中的Ghost模块和融合CA注意力机制相结合，使得YOLOv5模型的复杂度降低，参数量减少，实现了对裂缝检测速度与精度的提高，增强了网络性能。     

高精度混凝土裂缝宽度智能监测系统设计

为了能自动定时监测裂缝宽度及其变化,避免传统人工裂缝宽度监测方法耗时、耗力且人工读数误差大等缺点,设计了一种基于STC90C54AD与ELIS-1024的混凝土裂缝智能监测系统;采用单片机STC90C54AD作为处理器,利用CMOS图像传感器ELIS-1024对裂缝表面进行成像,通过对图像进行去噪、平滑、边缘识别后提取裂缝信息,进而计算裂缝的宽度;给出了整个系统的设计思路及相应的硬件电路图、图像处理算法等;通过实验验证,该系统稳定可靠、使用方便,精度高达0.004mm;适合用在桥梁、大坝、房屋、道路等混凝土裂缝宽度监测领域。     

建筑工程施工中混凝土浇筑施工

本文介绍了混凝土浇筑施工的工艺流程,施工单位需要合理选择混凝土制作材料;按照流程进行混凝土的制作;注重混凝土浇筑现场的管理;根据建筑工程不同区域的需求,选择相应的混凝土浇筑施工工艺;还需要加强对混凝土浇筑施工的管理,以此提升混凝土浇筑施工水平,强化建筑工程品质。     

基于Multi-Agent的混凝土坝浇筑仿真模型框架

混凝土坝浇筑计算机仿真是施工管理的重要依据之一。然而由于以往所建立的仿真模型多是基于工艺因素，缺乏对管理因素的考虑（像承包商的经济目标等），使得仿真系统很难准确地模拟真实的环境。基于多Agent系统的混凝土坝浇筑计算机仿真模型可以考虑工艺和组织管理两个方面的因素，使建立的模型更具实用性并提高描述问题的深度和广度。该文在对现有模型应用中存在问题分析基础上，提出了一种混凝土浇筑多Agent系统建模的构架，它把混凝土浇筑过程看作协商过程，使得施工管理人员可以得到更多的信息并进行交互。这一框架使得混凝土浇筑施工仿真模型更加具有智能性和价值性。     

建筑工程施工中的混凝土浇筑施工技术研究

作为建筑行业的重要材料,钢筋混凝土在工程中有着无可替代的地位,随着工程施工规模的扩大,混凝土浇筑施工技术不断发展,不同结构采取的施工技术有所差别。基于常见的几种混凝土浇筑技术,分别从混凝土搅拌、混凝土浇筑、混凝土捣实以及混凝土养护几方面阐述混凝土浇筑施工技术在不同建筑结构中的实践应用。在建筑工程施工项目中,混凝土浇筑技术至关重要,不仅要保证混凝土的材料质量,还要确保技术合格,施工工序正确。混凝土施工环节众多,在浇筑过程中,受到的影响因素比较多,不断革新与发展混凝土浇筑技术,保证混凝土浇筑的施工质量,对于提高建筑工程的整体施工质量是至关重要的。针对这种情况,本文对建筑工程施工中混凝土浇筑施工技术进行研究,以供相关人员参考。     

谈对桥梁施工技术的分析

为防止大体积混凝土裂缝的产生，应从降低温度应力和提高混凝土的极限拉伸强度两方面着手。做好冷却和保温，浇筑前避免材料过热，浇筑后保温，降低温度应力。提高混凝土的极限拉伸，缓慢降温可充分发挥混凝土的应力松弛效应，提高抗拉性能。严格控制砂石质量，限制含泥量，正确选用混凝土级配，适当掺用外加剂，减少用水量，改进混凝土浇筑工艺。是提高混凝土强度的有效方法。     

混凝土生产浇筑过程的建模及资源配置分析

在详细描述混凝土生产浇筑系统工作过程和资源配置的基础上,建立了混凝土生产浇筑系统的排队论模型,针对所建立的排队论模型GI/M/4,对混凝土生产浇筑系统资源配置的合理性进行了理论分析,结果表明,实际系统的资源配置基本合理,同时验证了文中建立的排队论模型的正确性.     

Determination of the type and thickness for impervious layer in RCC dam

The distribution of temperature is simulated using 3D finite element relocating mesh method (TDFERMM) for the third grader roller compacted concrete (TGRCC) dam with different material and different thickness of impervious layer, including conventional concrete (CC), grader-enrich-concrete (GEVRCC) and second grader roller compacted concrete (SGRCC) during construction period. The calculated results show that the different types of impervious layer have no impact on the temperature distribution of dam. However, the thickness of impervious layer has greatly influenced the temperature distribution of dam, and a conclusion can be drawn that the middle thickness from 3 to 5 m of SGRCC impervious layer can meet the demand of temperature control for third grader roller compacted concrete (TGRCC) dam.     

The development and verification of relocating mesh method for the computation of temperature field of RCC dam

Based on the construction property of rolled compacted concrete dam cast layer by layer, three-dimensional finite element relocating mesh method was developed in the paper to simulate construction process and compute temperature field. The computation model of relocating mesh method is expatiated in detail. The feasibility and error of the relocating mesh method were analyzed and demonstrated. The computation results were verified with the temperature observation data of an RCC arch dam. The results show that the method has high calculation precision, less computer run time and less memory. The values computed with the method are in the same trend with the observation data. The method has proved to be effective in simulating construction process and computing temperature field of RCC dam.     

Concrete breakout strength of single anchors in tension using neural networks

A feed forward neural network model for evaluating the concrete breakout strength of single cast-in and post-installed mechanical anchors in tension is presented. The nodes of the neural network input layer represent the embedment depth, anchor head diameter, concrete strength and anchor installation system, and the neural network output is the tensile capacity of anchors as governed by the concrete breakout. Three different techniques have been adopted to represent the anchor installation system in the neural network input layer. The training, validation and testing of the developed networks were based on a database of 451 experimental tests obtained from previous laboratory anchor tests. Testing of the trained neural network indicates good predictions of the concrete breakout strength of cast-in and post-installed mechanical anchors in tension.The relationships between the concrete breakout strength of anchors and different influencing parameters obtained from the trained neural networks were in general agreement with those of the ACI 318-02 for cast-in and post-installed mechanical anchors. It has been shown that the concrete breakout strength of anchors in tension is approximately proportional to the embedment depth of 1.5 power and marginally affected by changing the anchor head diameter.     

Simulation analysis of thermal stress of RCC dams using 3-D finite element relocating mesh method

The 3-D finite element relocating mesh method is developed for simulation analysis of temperature and thermal stress distribution in a roller compacted concrete dam during the construction period. According to the relation between specific properties and age of concrete, some meshes are merged into a larger mesh or a few larger meshes when the age of the concrete is appropriate. Using this method, the total number of elements and nodes were remarkably reduced when the dam height was increased. When the change in elastic modulus, creeps and hydration heat is within the limits permitted by design criteria, the relocating of mesh will start. Using this method, a 3 D simulation analysis of thermal stress in a roller compacted concrete (RCC) high dam can be realized by microcomputer and appeared at the construction site. On the basis of real factors during the construction period, an engineer can predict the distribution of temperature and thermal stress in the RCC dam. Therefore, engineers can take appropriate measures to control the concrete temperature to reduce the thermal stress and avoid crack development within the dam.     

Development of finite element computer code for thermal analysis of roller compacted concrete dams

Thermal analysis of roller compacted concrete (RCC) dams plays an important role in their design and construction. This paper deals with the development of a finite element based computer code for the determination of temperatures within the dam body. The finite element code is then applied to the real full-scale problem to determine the impact of the placement schedule on the thermal response of roller compacted concrete dam. Based on the results obtained, it could be concluded that for a given roller compacted concrete dam, changing the placing schedule can optimize the locations of maximum temperature zones.     

Ultimate bearing capacity of concrete dam involved in geometric and material nonlinearity

To get the actual ultimate bearing capacity of concrete dam, the effect of geometric nonlinearity and strain softening on it, which appears in the failure process of concrete dam, is studied. Overload method is adopted to obtain the bearing capacity of a concrete dam by taking into consideration strain softening in the material constitutive law, geometric nonlinearity in geometric equation and equilibrium differential equation. Arc-length method is used to find the extreme point and descending branch of the...     

Study on early warning index of spatial deformation for high concrete dam

Owing to the deficiency in early warning for high concrete dam,a formula was established to characterize the deformation behavior of high concrete dam as a whole.The early warning index of spatial deformation was calculated by low probability principle on the basis of the deformation entropy formula proposed.The steps were as follows.Firstly,the probability method was utilized to define the degree of order and degree of chaos for each survey point.Secondly,the weight distribution among the survey points was...     

大石门水电站大坝安全监测设计与资料分析

大坝安全监测关系到大坝的施工质量和运行安全,是工程施工和运行期的重要工作。针对沥青砼心墙堆石坝的特点,通过优化监测设计方案,设置关键监测项目,选择对沥青砼心墙结构影响小的监测仪器和安装方式,实现大坝关键部位的安全监测。对近 10 a 的监测数据进行处理和分析,结果表明监测仪器工作正常,监测数据连续可靠,大石门水电站大坝和沥青砼心墙运行稳定,说明大坝安全监测设计方案合理、正确,为全面掌握和了解大坝的施工质量、运行状况等发挥重要作用。     

柏叶口水库面板堆石坝变形数值分析

为了解柏叶口面板堆石坝变形规律,通过单元尺寸和曲率因子优化及多步逐级加载模拟大坝施工加载过程,应用COMSOL Multiphysics软件获取大坝竣工期、正常蓄水位、设计及校核洪水位4种工况下的,河床处180、左岸60及右岸245等断面的典型剖面的变形,结合某混凝土面板堆石坝工程,考虑分级加载的情况下,仿真模拟大坝填筑、混凝土面板浇筑过程,分析混凝土面板堆石坝的变形特性。研究结果表明本工程施工速度快对大坝整体变形规律改变不大,可为下一步预警指标的拟定提供参考。