多轴应力条件下碾压混凝土层面抗剪强度试验研究

针对碾压混凝土重力坝和拱坝等坝体真实的工作受力状况,对碾压混凝土拱坝所用的二级配混凝土材料成型的本体、层面处理和层面不处理试件,进行了单轴及多轴应力条件下的剪切试验研究。试件尺寸为150mm×150mm×150mm,试验比较了不同应力状态对本体和含层面试件的抗剪强度和变形特性的影响。结果表明：在低应力压剪和压压剪应力状态下,所有试件抗剪强度和极限变形均有所提高;在有拉应力存在的状态下,所有试件抗剪强度均有所降低;复合应力状态下三种试件强度和变形特性有一定的差异。在以上试验基础上提出了碾压混凝土在复杂应力状态下的多轴剪切强度破坏准则。     

碾压混凝土压剪强度分析

针对碾压混凝土受压剪作用问题,制作三级配本体、含层面试件和二级配本体、含层面试件,对试件进行单剪和双轴压剪试验,得到不同侧压应力下碾压混凝土的剪切强度。试验结果表明,施工层面削弱了碾压混凝土的抗剪性能;而侧压应力使碾压混凝土的抗剪能力显著提高,压应力越大,抗剪强度越高。根据双剪强度理论处理分析得到碾压混凝土的压剪强度曲线,该曲线与试验数据吻合,说明双剪强度理论真实反映了压剪破坏强度规律。     

动态压剪作用下碾压混凝土强度和变形研究

为了研究碾压混凝土材料在地震作用下的动态力学参数指标变化对大型碾压混凝土结构抗震动力反应和破坏过程的影响,使用改造后的液压伺服压剪试验系统对两种尺寸的碾压成型试块进行不同加载速率下的压剪试验,系统研究了二、三级配本体和层面试件在有法向压应力存在的状态下动态抗剪强度和变形性能。结果发现,碾压混凝土的峰值剪切强度随着剪切速率的增大而增大,增大幅度随着正应力的增大有减小趋势,残余剪切强度则随着剪切速率的增大略有减小,在试验基础上,建立了考虑不同试件类型和加载速率的破坏准则,为地震区的大型碾压混凝土结构层面受动态压剪组合荷载作用的动态分析提供了试验基础。     

基于神经元网络的碾压混凝土材料剪切本构模型研究

碾压混凝土的分层形式对其力学性能有较大的影响．为了全面探讨碾压混凝土材料力学性能及为碾压混凝土结构数值分析提供材料参数，研究和建立了基于损伤的碾压混凝土材料剪切本构模型．由于现场原位抗剪（断）试验条件的限制，试验无法量测出试件的真实应变值．在考虑碾压层面点的强度、应变局部化效应的基础上，基于岩滩水电站现场碾压抗剪（断）试验结果，采用损伤模型的本构形式进行了碾压混凝土剪切本构研究，并建立了基于神经元网络的碾压混凝土剪切本构模型．     

碾压混凝土拱坝诱导缝开裂试验研究

通过多组由深埋椭圆裂缝、深埋矩形裂缝和穿透裂缝3种型式形成不同削弱度的碾压混凝土试件轴拉试验，研究了试件的应力强度因子，分析了不同裂缝的应力强度因子计算公式。由于试件的断裂韧度与裂缝形式无关，假设深埋矩形预留缝试件的应力强度因子可以由深埋椭圆预留缝或穿透预留缝试件的应力强度因子通过修正求得，建立了矩形预留缝试件应力强度因子的近似解析表达式。考虑了尺寸效应后，求得碾压混凝土材料的断裂韧度。根据碾压混凝土拱坝诱导缝的构造特点，并考虑了相邻缝的影响计算出诱导缝开裂的等效强度。这一结果应用于沙牌碾压混凝土拱坝开裂计算的三维非线性应力场仿真计算中。     

两种级配混凝土试件双轴作用下强度、变形分析

水工大体积混凝土结构,如各种类型的重力坝和拱坝等,混凝土的大部分都处于明显的二轴或三轴应力状态,因此有必要进行水工上常用的大骨料混凝土双轴荷载作用下的强度和变形试验.对大坝三级配混凝土及湿筛二级配混凝土在双轴压、双轴拉-压荷载作用下的变形和强度特性进行了试验研究.观察了试件的破坏形态,根据试验结果分析了两种不同骨料级配混凝土试件峰值强度、极限变形的变化规律.分别在主应力空间和主应变空间建立了不同级配混凝土的破坏准则,为水工大体积混凝土按多轴强度理论进行设计提供了试验参考.     

多轴受力下混凝土强度和变形的试验研究

为模拟二滩高拱坝混凝土的复杂受力状况,利用研制的多功能真三轴加压装置,进行了混凝土试件的双轴、三轴受压,一轴受拉另一轴或另二轴受压下的强度和变形的试验研究。根据试验成果建立了双轴、三轴各应力问关系的回归方程及应力与应变关系式。本项研究为校核二滩高拱坝混凝土的安全度、为高拱坝设计中考虑混凝土的力学特性提供了数据。     

江口水电站岩石力学试验研究

江口电站的大坝为混凝土双曲拱坝，最大坝高139m，坝址岩体中存在大量的软弱夹层，拱座的变表及稳定受夹层的变形特性及抗剪强度控制，为此进行了岩体及夹层变形特性试验，混凝土与基岩，结构面以及岩一身的抗剪强度试验，岩体皮测试，地应力测试以及室内岩石力学试验研究，并据此提出了岩石单轴抗压强度，变形模量，抗剪强度等参数的建议值。     

二潍拱坝混凝土设计及试验研究

二滩水电站混凝土双曲拱坝，坝高２４０ｍ，是我国已建和的第一高坝。根据拱坝应力状况，仿真试验试件尺寸，二向三向轴受力状况混凝土力学变形特性，建立了相应的方程式。二滩拱坝混凝土强度设计龄验试件尺寸，二向、三向轴受力状况混凝土的力学特性，建立了相应的方程式。二滩拱坝混凝土强度的设计龄期为１８０ｄ，抗渗标号不小于Ｓ１２，抗冻标号选用Ｄ２００，胶村用量不超过２００ｋｇ／ｍ＾３也少于１７０ｋｇ／ｍ＾３，粉煤灰     

真实水荷载对混凝土强度影响的试验研究

为了了解混凝土材料在水环境中的力学性能，本文试验研究了混凝土在水中及三轴应力状态下的抗压强度特性。试验在大型多功能静动三轴仪上进行，混凝土试件采用Φ100mm×200mm圆柱体试件，试验中考虑了不同的水荷载作用方式、围压和湿度含量的影响。试验的水荷载作用方式分为机械围压(试件密封)和真实水围压(试件不密封)两种。围压大小分别为0、2和4MPa。为了确定湿度对混凝土强度的影响，进行了干燥和饱和两种湿度混凝土的三轴压缩试验，并进行对比。试验研究表明，试件密封条件下，干燥和饱和混凝土的强度均随围压增加且效应明显，但干燥混凝土比饱和混凝土的围压效应更显著；在试件不密封条件下，混凝土三轴强度比密封条件下的强度低。试件不密封条件下，饱和混凝土的三轴强度接近其单轴强度，但干燥混凝土强度降低较大。文中还基于混凝土内部孔隙水压力和外部水荷载的相互作用机理，对试验结果进行了初步解释。     

Call for Papers

正As the eldest and most distributed professional journal of water industry,Water Wastewater Engineering(W WE)gained very wide acceptance from the colleagues working in this field in this country since start publication in 1964.Now it is administrated by the Ministry of Construction of the People’s Republic of China and sponsored by the China Civil Engineering Society etc.     

库水波动下库岸边坡地下水浸润线解析解及误差分析

解析法是库岸边坡地下水浸润线计算中便于实际应用的方法,但该方法须基于若干假定并对潜水运动基本方程线性化后才能求解。针对各假定和线性化过程建立不同的地下水渗流数学模型,用解析法和有限元法解答上述数学模型,分析各误差大小及其规律。结果表明：库岸垂直处理带来的误差要小于方程线性化处理和不考虑非饱和渗流带来的误差,而且它们都随渗透系数变大而减小;在三峡库区库水调度情况下,假定库水位等速变化带来的误差对大多岸坡而言可以忽略;计算库岸边坡地下水浸润线时,解析法只适用于水位变化幅度相比含水层厚度较小,且几何边界规则、岩土结构简单、岩土体渗透性较好时的情况。     

Changes in Summer Irrigated Crop Area and Water Use in Southeastern Turkey from 1993 to 2002: Implications for Current and Future Water Resources

Changes in summer irrigated cropland acreage and related water use are estimated from satellite remote sensing and ancillary data in semi-arid Southeastern Turkey where traditionally dry agricultural lands are being rapidly transformed into irrigated fields with the help of water from the Euphrates-Tigris Rivers. An image classification methodology based on thresholding of Landsat NDVI images from the peak summer period reveals that the total area of summer irrigated crops has increased three-fold (from 35,000 ha to over 100,000) in the Harran Plain between 1993 and 2002. Coupled analysis of annual irrigated crop area from remote sensing and potential evapotranspiration based estimates of irrigation water requirements for cotton indicate a corresponding increase in agricultural water use from about 370 million cubic meters to over one billion cubic meters, a volume in accordance with the state estimates. These estimates have important implications for understanding the rapid changes in current agricultural withdrawals in Southeastern Turkey and form a quantitative basis for exploring the changes in future water demands in the region. For example, expansion of irrigated lands have led to a steady decrease in potential evaporation due to increased roughness and decreased humidity deficit in the Harran Plain. Assuming that the changes in future evaporation conditions will be of similar nature, water use for irrigation is expected to decrease over 40 percent in future irrigation sites. Incorporating this decrease in overall planning of the irrigation projects currently under construction should lead to improved management, and by extension, sustainability of water resources in the region.     

浅谈优化Vray渲染在制作三维场景的应用研究

用Vray三维渲染引擎来渲染三维场景,其质量和速度是由一些影响因素和参数设置决定的,不同的参数和因素,可以得出不同的三维渲染效果.因此,分析、优化三维渲染质量和速度的影响因素,正确、合理的选择参数对提高Vray最后渲染阶段的质量和速度非常重要.     

固结、渗流和沉积控制方程研究

本文从两相流体动力学的守恒方程出发，考虑固相、液相的相对运动，推导了可以考虑场的不均匀性和流体压缩性的统一形式的控制方程，并对方程所基于的物理概念和相互联系进行了必要的分析。通过对方程适当形式的表达，可导出用于大、小变形固结、渗流和沉积的简化方程，显示了在不同领域的三个理论存在一定的统一性。方程推导过程并未对本构关系加以限制，适用范围较广。依据实际问题的要求，作了不同形式的简化。     

四川省及重庆市中型水电站效益分析

该文分析了四川省及重庆市几座中型水电站的调查材料表明：四川省及重庆市中型水电站不仅在川渝主网和地方电网中起着很大的作用，并具有巨大的社会效益，同时还有综合利用效益，说明修建中型水电站的优越性．     

Site modelling methods for detecting hydrologic alteration of flood frequency and flood duration in the floodplain below the carlyle dam,lower Kaskaskia River,Illinois, USA

Reports concerning the influence of dams on river hydrology vary among researchers, interest groups and government agencies. These often contradicting statements may occur because changes in hydrology caused by dams are distinct for each dam and river watershed. The objective of this research was to use site specific techniques to determine if the 1967 installation of the Carlyle Dam, lower Kaskaskia River, Illinois, altered flood frequency and duration within the forested floodplain located below the dam. Results indicated a decrease in flood duration and frequency, and a decrease in annual flood frequency variation at a site 6.4 km below the dam. Pre‐dam versus post‐dam differences in flood frequency and duration at the site 32.2 km below the dam were related to climate rather than dam effects. Although dam impacts are a concern, this research shows that distance downstream from the dam and downstream tributary and watershed characteristics should be considered before assuming that the dam has changed hydrologic parameters for portions of rivers. This research also indicates that areas of the lower Kaskaskia River may still maintain hydrologic ecological integrity, and could be targeted for restoration and adaptive management purposes. Hydrologic modelling combined with river gage and on‐site well measurement techniques presented in this study could provide detailed flood frequency and duration information for land use, sociological and geomorphological questions in focus areas within river floodplains. Copyright © 2008 John Wiley & Sons, Ltd.     

Statistical tools for thermal regime characterization at segment river scale: Case study of the Ste‐Marguerite River

Suitable thermal fish habitats are constrained by both maximum and minimum temperature tolerances. A multivariate and geostatistical approach was developed to estimate stream thermal characteristics at the river segment scale. Data from 22 temperature‐monitoring stations during summer 2007 were used to estimate monthly maximum temperature as well as thermal characteristics such as the number of events, the cumulative degree–days and the associated duration over specific temperature thresholds of 19 and 21°C. The probability of exceeding these temperature thresholds has also been interpolated. The methodology relies on the construction of a multivariate space using physiographic and hydrological characteristics of gauging stations as inputs in a canonical correlation analysis (CCA). A geostatistical interpolation technique, ordinary kriging, was subsequently used to perform interpolation in the physiographical space constructed using CCA. Results from this study were obtained for thermal characteristics estimated into two different interpolation spaces: (1) a 7 metrics space, and (2) an 8 metrics space. Cross‐validation technique has been performed and satisfactory results were obtained. Kriging thermal characteristics (magnitude and duration) into the 7 metric space for a 19°C threshold exceedance leads to best results with Relative Root Mean Square Error (RRMSE) ranging between 9.66 and 15.08%. The study shows that kriging in a multivariate space is a promising tool for water resources managers, especially in cases where risk mapping for lethal or sub‐lethal temperature thresholds may be required for a specific fish species. Copyright © 2010 John Wiley & Sons, Ltd.     

掺MgO混凝土的宏细观试验研究

利用MgO膨胀剂的延迟微膨胀效应能显著提高大体积混凝土的力学性能,产生的预压应力还能有效提高大体积混凝土抵抗温度开裂的能力,但目前对其微观机理研究不多。采用宏观与微观相结合的方式,研究了不同活性指数、不同掺量的MgO混凝土的力学性能,利用SEM/EDS微观分析手段揭示了MgO对混凝土性能影响的作用机理。试验结果表明：MgO取代部分水泥掺入混凝土中,混凝土的力学性能降低;掺量为4%~5%时,活性指数为100s的MgO混凝土的膨胀率大于活性指数为50 s的MgO混凝土;MgO混凝土的膨胀特性与Ca,Si,Mg,Al等元素的分布情况有关,掺入的MgO将改变界面区Ca,Si,Mg元素的富集特性,Ca元素和Mg元素更易于在界面区富集,导致混凝土宏观力学性能的降低。     

基于MIDAS软件探讨施工工序对深基坑稳定性的影响

基于武汉地铁名都站深基坑工程与水文地质勘察资料,建立了三维工程地质仿真计算模型。依据名都站深基坑开挖支护方案,利用有限元软件MIDAS的摩尔-库仑本构模型,对武汉地铁名都站深基坑施工过程中,不同施工工序下每步开挖之后,基坑的变形情况做仿真模拟计算,并对比分析其对基坑稳定性的影响。结果表明：基坑围护结构的变形情况与施工工序有很大的关系,施工工序越合理,上部土体变形越小,反之越大。因此,在基坑工程的施工过程中,要注重施工步骤的划分与合理安排,从而保证基坑工程的安全。研究成果为以后武汉地区基坑工程的施工设计提供了值得借鉴的经验。