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二级配混凝土材料成型的本体、分层处理和分层不处理试件，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都有所提高，在有拉应力存在的状态下，所有试件抗剪强度有所降低，复合应力状态下三种试件强度和变形特性有一定的差异。在以上试验基础上给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。     

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。     

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。     

不同骨料级配混凝土的双轴压强度试验和破坏准则

针对某大坝实际工程,用液压伺服静动态三轴试验系统,对某大坝工程不同骨料级配和尺寸的混凝土试件在双向压荷载作用下的变形和强度特性进行了试验研究。试件采用大坝原级配最大骨料粒径为80mm的立方体试件以及相应的湿筛混凝土试件,尺寸分别为250mm×250mm×250mm、150mm×150mm×150mm、100mm×100mm×100mm。试验过程测得了所有试件两个加载方向的应力和应变以及未加载方向上的变形,探讨了不同级配混凝土的双轴抗压强度、极限变形、应力-应变曲线以及破坏形态的变化规律。试验发现大骨料混凝土在双轴压作用下的极限强度和变形能力要比相应的湿筛小骨料混凝土提高的更多,最后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。     

碾压混凝土层面抗剪(断)特性尺寸效应研究

碾压混凝土呈层状结构,大约30cm厚为一层,大量的层面成为薄弱环节,层面抗剪强度参数为碾压混凝土重力坝抗滑稳定分析的重要依据。碾压混凝土层面原位抗剪试验是提供层面抗剪参数的主要试验方法。这种试验的试件大、投资多、工作量大,又是大型工程中必不可少的试验项目。结合龙滩碾压混凝土特性试验,研究试件大小对抗剪参数的影响,确定了原位抗剪试验试件的尺寸效应系数,并提出了一个表达式,从而可用小试件代替大试件研究抗剪参数。这将有较高的理论价值和实用价值。     

胶凝砂砾石层面抗剪参数试验研究

胶凝砂砾石坝由于骨料多,水泥掺量少,本体抗剪强度很低,而且胶凝砂砾石坝采用碾压施工,水平向碾压层面的存在,会导致层间结合力的降低,影响层面的抗滑稳定及抗渗安全,因此研究胶凝砂砾石碾压层面抗剪能力具有重要意义。本文根据胶凝砂砾石碾压层面的处理措施,设计了6种试验方案进行胶凝砂砾石碾压层面的抗剪断试验,采用150mm立方体试件研究了单轴压条件下的胶凝砂砾石碾压层面抗剪断特性。并在守口堡大坝坝基不同高度的碾压层面处,采用50cm立方体试件进行了富浆胶凝砂砾石原位抗剪断试验。通过室内和原位试验研究,得到了胶凝砂砾石层面抗剪断基本参数,并通过分析揭示了胶凝砂砾石层面剪裂机理,对比了室内试验与原位试验结果的差异并揭示了其原因,对比了富浆胶凝砂砾石层面原位抗剪参数与RCC的差异。上述研究,为胶凝砂砾石大坝的结构分析提供了可靠的参数,并为碾压层面的施工提供了有益的建议。     

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．     

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.     

水口电站明渠导墙碾压混凝土抗剪强度特性试验研究

碾压混凝土坝体中存在着众多的水平层面，而层面的各种物理力学性质比碾压混凝土本身差，在结构应力、温度应力作用下，对坝体的抗滑稳定、整体性及防渗性均可能产生不利影响。对水口电站明渠导墙不同层面碾压混凝土进行的变形性能和抗剪强度试验研究，取得了较丰富的现场资料，得到了一些感性认识。     

试件尺寸对碾压混凝土层面抗剪断强度的影响

通过碾压混凝土层面原位抗剪断试验和三维非线性有限元分析，研究试件尺寸对抗剪断强度的影响，得出了碾压混凝土层面抗剪断强度的尺寸效应表达式，试验结果表明，碾压混凝土层面抗剪原位抗剪断强度指标的尺寸效应明显，f′和c′的值均随试件尺寸的增大而减小，且c′值随尺寸变化的程度更大。三维非线性有限元分析得到的f′和c′值与试验拟合的参数基本吻合，计算值略小于试验值。     

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.     

地下厂房施工过程的三维非线性数值模拟分析

根据冗各电站地下厂房开挖支护的施工顺序,以隐式杆单元模拟锚杆,以壳单元模拟混凝土喷层,采用三维非线性有限元技术,对洞室群的开挖支护动态过程进行了模拟计算。通过三维非线性有限元计算分析得到:洞室群动态开挖过程中围岩应力变形的分布规律,围岩塑性区的发展规律,锚杆受力变化情况。计算结果表明:整个开挖过程中,洞周围岩位移变化规律正常,量值较小,塑性区主要分布在洞室周边,围岩稳定性较好;但在洞室交叉口处围岩的变形较大,出现较大范围的塑性区,在此基础上提出了支护措施优化方案,并对优化方案的效果进行了评价。     

Evaluation of freshwater mussel relocation as a conservation and management strategy

The relocation of unionacean mussels is commonly used as a conservation and management tool in large rivers and streams. Relocation has been used to recolonize areas where mussel populations have been eliminated by prior pollution events, to remove mussels from construction zones and to re-establish populations of endangered species. More recently, relocation has been used to protect native freshwater mussels from colonization by the exotic zebra mussel Dreissena polymorpha. We conducted a literature review of mussel relocations and evaluated their relative success as a conservation and management strategy. We found that 43% of all relocations were conducted because of construction projects that were forced to comply with the Endangered Species Act 1973 and that only 16% were monitored for five or more consecutive years. Most (43%) relocation projects were conducted from July to September, presumably a period when reproductive stress is relatively low for most species and the metabolic rate is sufficient for reburrowing in the substrate. The mortality of relocated mussels was unreported in 27% of projects; reported mortality varied widely among projects and species and was difficult to assess. The mean mortality of relocated mussels was 49% based on an average recovery rate of 43%. There is little guidance on the methods for relocation or for monitoring the subsequent long-term status of relocated mussels. Based on this evaluation, research is needed to develop criteria for selecting a suitable relocation site and to establish appropriate methods and guidelines for conducting relocation projects.     

SPATIAL AND TEMPORAL WATER QUALITY VARIABILITY IN AQUATIC HABITATS OF A CULTIVATED FLOODPLAIN

The floodplains of lowland rivers contain diverse aquatic habitats that provide valuable ecosystem services but are perturbed when intensively cultivated. Hydrologic, water chemistry and biological (fish) conditions in five aquatic habitats along the Coldwater River, Mississippi, were measured for more than 4 years: the river, two severed meanders that functioned as backwaters, a managed wetland and an ephemeral channel draining cultivated fields. Off‐channel habitats were connected to downstream regions 0.10% to 32% of the dry season and 24% to 67% of the wet season. The median temperatures for the five monitored sites ranged from 18°C to 23°C, the median total solids concentration for all sites was 135 mg L^?1, the median total phosphorus was 0.29 mg L^?1 and the median total nitrogen was 1.56 mg L^?1. Chemical and physical water quality displayed strong seasonal differences between the wet winter/spring and the dry summer/fall periods so that temporal variation consisted of gradual seasonal trends superimposed on strong diurnal variations. All off‐channel habitats exhibited periods of hypoxia and temperatures >30°C during the dry season. Between‐site gradients of water and habitat quality were strongly coupled to water depth and runoff loading. The rehabilitation of one backwater by increasing water depth and diverting agricultural runoff was associated with improved water quality and fish species richness relative to an adjacent untreated backwater. The diversion of polluted runoff and the use of water control structures to maintain greater water depth were observed to be effective management tools, but the former reduces the water supply to habitats that tend to dry up and the latter reduces connectivity. Published in 2011 by John Wiley & Sons, Ltd.     

基于模型试验的河床砂砾石层基本特性研究

为了经济可靠地确定深厚覆盖层的基本特性参数,以大渡河双江口水电站坝基河床砂砾石层基本特性研究为工程背景,进行大尺寸模型试验,研究河床砂砾石层的旁压模量和动探击数随密度、级配以及上覆压力的变化规律。根据室内模型试验结果,结合现场旁压试验及钻孔试验成果,推断出坝址区河床砂砾石相关层位的密度,并依此进行砂砾石室内力学试验,获得设计所需力学参数。研究成果可为深厚覆盖层基本特性测试提供新的方法。     

Spatio‐temporal variation of gross CO2 and CH4 diffusive emissions from Australian reservoirs and natural aquatic ecosystems,and estimation of net reservoir emissions

Carbon dioxide (CO₂) and methane (CH₄) diffusive emissions were measured during two field surveys in Queensland and Tasmania, Australia, using the floating chamber method. Bubbling and degassing emissions in 2010 were estimated in Koombooloomba Dam reservoir using only inverted funnels and gas concentrations, respectively. A total of 14 reservoirs and 16 rivers and lakes were sampled from 2006 to 2010. Spatial variation was substantial within each water body, as well as between them. The main drivers of diffusive emission variation were physiographic region and climate, with a clear demarcation being observed between diffusive emissions from tropical Queensland and temperate Tasmania, and between the humid West Coast Range (Tasmania) and dry Central Plateau (Tasmania). Higher CO₂ and CH₄ diffusive emissions were observed during the dry season, when long water residence times would promote organic matter degradation. Estimated total gross emissions, including diffusive, bubbling and degassing emissions, for Koombooloomba Dam reservoir were about 1.5 × 10⁶ t CO₂eq km² per year, or 24 × 10⁶ t CO₂eq per year. This corresponds to a plant emission factor of 3.18 kg CO₂eq MWh^?1. Using an estimate of terrestrial emissions derived from literature data for the Tully River catchment area, rough estimated net emissions from the catchment area are about 44 kt CO₂eq per year, or 5.83 kg CO₂eq MWh^?1, which is in the lower range of the studied reservoirs.     

Automated system for removal and pneumatic transport of fly ash from electric precipitator hoppers

A system for removal and pneumatic transport of fly ash is examined, in which air pulses act on batches (pistons) of ash formed in a duct. Studies are made of the effect of several physical parameters on the force required to displace a piston of ash and these serve as a basis for choosing a system for removal and pneumatic transport of ash simultaneously from several hoppers of an electric precipitator. This makes it possible to separate the ash particles according to size without introducing additional components. Formulas are given for calculating the structural and dynamic parameters of this system and measurements of indirect dynamic parameters are used to calculate the input-output characteristics of the system. In order to optimize the system, configurations for summing several ducts into a single transport duct for pneumatic ash transport are proposed. Some variants of dry ash utilization and the advantages of producing of size-separated particles are considered. __________ Translated from élektricheskie Stantsii, No. 2, pp. 26–30 (2008).     

The flood pulse advantage and the restoration of river-floodplain systems

The ‘flood pulse advantage’ is the amount by which fish yield per unit mean water area is increased by a natural, predictable flood pulse. Evidence for this increase is presented from tropical and temperate fisheries. It is argued that increasing multispecies fish yield by restoring the natural hydrological regime is consistent with increasing production of other trophic levels and with restoration from ecological and aesthetic viewpoints. When applied to a river-floodplain system, this restoration would provide a large, self-sustaining potential for recreation, commercial exploitation, and flood control. An interim ‘natural flood pulse’ restoration approach is proposed for systems modified for navigation. This approach approximates the natural hydrological regime in a river reach and is intended as a first step in the long process of restoring the watershed.     

基于BP神经网络-马尔科夫链模型的隧道围岩位移预测

在隧道工程施工中,围岩位移预测起着很重要的作用。将BP神经网络-马尔科夫链模型引入到隧道围岩位移预测中来,通过对训练样本的学习,利用BP神经网络实现了对位移时间序列的滚动预测,同时得到了实测值与预测值的相对误差;在此基础上利用马尔科夫链对相对误差进行修正,有效地提高了预测结果的精度。并将该模型应用于某公路隧道拱顶下沉位移时序预测中,结果表明该模型具有精度高、科学可靠的特点,为隧道围岩变形的预测提供了新的途径。     

Short communication. Pipelines as a refuge for freshwater snails

In the lower River Murray, Australia, populations of gastropods have declined markedly over the past 40 years. Of the native fauna of about 18 species, only the ancylid Ferrissia petterdi remains common (but in patches), and another five species feature in sporadic local resurgences. Until recently the viviparid Notopala was thought to be extinct. The introduced physid Physa acuta is widespread, but in low numbers. The decline probably is associated with flow regulation, high turbidity and the introduction of common carp. Snail populations have persisted, however, in irrigation pipelines fed from the river, where they periodically cause blockages. This paper reports the discovery of the only known populaion of Notopala hanleyi in a pipeline where the inner wall accumulates microbial and other organic matter, providing high quality food for snails. In the Murray before regulation most of the periphytic biomass was probably microbial, as fluctuating water levels would have maintained littoral communities in a highly productive, early state of succession his postulated that, by stabilizing seasonal water levels, regulation has promoted the production of filamentous green algae, an inferior food source, and so displaced snail populations from the open aquatic environment.