无黏结材料颗粒流模型的宏细观参数关系研究

基于颗粒流(PFC2D/3D)模型的细观离散元方法是近些年来兴起的一种新的岩土数值计算方法,在岩土工程非连续介质领域中发挥着重要作用,但由于该类模型宏细观参数关系的复杂性,使其在实际工程应用中受到限制。在前人研究的基础上,以无黏结颗粒材料为例,采用4因素3水平正交试验方法设计了9类试样,并各自在3种侧压下进行双轴试验,以探求细观参数不同组合对介质宏观特性的影响,从而避免了控制变量法固定某些参数的局限,更加科学地分析了细观参量对宏观特性影响的敏感程度,并据此提出该类材料宏细观参数匹配的调整原则。最后利用人工神经网络实现了该类材料宏细观参数之间的互演计算,以供PFC模型在实际岩土工程计算时参考。     

管线渗漏引发地面塌陷的DEM-CFD耦合数值模拟

基于流固双向耦合原理,在离散元软件PFC3D基础上使用DEM(离散元)与CFD(计算流体动力学)耦合模块,考虑流体高速渗流时的流体压力梯度力对流固耦合过程的影响,建立了土颗粒与流体双向耦合作用下的细观数值模拟力学模型,针对渗流发生和发展过程中土体力学性能和水力性质进行了研究,从而定性地揭示了地表塌陷过程的演化规律与灾变机理。结果表明,流体高速渗流时,流体压力梯度力数值大于拖曳力,且土颗粒半径越大,流体压力梯度力越大;地表塌陷过程中土体塌陷模式呈圆锥形变化。     

砂土管涌－滤层防治的离散元数值模拟

结合小比尺细观模型试验,利用并开发基于离散元理论的颗粒流程序(PFC3D),充分考虑流固耦合作用,建立渗流理论模型,对不同层间系数下砂土管涌的基料-滤层系统进行离散元数值模拟,跟踪记录渗流过程中砂样运动、流失量、孔隙率、渗透系数、颗粒间接触力、水力梯度等参数的动态变化过程,从细观角度揭示管涌发展过程中颗粒的运动特性和滤层防治机理。数值模拟结果表明,层间系数D15/d85s大小是滤层是否有效的关键因素;在有效的层间系数下,随着水力梯度的加大,基料的细颗粒运动并进入滤层,在滤层-基料交界处存在的自滤现象。模拟结果与有关的模型试验结果吻合较好,一定程度上验证了该数值方法的可行性和合理性。本文所揭示的结果有益于对砂土管涌和滤层防治机理的更深入研究。     

颗粒材料定向剪切特性的空心圆柱离散元模拟

基于PFC3D离散元模拟平台构建空心圆柱型数值模型,研究了固定主应力方向条件下颗粒材料数值试样的定向剪切宏细观力学响应,重点分析了大主应力方向角对试样单调剪切特性的影响。数值建模中,采用"分离式簇墙"技术近似模拟室内试验橡皮膜的柔性边界效应,开发了顶部扭矩层颗粒旋转速度的"动态更新法"并较好地实现了剪应力的施加。结果表明,离散元数值模型能够较好地还原室内空心圆柱砂样定向剪切试验的应力路径和应力—应变响应;大主应力方向角α的变化显著影响数值试样的剪切强度,α=60°试样的峰值内摩擦角最低,且数值模拟得到的规律与已有的实际砂土室内试验规律相一致;数值试样剪切带的宏观演化在细观上可由试样内部局部孔隙比和配位数的变化规律来表征。     

砂土管涌－滤层防治的离散元数值模拟

结合小比尺细观模型试验，利用并开发基于离散元理论的颗粒流程序（PFC3D），充分考虑流固耦合作用，建立渗流理论模型，对不同层间系数比下砂土管涌的基料-滤层系统进行离散元数值模拟，跟踪记录渗流过程中砂样运动、流失量、孔隙率、渗透系数、颗粒间接触力、水力梯度等参数的动态变化过程，从细观角度揭示管涌发展过程中颗粒的运动特性和滤层防治机理。数值模拟结果表明，层间系数D15/d85s大小是滤层是否有效的关键因素；在有效的层间系数下，随着水力梯度的加大，基料的细颗粒运动并进入滤层，在滤层－基料交界处存在的自滤现象。模拟结果与有关的模型试验结果吻合甚好，一定程度上验证了该数值方法的和可行性和合理性。本文所揭示的结果有益于对砂土管涌和滤层防治机理的更深入研究。     

初始组构影响砂土液化势的细观数值模拟研究

本文基于PFC2D椭圆颗粒单元的二次开发，通过制备三种不同初始颗粒定向的数值试样，分别为随机定向（R试样）、水平定向（H试样）和竖直定向（V试样），研究了初始组构对砂土液化势的影响。数值试验采用常体积（面积）循环等应变幅加荷条件，试验过程在对比分析三种不同颗粒定向试样液化宏观力学响应的同时，从颗粒尺度层面探讨了不同颗粒定向试样的初始组构特征，揭示了初始组构影响砂土液化势的细观力学机理。结果表明，颗粒规则定向的试样其抗液化强度要高于随机定向试样，在细观机理上不仅与不同颗粒定向试样的初始平均接触数有关，而且与孔隙形态和孔隙率的分布密切相关；砂土的液化过程是一个组构各向异性的演化过程。     

初始组构影响砂土液化势的细观数值模拟

基于PFC2D椭圆颗粒单元的二次开发,通过制备3种不同初始颗粒定向的数值试样,分别为随机定向（R试样）、水平定向（H试样）和竖直定向（V试样）,研究了初始组构对砂土液化势的影响。数值试验采用常体积（面积）循环等应变幅加荷条件,试验过程在对比分析3种不同颗粒定向试样液化宏观力学响应的同时,从颗粒尺度层面探讨了不同颗粒定向试样的初始组构特征,揭示了初始组构影响砂土液化势的细观力学机理。结果表明,颗粒规则定向的试样其抗液化强度要高于随机定向试样,在细观机理上与不同颗粒定向试样的初始平均接触数有关,砂土的液化过程是一个组构各向异性的演化过程。     

孔隙介质渗流过程诱发声发射信号特征研究

在不破坏结构情况下,利用声发射(AE)监测技术探究不同流速下间断级配颗粒介质运动规律,以及孔隙渗流过程声发射信号变化规律。通过渗流过程中由小颗粒介质位移产生的声发射信号和PIV技术相结合进行分析。结果表明：小颗粒介质数量一定时,流速较大的试验组AE事件数更多,即振铃计数更大、频谱重心更高;水流量相近时,试验中小颗粒介质含量直接影响AE事件数量,即含砂量较大的试验组AE事件数更多;含有小颗粒介质情况下,水流量越大小颗粒运动速度越快同时AE初始信号强度越大。研究表明：声发射监测技术能较好地反映孔隙渗流中颗粒介质的运动,为孔隙介质渗流过程中的小颗粒搬运监测和堤坝管涌预警提供一定的研究基础。     

粘性土室内平面应变试验的颗粒流模拟

作为颗粒流理论实际应用的前期可行性研究，针对具有凝聚力的内摩擦材料粘性土进行了室内平面应变试验结果的颗粒流仿真。对三维颗粒流数值仿真技术(PFC2D)的4组数值仿真结果和粘土试样室内平面应变试验的实测曲线进行了对比，研究表明利用颗流理论所建立起来的PFC2D数值仿真试验模型是能够通过改变计算模型中颗粒单元的性质，以及颗粒集合体的级配特征等给出与真实材料土工试验类似的本构行为的，这种可行性最根本的意义在于基于颗粒流理论的数值仿真试验能够突破常规土工试验在仪器设备能力、试验条件上的局限性，对实际土样的本构行为做出理论方面的预测。此外针对颗粒流仿真试样的细观力学特征与物理试样宏观力学响应之间的关系进行了参数研究，并揭示了一些规律。     

重力条件下散体颗粒堆积特性研究

为分析散体颗粒堆积过程中颗粒形态、摩擦作用对其堆积特性的定量影响,利用PFC3D离散元软件,对重力作用下散体颗粒体系的变动过程进行三维模拟,研究颗粒细观特征对散体颗粒堆积特性的控制作用,分析颗粒接触度均值距离对相关数据的揭示意义。结果表明:摩擦系数、几何形态对颗粒重力堆积体系的孔隙比、配位数等关键特性影响显著;散粒体骨架颗粒形态对颗粒堆积特性的控制作用更强;颗粒接触度均值距离能够削弱算法误差影响,可有效揭示摩擦系数、颗粒形态对散粒体堆积特性的控制作用。经研究可知,颗粒接触度均值距离对颗粒堆积特性的刻画,比孔隙比更为合理、适当。     

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.     

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.     

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。     

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.     

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.     

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.