考虑土工膜缺陷的面膜坝渗透稳定性分析

为研究土工膜缺陷的面膜坝在库水位骤降情况下的渗流特性以及上游坝坡的稳定性,利用Geo-slope软件建立了破损土工膜有限元分析模型,对土工膜不同破损部位以及破损尺寸进行了渗流要素和稳定性分析。结果表明:土工膜破损位置越高,尺寸越大,浸润线抬升越高,渗漏量越大,但后者影响明显小于前者;当库水位高程降落至土工膜破损高程时,存在一个浸润线突然下降的“突变”初始稳定安全系数随着土工膜缺陷位置的变高和尺寸的变大而变小,安全系数总体上呈现先下降,后趋于稳定的规律,但在库水位高程经过土工膜缺陷处,存在一个突然上升的过程。研究成果为面膜坝运行过程中的稳定性评价和治理提供了参考。     

平原水库复合土工膜缺陷渗漏影响因素数值分析

使用Flac3d数值模拟软件,以南水北调东线大屯水库为原型,建立平原水库复合土工膜缺陷渗漏数值计算模型,分析缺陷孔径、位置、水头高度及多缺陷联合作用对平原水库实际工程渗漏量的影响。结果表明:数值计算结果和室内试验结果吻合度较高,可用于实际工况分析;复合土工膜缺陷的数量和水头高度是影响复合土工膜缺陷渗漏的主要因素,其次为缺陷尺寸、缺陷间距和缺陷位置;复合土工膜缺陷尺寸较小和距坝脚较远时对复合土工膜缺陷渗漏量影响较小;复合土工膜缺陷渗漏量随缺陷数量和库水位的增加呈线性增长的趋势,当缺陷距坝脚小于100 m,且缺陷尺寸大于10 mm,同时缺陷间距较小时,应重点排查修补。     

平原水库土工膜防渗特性分析

复合土工膜防渗措施是解决平原水库渗漏问题的有效手段。为了研究平原水库土工膜防渗特性,以山东省清源湖水库为例,采用数值模拟与现场实测相结合的方法,建立了基于饱和-非饱和渗流微分方程的土工膜防渗围坝渗流有限元分析模型,并将计算结果与实测数据进行了对比。研究表明铺设土工膜防渗后,非饱和区域显著增加,忽略非饱和区域会使得渗漏量计算值偏小、浸润线及溢出点高度计算值偏低,令设计者低估渗漏的严重程度,不利于坝体的渗流稳定;土工膜缺陷因素(如缺陷的位置、尺寸、数目及与其下垫层的接触情况)对渗漏量和围坝浸润线亦有较大影响;土工膜缺陷及土工膜与下垫层的接触情况主要取决于施工质量,在施工期对土工膜缺陷进行严格控制,可有效减少渗漏量,对平原水库的安全运行具有十分重要的意义。     

土体干密度对防渗土工膜膜下气场的影响

本文采用室内试验方法模拟水库现场实际情况,分析平原水库库盘土工膜防渗情况下,库底土体干密度对土工膜膜下气场的影响.结果表明:膜下土体干密度对膜下气场影响明显,干密度越大,库区膜下气场产生速率及气压越小.建议在平原水库库底土工膜防渗时要做好库区基底碾压,尽量选用干密度较大的土壤.     

土工膜缺陷对土石坝渗流特性的影响及控制措施

由于土工膜因缺陷导致的渗漏问题可能对土工膜防渗土石坝工程安全造成隐患,为此模拟不同的土工膜缺陷大小和位置,分别采用剔除单元法和渗透系数放大法对存在缺陷的土工膜坝面防渗土石坝进行饱和-非饱和三维渗流场有限元数值仿真计算,分析土工膜不同缺陷条件下大坝整体及局部渗流场变化规律。计算结果表明:土工膜缺陷渗漏仅对缺陷附近坝体局部渗流场分布产生较大影响,对大坝其他部位影响不大;土工膜缺陷位置越低,缺陷处水头越大,缺陷渗漏量增加越明显,并使缺陷处膜后坝体浸润线局部抬高。最后,针对土工膜缺陷渗漏提出了若干工程设计控制措施。     

土工膜防渗平原水库膜下气场数值模拟

以多相孔隙介质理论为基础推导了考虑孔隙中水气二相流的非饱和土固结理论方程,在一定的简化假设基础上编写了相应的有限元耦合计算程序。针对某土工膜全库盆防渗的平原水库进行了不同地下水位与库水位组合方案的三维有限元计算,通过整理库底和过渡平台两处膜下气压与地下水位及库水位变化关系曲线分析了土工膜下气压变化规律。计算结果表明:地下水位快速上升会引起膜下气压迅速增大,使得土工膜的气胀成为可能;当地下水位与土工膜间距小于1m时,膜下气压会随着库水位上升迅速增大。     

随机多缺陷条件下土工膜防渗土石坝渗漏特性

由于土工膜缺陷渗漏可能对土工膜防渗土石坝的防渗安全性造成隐患,采用饱和-非饱和渗流有限元理论,对坝面防渗土工膜多缺陷随机分布下的典型土石坝进行三维渗流场有限元模拟,合理考虑土工膜缺陷的数量、类型、位置、大小及其分布,重点分析土工膜的渗透量和缺陷渗漏量及膜后浸润面的变化规律。结果表明:与单缺陷条件下大坝渗流特性相比,坝面完好部分土工膜的渗透量变化不大,但多缺陷引起的渗漏量明显增大,导致大坝的总渗流量大幅增加。多缺陷会引起膜后坝体浸润面整体抬升,但局部浸润面高度变化与缺陷位置和数量明显相关,所在剖面缺陷位置越低,数量越多,浸润面抬升越明显。另外,膜后垫层水头局部分布规律与相邻缺陷渗漏的交叉效应相关。     

库水位下降速率对土石坝稳定性分析研究

库水位下降过程中,坝体黏性土对水份的吸力作用使得黏性土体内的水份不能及时消散,造成黏性坝体内水位高于库内水位,所发生现象对坝坡渗流、稳定与应力均产生较大影响.以大禾田水库为例,基于饱和-非饱和渗流理论,采用二维有限单元方法,分析库水位下降后的渗流稳定、应力及水压荷载作用下位移变形,分析库水位下降速率对土石坝稳定性的影响,研究结果对水库调度运行管理有一定的指导作用.     

先锋岭水库水位下降期坝坡稳定分析

先锋岭水库水位下降期,由于坝体内孔隙水压不能及时消散的影响,坝体内的水无法排出,久而久之其水位便会高于库内水位。长期的高水位运行容易降低坝坡的稳定性,导致坝坡应力失去平衡而出现失稳情况,给水库的安全运行埋下安全隐患。为了能够确定先锋岭水库加固后大坝的坝坡稳定安全系数,分析了库水位下降期渗流稳定、坝坡稳定情况,并通过采用极限平衡法与有限元法对库水位下降期坝坡稳定性进行计算。结果表明,当渗透比降小于0.3 J时,坝坡稳定安全系数会随着库水位的下降变得稳定;当渗透比降大于0.3 J时,坝坡稳定安全系数会随着库水位的下降而下降。本次坝体水位骤降时的渗透比降是0.292 J,小于允许渗透比降,其背水坡、迎水坡在多种工况下的抗滑安全系数均满足设计规范要求值,并不存在不利水位。     

瀑河水库坝基渗流稳定分析及处理措施

瀑河水库自建库以来,多次发生坝基渗漏、坝后管涌和下游沼泽化等渗流破坏现象。通过对工程地质的分析,提出引起坝基渗流破坏的几处薄弱地带。经过渗流稳定理论计算,预测在高库水位条件下主副坝均存在渗流破坏的可能性。为消除大坝可能出现的渗流稳定安全隐患,建议在坝前增设土工膜水平防渗;在主坝段增设坝后贴坡排水。     

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.     

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。     

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。     

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.     

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.     

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.