海工码头结构混凝土耐久性检测与评估

为研究环境因素对结构混凝土耐久性的影响,现场检测了宁波某海工码头工作平台不同结构区域的结 构混凝土耐久性能. 检测结果表明碳化深度和钢筋保护层厚度的特征值与设计值的比值为大气区>水位变动区 >水下区;混凝土表面氯离子浓度和碱含量为水下区>水位变动区>大气区;表观氯离子扩散系数为水位变动区> 水下区>大气区. 大气区混凝土易受CO2 侵蚀而导致混凝土钢筋保护层劣化. 有害介质氯离子与CO2 共同侵蚀 导致水位变动区混凝土钢筋锈蚀和钢筋保护层劣化. 作业时间有限和环境恶劣降低了水下区混凝土对钢筋的 保护能力,导致钢筋锈蚀速度和钢筋保护层劣化加快.     

钢筋锈蚀率的概率模型及时变可靠度分析

氯离子引起的钢筋锈蚀是导致钢筋混凝土结构性能劣化的主要原因,因此有必要对钢筋锈蚀率的计算进行详细研究。考虑钢筋锈蚀过程中各影响因素的不确定性,将钢筋初锈时间和保护层开裂时间作为随机变量,首先分3种情况建立钢筋锈蚀率的计算模型;然后通过Monte Carlo模拟对锈蚀率进行概率分析,确定锈蚀率的概率分布类型和统计参数,最后根据收集的试验数据建立钢筋混凝土受弯构件剩余承载力与钢筋锈蚀率的关系,对受腐钢筋混凝土受弯构件进行时变可靠度分析。研究表明:钢筋锈蚀率服从正态-正态双峰分布;暴露时间越长,钢筋未锈蚀和混凝土保护层未开裂的概率越小;构件可靠度随时间的增加明显降低。     

浅谈钢筋混凝土构件表面防护与剥蚀修补

调查与研究表明,混凝土碳化、氯离子侵蚀是导致钢筋混凝土构件钢筋锈蚀的主要原因,钢筋锈蚀使构件产生裂缝、混凝土剥落等表层剥蚀破坏。我省在加固水闸公路桥、丁作桥等水上构件时,采用HS环氧厚浆涂料防碳化、防氯离子侵蚀表面封闭处理,对构件表面剥蚀破坏部位用苏水ME-4高性能修补砂浆修补．均取得良好效果。     

混凝土保护层锈胀裂缝扩展规律试验研究

基于通电加速腐蚀方法,研究了4种试件的表面开裂时间和表面裂缝宽度随时间的演化。开裂初期,表面裂缝宽度随时间缓慢增大,当裂缝宽度达到一定值后,表面裂缝宽度随时间迅速增大,最后呈稳定扩展趋势;纵向钢筋的锈蚀并不均匀,钢筋面向保护层一侧的钢筋表面锈蚀较为严重。     

海工混凝土氯离子分布概率模型分析与应用

在海工混凝土结构中,由于氯离子侵蚀导致的钢筋锈蚀问题十分普遍。为准确判断钢筋初锈时间,预测结构耐久性劣化规律,在现有氯离子扩散模型的基础上,基于蒙特卡罗理论,利用MATLAB软件对钢筋周围氯离子浓度分布进行随机抽样模拟。结果表明一定时间段内（10年、50年、100年）钢筋周围氯离子浓度服从对数正态分布,并提出判断钢筋锈蚀的概率模型,以概率方法判断钢筋锈蚀,其可靠性将大大增加。结合该模型对连云港港区现场服役混凝土构件进行了氯离子含量预测,现场取粉试验结果基本符合该模型分布,其均值吻合较好,并对港区混凝土结构耐久性使用寿命失效概率进行了风险评估。     

东海环境下混凝土中Cl~-渗透性能及对钢筋锈蚀的影响研究

以实际海洋工程结构为依托,通过实海暴露试验和实验室性能检测,对服役时间、裂缝宽度、保护层厚度和Cl~-浓度影响钢筋混凝土结构的腐蚀劣化进行了研究。结果表明,混凝土初期氯离子渗透速度较快、后期明显减小;裂缝可作为氯离子渗透的有效途径;而保护层厚度越大,外界腐蚀性介质侵入越困难;氯离子可有效增强混凝土孔隙液的导电能力,导致钢筋腐蚀;且随氯离子浓度增大,钢筋自腐蚀电流密度增大并逐渐趋于稳定。     

人工气候环境下水工混凝土钢筋初始锈蚀时间预测

根据人工气候环境下的混凝土侵蚀试验测得的混凝土中氯离子质量分数,分别研究了腐蚀24 d,40 d,80 d,120 d和160 d后混凝土的氯离子扩散参数,基于Fick第二定律和Monte-Carlo法模拟了混凝土中钢筋的初始锈蚀时间。结果表明,在人工气候环境下混凝土保护层有效厚度对水工混凝土钢筋初始锈蚀时间的影响较大。     

混凝土构件锈蚀胀裂时的钢筋锈蚀率

本文建立了由于钢筋锈蚀导致的混凝土保护层胀裂时的钢筋混凝土构件的力学模型，应用弹性力学理论得到了混凝土保护层胀裂时的钢筋锈蚀率的解析表达式，并讨论了与混凝土保护层胀裂时的钢筋锈蚀率相关的各个影响因素，得到以下结论：随着混凝土保护层厚度和混凝土等级的增加，混凝土胀裂时的钢筋锈蚀率会增大；混凝土内钢筋直径的减小，也会导致混凝土胀裂时钢筋锈蚀率的增加；不同的钢筋锈蚀产物，有着不同的铁锈膨胀率，随着铁锈膨胀率的减小，混凝土保护层胀裂时的钢筋锈蚀率增大；而铁锈的名义弹性模量和名义泊松比对混凝土保护层胀裂时的钢筋锈蚀率影响很小。     

海工环境混凝土中氯离子扩散敏感性分析

混凝土结构耐久性问题是当今世界普遍关注的问题。由于氯离子侵蚀,导致钢筋锈蚀,使结构发生早期破坏,丧失了结构的耐久性能,已成为实际工程中的重要问题。基于Fick第二定律,分别考虑表面氯离子浓度、温度、水灰比、初始氯离子含量,计算氯离子扩散。敏感性分析表明表面氯离子浓度、温度、水灰比对混凝土中氯离子扩散影响较大,初始氯离子含量影响较小。     

海洋生物附着对混凝土结构耐久性能影响

为研究海洋生物对混凝土结构的影响机理,分别对海洋动物、植物以及微生物3种类型的海洋生物进行分析,重点讨论3种生物对混凝土结构的腐蚀机理和增强机理,并对其利用和防治进行了详细论述。通过某码头混凝土桩的现场长期暴露试验,研究混凝土内部的氯离子浓度、混凝土电阻率及钢筋电位的分布规律。结果表明,浪溅区的表面氯离子含量低于潮汐区,而混凝土氯离子扩散系数较为接近。贝类生物的聚集作用对混凝土抗氯离子性能具有正负效应:一方面,贝类覆盖区混凝土的表面氯离子含量较低,表明贝类的存在有利于降低混凝土表面氯离子的聚集,在混凝土表面起到物理保护作用,一定程度上有利于阻止氯离子的入侵;另一方面,贝类覆盖区混凝土内氯离子扩散系数大于光滑表面区,贝类的存在可能导致混凝土本体发生变化,削弱了混凝土自身的抗氯离子侵蚀能力,加快了氯离子在混凝土内部的传输。有贝类聚集时,混凝土表面电阻最低,且混凝土内部钢筋的腐蚀电位较负,表明该区域混凝土内部钢筋的腐蚀风险最高,该海域贝类存在可能对混凝土的耐久性能造成不利影响。     

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.     

Serial discontinuities in a Rocky mountain river. I. Distribution and abundance of plecoptera

Samples were taken year-round at eleven sites along the altitudinal profile (2900-1400 m a.s.l.) of the Gunnison River, a 329 km tributary of the Colorado River, to document the distribution of the Plecoptera and to evaluate responses to hypolimnial-release dams in the headwaters and middle reaches. Twenty-two species were present, with the greatest species richness occurring in an unregulated segment upstream of the middle reach dams; average nymphal biomass over the study period (175 organisms, 395 mg dry mass m^?2) was also greatest in this segment. Only four species (58 organisms, 48 mg m^?2) were present in the tailwaters of the headwater dam and values were greatly reduced (nine species; 35 organisms, 180 mg m^?2) below the middle reach dams. The stonefly community recovered ca. 80 km downstream from the last dam (15 species; 244 organisms, 250 mg m^?2), apparently in response to natural resetting of environmental conditions corresponding to those above the middle reach dams. At the most downstream site (11) only four species (four organisms, 16 mg m^?2) were present. The observed distributional pattern is a classic serial discontinuity in response to hypolimnial stream regulation in a temperate latitude river.     

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。     

Impacts of Microcystis on algal biodiversity and use of new technology to remove Microcystis and dissolved nutrients

Cyanobacteria often dominate eutrophic lakes, outcompeting green algae that are required by fish and zooplankton. This study was undertaken to ascertain the impact of the cyanobacterium, Microcystis, on algal biodiversity. Under laboratory conditions, we found that the presence of Microcystis decreased phyla richness by 58%, phyla evenness by 47%, genera richness by 66% and genera evenness by 51%. Analysis by mixed anova s demonstrated a significant interaction between treatment and time and confirmed a significant reduction in richness and evenness of phyla and genera. We also conducted a phosphate restriction assay on the algae in Mason Lake (Irvine, CA, USA) and found that the threshold needed for algal growth there was 0.02 mg L^?1 PO₄. A pilot study was then conducted to test the effectiveness of the Blue Pro? water treatment facility in removal of this colonial organism from Mason Lake, in addition to removal of dissolved nutrients required for its growth. We measured a 97% reduction in Microcystis cells, a 72% reduction in chlorophyll‐a, and a 96% reduction in phosphate after just one 10 min cycle through the unit. Our study demonstrated that removal of Microcystis colonies may allow green algae to increase in numbers. This may improve algal biodiversity, which will benefit zooplankton and fishes.     

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。     

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。     

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.     

簸箕李引黄灌区水沙分布及优化调度的经验

灌区利用水沙观测所取得的资料和试验数据，运用水沙运动力学理论，总结分析和揭示了灌区水沙分布的规律和特点。在此基础上，结合灌区的实际运行情况，围绕减少骨干渠道的淤积进行探讨、研究，进而，优化水沙调度方案。该方案实施后，骨干渠道减旅伴效果明显，取得了成功的经验。