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强震区的杨房沟拱坝的抗震安全问题为众多研究者所关注。本文用拉格朗日不连续变形分析(LDDA)模拟拱坝横缝,采用黏弹性边界作为吸能边界来模拟无限地基辐射阻尼,建立了拱坝地震自由场输入模型,进行了杨房沟拱坝动力响应分析,对辐射阻尼和拱坝横缝对坝体应力的影响、拱坝横缝在地震作用下的张开情况以及坝体静动综合应力进行了分析,得出了如下结论,考虑坝体横缝张开和地基辐射阻尼效应影响后,杨房沟拱坝的地震动力响应明显降低,大坝横缝张开度最大为6mm,在横缝止水可允许的变形范围之内,在进一步优化大坝体型基础上,杨房沟拱坝在设计地震作用下的抗震安全是可以保证的。 相似文献
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基于ABAQUS中的混凝土损伤塑性模型,分别建立了考虑地基辐射阻尼效应的有限元—无限元耦合模型和无质量地基模型,讨论高拱坝在设计地震作用下采用两种地基模型得到的应力、横缝开度、坝顶顺河向位移和损伤开裂情况。结果表明:无质量地基模型与无限元边界模型相比,坝体拱向和梁向应力最大值明显增加,增大了坝体的横缝开度和坝顶顺河向位移,同时坝体的损伤开裂情况更为严重。因无限元边界模型能考虑地基的辐射阻尼效应,能真实地反映坝体的地震响应,而无质量地基模型夸大了坝体的地震响应,故用无质量地基模型进行坝体的抗震分析是过于保守的。 相似文献
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杨房沟混凝土双曲拱坝最大坝高155 m,坝址所处地区地震烈度相对较大,为此,除了按DL5073—2000《水工建筑物抗震设计规范》的原则、方法和要求进行常规抗震分析外,同时还考虑坝址地形地质条件、计入地基辐射阻尼和横缝张开影响的三维非线性有限元法对大坝及基础进行动力分析,综合分析评价了大坝的抗震性能与抗震安全性。研究结果表明,杨房沟高拱坝在设计地震和校核地震作用下,坝体应力状况较好,坝体横缝最大张开度不会破坏横缝止水设施,满足设计要求。采取的抗震措施能够进一步提高拱坝的整体性和抗震性,杨房沟高拱坝的抗震安全是可以保证的。 相似文献
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陈林 《甘肃水利水电技术》2013,(8):31-33,42
比较了高低两种水位、不同地震荷载、无限地基辐射阻尼、地震自由场幅差相差对大岗山拱坝非线性动力响应的影响,以及各种工程抗震措施的抗震效果。由以上计算研究成果可以得出,大坝的地震动力反应较为强烈,但是通过计算分析,大坝的横缝开度、坝体应力和位移的量值仍在目前国内工程设计水平可以接受和控制的范围以内。通过有效的抗震工程措施,大岗山拱坝的抗震安全性是有保证的。 相似文献
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混凝土拱坝横缝对坝肩抗震稳定的影响 总被引:3,自引:0,他引:3
简单介绍了将刚体极限平衡法与考虑横缝的拱坝-地基系统有限元静动力分析相结合,将有限元时程分析的计算成果用于刚体极限平衡求解高拱坝坝肩块体抗滑稳定安全系数的基本思路和计算公式,并详细推导了模拟拱坝横缝动态张合效应的动接触力模型基本公式。最后又以两个实际工程为例,在考虑无限地基辐射阻尼作用的条件下,区分有、无横缝两种情况,在有限元静动力分析的基础上,用本文介绍了方法分别进行拱端推力、块体震力,以及块体动力安全系数的分析,通过这两种工况计算结果的对比,揭示拱坝横缝对坝肩抗震稳定的影响。 相似文献
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强震作用下高拱坝横缝张开非线性反应的研究 总被引:4,自引:0,他引:4
采用接触单元模拟拱坝横缝,对高拱坝在强震作用下横缝张开的非线性反应进行了系统的研究,首先,从横缝的最大张开度,坝体的应力分布及坝体的最大位移等不同角度研究了横缝模拟条数的最佳方案;进而研究了库水位变化对横缝张开度,坝体应力和位移的影响,研究结果表明:为了有效地反映在强震中横缝张开效应对拱坝应力状态的影响,在分析中至少需要模拟3条大体均匀布设的横缝;但是,为了能充分反映横缝的强震过程中张开的实际情况,则至少需要模拟21条横缝,随着库水位的增高,拱坝横缝在强震中的最大张开度逐渐减小。 相似文献
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高碾压混凝土拱坝横缝开度对拱坝安全的影响 总被引:2,自引:0,他引:2
考虑混凝土材料非线性和横缝接触非线性,对沙牌拱坝进行结构分析,研究横缝下游宽度变化对拱坝工作性态的影响。计算结果表明,横缝下游宽度达到2mm以上,坝体应力恶化,将会危害到拱坝的安全。 相似文献
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《给水排水》2014,(9)
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. 相似文献
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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。 相似文献
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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. 相似文献
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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。 相似文献
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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. 相似文献
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Mutlu Ozdogan Curtis E. Woodcock Guido D. Salvucci Hüseyin Demir 《Water Resources Management》2006,20(3):467-488
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. 相似文献
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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. 相似文献
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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. 相似文献