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Several issues to be considered for long-term
better behavior of concrete gravity dams
Jinsheng JIA,
Front. Struct. Civ. Eng.. 2010, 4 (1): 40-46.
https://doi.org/10.1007/s11709-010-0006-5
Along with economic, social quick development and urbanization, dams and reservoirs are of strategic importance for flood control, water supply, electricity production, irrigation, etc., both for developed countries and for developing countries. Climate change is a new challenging issue to be considered which will speed up the development of hydropower in developing countries. More and more attention will be paid on the long-term better behavior of dams to guarantee the safety of the people involved and the better development of the world. There are about 50000 old dams in the world and a lot of them have been completed and operated for more than 50 years. However, how do we evaluate the dams’ safety? How do we make the decision to do rehabilitation work or to rebuild a new dam based on evaluation results? The life span and the real safety status of old dams becomes a challenging task for the dam society, especially for China because it has more than 6000 dams to be evaluated and rehabilitated within the next few years. Based on the investigation of the Fengman gravity dam, which is 91.7 m high, operated since 1943 and suffered uplift pressure, freeze and thaw problems, etc., discussions on the life span evaluation of old concrete gravity dams have been made. The reasonable coefficient of dam safety has been discussed. The social decision for the final choice after comprehensive studies has been introduced.
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Development of an integrated modeling system
for improved multi-objective reservoir operation
Lei WANG, Cho Thanda NYUNT, Toshio KOIKE, Oliver SAAVEDRA, Lan Chau NGUYEN, Tran van SAP,
Front. Struct. Civ. Eng.. 2010, 4 (1): 47-55.
https://doi.org/10.1007/s11709-010-0001-x
Reservoir is an efficient way for flood control and improving all sectors related to water resources in the integrated water resources management. Moreover, multi-objective reservoir plays a significant role in the development of a country’s economy especially in developing countries. All multi-objective reservoirs have conflicts and disputes in flood control and water use, which makes the operator a great challenge in the decision of reservoir operation. For improved multi-objective reservoir operation, an integrated modeling system has been developed by incorporating a global optimization system (SCE-UA) into a distributed biosphere hydrological model (WEB-DHM) coupled with the reservoir routing module. The new integrated modeling system has been tested in the Da River subbasin of the Red River and showed the capability of reproducing observed reservoir inflows and optimizing the multi-objective reservoir operation. First, the WEB-DHM was calibrated for the inflows to the Hoa Binh Reservoir in the Da River. Second, the WEB-DHM coupled with the reservoir routing module was tested by simulating the reservoir water level, when using the observed dam outflows as the reservoir release. Third, the new integrated modeling system was evaluated by optimizing the operation rule of the Hoa Binh Reservoir from 1 June to 28 July 2006, which covered the annual largest flood peak. By using the optimal rule for the reservoir operation, the annual largest flood peak at downstream control point (Ben Ngoc station) was successfully reduced (by about 2.4m for water level and 2500m3·s−1 for discharge); while after the simulation periods, the reservoir water level was increased by about 20m that could supply future water use.
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Features of seismic hazard in large dam projects
and strong motion monitoring of large dams
Martin WIELAND,
Front. Struct. Civ. Eng.. 2010, 4 (1): 56-64.
https://doi.org/10.1007/s11709-010-0005-6
Earthquakes can affect large dam projects in many different ways. Usually, design engineers are focussing on ground shaking and neglect the other aspects. The May 12, 2008 Wenchuan earthquake has damaged 1803 dams and reservoirs, and 403 hydropower plants with an installed capacity of 3.3GW. Among these dams were the 132-m-high Shapai RCC arch dam and the 156-m-high Zipingpu concrete face rockfill dam. These recently completed dams are dam types which, up to now, have not experienced strong ground shaking. The widespread mass movements have caused substantial damage to dams and surface powerhouses in Sichuan. The different features of earthquake hazard are presented, i.e., ground shaking, faulting and mass movements. It is proposed to prepare project-specific safety plans for all dams, which consist of a matrix where the possible hazards and the corresponding countermeasures are listed. The earthquake behaviors of the Sefid Rud, Zipingpu and Shapai dams, which, in the past, have experienced strong ground shaking from nearby earthquakes, are discussed. Finally, the need for strong motion instrumentation of large dams is discussed. It is proposed that major dams with large damage potential, dams located in areas of high seismicity, and dams showing signs of abnormal behavior be equipped with strong motion instruments.
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Analysis of catchment evapotranspiration at different
scales using bottom-up and top-down approaches
Xiangyu XU, Dawen YANG,
Front. Struct. Civ. Eng.. 2010, 4 (1): 65-77.
https://doi.org/10.1007/s11709-010-0002-9
Physically-based hydrological models are used to predict catchment water balance through detailed simulation of hydrological processes at small temporal and spatial scales. However, annual catchment water balance can also be easily and simply predicted using lumped conceptual model. Comparison between physically-based hydrological models and lumped conceptual models can help us understand the dominant factors on catchment water balance at different scales. In this paper, a distributed physically-based hydrological model (i.e., bottom-up approach) and a simple water-energy balance model (i.e., top-down approach) are used to predict actual evapotranspiration in nine sub-catchments, and the whole basin of the Luan River in northern China. Both simulations give very close values of annual evapotranspiration and show the same complementary relationship between actual and potential evapotranspiration at annual time scale. From the analysis at different time scales through comparison of the top-down and the bottom-up methods, it is shown that the annual catchment evapotranspiration is controlled mainly by annual precipitation and potential evapotranspiration, and the variability of soil water and vegetation becomes more important at a smaller time scale in the study areas. It is also known that the relationship between potential and actual evapotranspiration shows a highly nonlinear relationship at the annual and catchment scale but can be simplified to a linear relationship at hourly temporal and hillslope scales, which is commonly used in the physically-based hydrological models.
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Hypoplastic constitutive modeling of wetting
deformation of weathered rockfill materials
Erich BAUER, Zhongzhi FU, Sihong LIU,
Front. Struct. Civ. Eng.. 2010, 4 (1): 78-91.
https://doi.org/10.1007/s11709-010-0011-8
The wetting deformation of weathered rockfill materials has been attracting growing attention from both engineers and scientists. The importance of realistic predictions of wetting deformations for high earth and rockfill dams is a strong motivation to establish a suitable constitutive model. Recently, the hypoplastic constitutive model by Gudehus and Bauer was extended by introducing solid hardness depending on the state of weathering. The extended model takes into account the influence of the current density, the effective stress state, the rate of deformation, and the time dependent process of degradation of the solid hardness. In the present paper, the performance of this model is evaluated by comparing numerical simulations with experiments obtained from a water sensitive rockfill material. In particular, triaxial compression paths and creep deformation under deviatoric stress states are considered. Finally, the constitutive model proposed is used to study the influence of a degradation of the solid hardness on the long term behavior of a hypothetical fill dam.
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11 articles
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