Introduction to dynamics of stone arches     

Paolo Clemente 《地震工程与结构动力学》1998,27(5):513-522

The dynamic analysis of stone arches, made up of rigid voussoir laid dray, can be performed in two phases. First of all the value of the horizontal acceleration necessary to turn the structure into a mechanism and the corresponding mechanism must be determined. Then the dynamic behaviour of such a mechanism under a given acceleration time history can be studied. The first step is a static matter. The second one requires the solution of the non-linear equation of motion of the one-degree-of-freedom system in which the arch is turned. In this paper an iteration procedure is proposed to find out the mechanism. Then the structural behaviour of the mechanism is analysed. Both free and forced vibrations are investigated and the study is limited to the first-half cycle of vibration. Damping is not considered and sliding between the blocks at the hinge sections is not allowed. © 1998 John Wiley & Sons, Ltd.  相似文献   

Predicting dam-related downstream geomorphic response with widely available stream gauge data: A case study of the Godavari River Basin,India     

Joy Sanyal  Priyanka Dasgupta  Shinjiro Kanae 《Singapore journal of tropical geography》2020,41(2):284-298

Dam-related downstream adjustments of riverbeds are normally investigated by analysing the trend in sediment supply and high flow events during the pre- and post-dam periods. The required data for existing predictive models is not measured at river gauges, which limits the application of these tools. We derived the frequency of sediment-transporting streamflow events (T*) and upstream sediment supply (S*) in the pre- and post-dam periods with widely available gauged records and predicted changes in the downstream riverbed by adapting an existing model. Ten gauging stations in the Godavari River Basin, India, located downstream of dams, were chosen as study sites. Annually surveyed cross-sections at each site validated the accuracy of the predicted dam-related downstream changes. Then, a regression equation (R² = 0.75) was established between T*/S* (independent variable) and changes in the downstream bed elevation (dependent variable) for the Godavari Basin. We recommended that similar local empirical equations be formulated for larger river basins. Models of large-scale rainfall-runoff and sediment transport processes that can account for the influence of dams, such as the Soil & Water Assessment Tool, can be paired with the proposed regression equation to estimate dam-related downstream erosion and deposition with globally available data.  相似文献   

GRAVEL SLUICING IN ALPINE RUN-OF-RIVER HYDROPOWER PLANTS     

Helmut SCHEUERLEIN Institut flier Wasserbau  Univeristy of Innsbruck  Technikerstn . A- Innsbruck  Austria. 《国际泥沙研究》2001,16(2)

1 INTRODUCTIONNdsral rivers entering reservoirs carry also sediment, partly as bedload and patly in suspension. At theentrance of the reservoir flow velocity is considerably reduced and the capability of sediment transport isdrashcally fading. Bedload maerial is deposited totally at the reservoir entrance fondng a delta, material...in suspension is cAned further intO the reservoir ulh.. it is partly deposited and partly dischargedthrough the dam towards downstreaxn (depending on the trapp…  相似文献   

淮河大堤土体工程地质特性及采动裂缝研究   总被引：1，自引：0，他引：1  

李文平  于双忠 《煤田地质与勘探》1992,20(2):47-50

淮河下采煤,使地面大堤土体中出现了许多采动裂缝,普遍认为裂缝的存在对大堤与河下采煤安全构成很大威胁。以土体工程地质特性研究为基础,采用试验和力学分析方法,分析论证了大堤土体采动裂缝的形成条件及其发育深度,得出几点结论:1)目前,淮南淮河大堤在粘土堤土体拉应变超过8～12mm/m、砂土堤超过3～5mm/m时,堤体就会出现裂缝;2)土中裂缝发育深度不会超过与土的力学特性有关的某一极限值。目前淮河大堤粘土堤约为4.0m、砂土堤约为2.0m;3)采取粘土注浆、铺设防渗膜等措施处理后,淮河大堤采动裂缝的存在就不会对河下采煤与大堤安全构成威胁。  相似文献   

Dams and population displacement on China’s Upper Mekong River: Implications for social capital and social–ecological resilience     

《Global Environmental Change》2016

China is home to nearly half of the world’s 50,000 large dams, which provide irrigation, flood protection, and hydroelectricity. Most of these projects involve substantial population displacement, which can disrupt social capital, the webs of interdependence and support that community members maintain with one another through relationships of trust and reciprocity. We use new empirical evidence to examine the association between dam-induced displacement and social capital in China and interpret our findings in the context of social–ecological resilience theory. Our focus is on agricultural households on the Upper Mekong River, where four large hydropower dams have been constructed over the past twenty years.Our broad finding is that resettlement is associated with diminished social capital, as measured by two key indicators: inter-household exchange of financial resources, and inter-household exchange of agricultural labor. These effects differ across the four dam sites in the study based on local economic conditions and changes in resettlement policy. We find that population resettlement is associated with markedly lower levels of agricultural labor exchange. In an economically under-developed setting, this reduces the depth and breadth of social support that agricultural households rely on to produce crops for subsistence and income. This in turn diminishes social–ecological resilience because social capital is a key factor that helps agricultural or resource-dependent communities manage risk and adapt to changes and stressors.We consider the policy implications of our findings in the context of scientific and industry efforts to minimize social harm, promote economic vitality, and improve the sustainability of hydropower as a form of renewable energy.  相似文献   

Hydrological alterations from water infrastructure development in the Mekong floodplains          下载免费PDF全文

Thanh Duc Dang  Thomas A. Cochrane  Mauricio E. Arias  Pham Dang Tri Van  Tonny T. de Vries 《水文研究》2016,30(21):3824-3838

The Mekong floodplains, which encompasses the region from Kratie Township in Central Cambodia to the Vietnamese East Sea, is a region of globally renown agricultural productivity and biodiversity. The construction of 135 dams across the Mekong basin and the development of delta‐based flood prevention systems have caused public concern given possible threats on the stability of agricultural and ecological systems in the floodplains. Mekong dams store water upstream and regulate flow seasonality, while in situ flood prevention systems re‐distribute water retention capacity in the floodplains. The main aim of this paper is to evaluate possible impacts of the recent development of both hydropower dams and flood prevention systems on hydrological regimes in the Mekong floodplains. An analysis of measured daily and hourly water level data for key stations in the Mekong floodplains from Kratie to the river mouth in Vietnam was conducted. Hydropower dam information was obtained from the hydropower database managed by the Mekong River Commission, and the MODIS satellite imagery was used to detect changes in flooding extent related to the operation of flood prevention systems in the Vietnam Mekong Delta. Results indicate that the upper part of the floodplains, the Cambodian floodplains, may buffer upstream dam impacts to the Vietnam Mekong Delta. Flood prevention up to date has had the greatest effect on the natural hydrological regime of the Mekong floodplains, evidenced by a significant increase of water level rise and fall rates in the upper delta and causing water levels in the middle delta to increase. The development of flood prevention systems has also effected spatial distribution of flooding as indicated via a time series analysis of satellite imagery. While this development leads to increase localized agricultural productivity, our historical data analysis indicates that development of one region detrimentally affects other regions within the delta, which could increase the risk of future conflicts among regions, economic sectors and the ecological value of these important floodplains. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

高速铁路浅埋偏压隧道安全进洞方案研究          下载免费PDF全文

贾元霞 《地震工程学报》2022,44(1):22-28

针对傍山浅埋偏压、局部出露地表隧道工程合理施工方案的选取问题,结合现场工程地质及施工环境条件,提出"先在出露地表侧预设钢格栅混凝土护拱,随后反压回填土石,采用暗挖法进洞"的护拱暗挖技术方案,并与放坡明挖、支挡明挖方案进行对比分析.研究结果表明,明挖施工方案虽技术成熟,但用于此类隧道面临着靠山侧高陡边坡开挖及防护工程量大...  相似文献   

Review study on near-natural conditions of Central European mountain streams, with particular reference to debris and beaver dams: Results of the “REG meeting” 2000     

Daniel Hering  Marc Gerhard  Ellen Kiel  Thomas Ehlert  Tanja Pottgiesser   《Limnologica》2001,31(2):81

This paper summarises the results of the “Rhithron Ecology Group” meeting in Essen (March 2000), supplemented by a literature evaluation.An extended view of small mountain streams in Central Europe under “potentially natural conditions” is presented. We focus on the potential impact of natural transverse structures (debris dams and beaver dams) on stream morphology, hydrology, habitat composition and communities. Furthermore, impact of other stream morphological features, which are presently lacking in the Central European landscape, is described.We suggest that Central European mountain streams are characterised by a higher proportion of lentic zones under “potentially natural conditions”. Morphological degradation leads to a loss of lentic zones and to an increase of current velocities and corresponding changes in faunal composition, particularly higher abundance and proportion of rheophilic species and a decrease of species preferring lentic zones. This should be regarded in future stream assessment.  相似文献   

Probabilistic assessment of seismic hazard of dam sites in Jordan     

Azm S. Al-Homoud  Abdallah I. Husein 《Natural Hazards》1995,11(2):123-134

A Probabilistic method is used to evaluate the seismic hazard of nineteen embankment dam sites in Jordan. A line source model developed by McGuire (1978) is used in this study. An updated earthquake catalogue covering the period from 1 A.D. to 1991 A.D. is used for this purpose. This catalogue includes all earthquakes that occurred in Jordan and adjacent areas, more specifically between latitudes 27.0°–35.5° N and longitudes 32.0°–39.0° E.Nine distinct seismic sources of potential seismic activities are identified. The seismic hazard parameters are determined using the method suggested by Kijko and Sellevoll (1989).The Peak Ground Acceleration (PGA) is selected as a measure of ground motion severity. Esteva (1974) attenuation relationship is used in evaluating PGA values at each dam site. Analysis is carried out for 50%, 90%, and 95% probability that is not being exceeded in a life time of 50, 100, and 200 years.Results of analysis indicate that PGA values are higher for dam sites closer to the Dead Sea Fault. This fault is believed to be responsible for most earthquake activities in Jordan and vicinity. The highest PGA value is found to be for Al-Karama dam site.  相似文献   

论岛弧的拱结构   总被引：5，自引：0，他引：5  

何龙清 《地质论评》1994,40(1):1-8

基于海沟－岛弧－弧后盆地体系起伏变化的地壳厚度和岛弧平面上独特的延展方式，从结构力学上看，岛弧实质上是横跨于汇聚板块边界上的二铰拱，弧体及两端支点的地质构造特点都说明了这一点。板块俯冲边界上作用力的方式和方向相当于作用在二铰拱上的竖向均布载荷，因而岛弧选择的合理拱轴为抛物线。为了保持汇聚板块边界的平衡，岛弧呈抛物线形向外扩展，引起弧后盆地向岛弧一侧的扩张，这与大洋中脊的扩张有本质的不同。  相似文献