Orientadores: Tiago Zenker Gireli, Paulo Vatavuk / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-27T09:39:25Z (GMT). No. of bitstreams: 1 Morais_VitorHugoPereirade_M.pdf: 5887313 bytes, checksum: d9a8b6193d7d493225eafddb46579af3 (MD5) Previous issue date: 2015 / Resumo: A busca pelo entendimento do comportamento dos fluidos é realizada geralmente por meio de métodos experimentais. Por exemplo, são clássicas as soluções utilizando-se modelos físicos reduzidos na otimização de projetos de grandes estruturas hidráulicas, como as barragens. A utilização de métodos experimentais é onerosa e demanda um tempo relativamente alto. Este fato, associado ao desenvolvimento tecnológico de computadores digitais de alta capacidade de processamento, fez surgir alternativamente às soluções clássicas, modelos computacionais que resolvem as equações que descrevem o comportamento dos fluidos com condições de contorno gerais e geometrias complexas. Neste sentido, este trabalho tratará de uma avaliação comparativa dos resultados obtidos em uma simulação do escoamento por um extravasor de uma barragem utilizando o programa FLOW-3D®, com os obtidos em um modelo físico reduzido presente na Fundação Centro Tecnológico de Hidráulica (FCTH) da Universidade de São Paulo / Abstract: Usually the research on the the behavior of fluids is developed using experimental methods. For instance, it is usual to apply physical scale models models in the optimization studies of hydraulic structures design, such as dams. Using experimental methods is expensive and demands a relatively high time of tests. This fact, associated with the technological development of digital computers of high processing capacity, has given rise, alternatively to the classical solutions, computational models that solve the equations that describe the behavior of fluids with general boundary conditions and complex geometries. In this way, this report will present a comparative evaluation of the results obtained in a simulation of a flow through a dam spillway using a mathematical model called FLOW-3D® with those obtained in a physical scale model operated by the Fundação Centro Tecnológico de Hidráulica (FCTH) of the University of São Paulo / Mestrado / Recursos Hidricos, Energeticos e Ambientais / Mestre em Engenharia Civil

O estudo pretende subsidiar o processo de tomada de decisão na concepção e planejamento de infraestruturas de apoio a grandes empreendimentos por parte dos empreendedores, dentro de uma política que considere as possibilidades de promover o desenvolvimento regional a partir deste marco, representado pela introdução maciça de investimentos. O trabalho enfoca principalmente o caso de usinas hidrelétricas, fazendo um paralelo com infraestruturas de apoio a minerações. Pretende-se tornar mais claras as consequencias da política adotada pelo setor no planejamento e implantação de vilas residenciais e alojamentos sobre o meio socioeconomico no qual se inserem. / The study aims to contribute to the decision making process on the conception and planning of support infrastructures of large projects, adopting a policy that considers the possibilities of promoting regional development induced by the massive introduction of investiments. The main focus is on hydroelectric power plants compared to mining projects. It is aimed to clarify the consequences of each different policy on the socioeconomic environment.

The thesis is focused on the issue of black swans in the water structure. More detail risks and hazard dam. History has shown us that sophisticatedly structure as dam is not perfect. Failure can cause weather, natural disaster, bad chance or deliberate attack. A detailed analysis of the current situation, I mapped historic dam failure, which can cause black swan. In thesis is a reseach on knowledge of the population in this issue. Based on the analysis and obteined information was proposed measures to improve the situation.

Problems with erosion in unlined spillways of dams, have caused environmental and safety hazards, and necessitate the development of reliable scientific methods to assess the erodibility of the bedrock material. In an attempt to analyze the causes and effects of different geological, geotechnical, hydraulic, hydrological and engineering design parameters on erosion of unlined spillways, a number of dam spillways in the R.S.A. were studied. All the parameters considered important for the erosion resistance of the rock were collected and correlated with hydraulic factors and observed extent of erosion. Rock type, strength, weathering and uniformity of the geological conditions are important geotechnical considerations while velocity and energy of the water flow are the main hydraulic parameters. The main consideration of the study was the effect of the discontinuities. All the properties of the jointing of the rock mass, such as number of joint sets, RQD, joint spacing, joint separation, joint orientation, roughness and filling material, were surveyed. Joints. weaken the rock mass and induce removal of the rock blocks if the joint properties are unfavourable to stability. The jointed bedrock is much less resistant to flowing or falling water, the result being an extensive and quickly formed scour. Various rock mass classification systems have been applied and a reasonable correlation between rock class and extent of erosion was established by means of slightly modified Kirsten (1982) and Weaver (1975) rippability classifications. A number of methods for the prevention and repair of erosion damage have been proposed. / Dissertation (MSc)--University of Pretoria, 1990. / gm2014 / Geology / unrestricted

The Lossen dam is an embankment dam in the Swedish river Ljusnan. The dam is founded on thick layers of stratified glaciofluvial sediments and till. Ever since construction, there have been problems with high pore pressures, large seepage flows and springs downstream of the right part of the dam. After the first filling of the reservoir, a large drainage trench was constructed downstream of the dam to lower pore pressures. Sinkholes and settlements downstream of the dam have occurred repeatedly over the lifetime of the dam, particularly in the area surrounding the large drainage trench. This study aims to investigate the causes of the sinkholes and assess the risks of internal erosion in the foundation and in the soil downstream of the dam. A model of the groundwater flow has been created in Visual MODFLOW. Calculations for assessing the soils susceptibility for contact erosion and suffusion have been performed, using soil gradation curves (both from the 1960s and from new samples). The results from the erosion calculations show that the probability of contact erosion being the sole cause of the internal erosion is minor. However, a majority of the soil samples tested are internally unstable (susceptible for suffusion). The possibility of backward erosion piping can not be dismissed but would need further investigation in order to be properly assessed. Due to the very heterogeneous structure of the soil in the area downstream of the dam, it is hard to predict the extent of the eroding soil layers and, thus, the future development of the erosion. A conclusion is that the soil downstream of the dam is subject to internal erosion, which is also the cause of the observed sinkholes and settlements. The internal erosion is probably not a threat to dam safety at the moment, but can possibly evolve as a problem in the future. Therefore close monitoring of the changes in seepage patterns and sediment transport is recommended. Possible solutions to stop the erosion include extending the drainage system with more pressure relief wells, and placing a filter blanket in the seepage exit area. / Lossendammen är en jorddamm i älven Ljusnan.  Dammen är byggd ovanpå tjocka lager av morän och isälvssediment. Sedan första dämningen 1962 har problem med höga portryck, stora läckageflöden och källsprång nedströms dammen uppkommit. Efter första dämningen grävdes ett stort dränagedike (kallat Slits 19) ut nedströms om dammen, för att sänka portrycken i området. Sjunkhål och sättningar har uppkommit återkommande under dammens livstid, speciellt i området kring slitsen. Målet med denna studie är att undersöka orsaken till de uppkomna sjunkhålen och sättningarna, samt att bedöma risken för fortsatt intern erosion i dammens undergrund och i jorden nedströms dammen. En modell över grundvattenflödet i området har skapats i Visual MODFLOW. Jordens fallenhet för kontakterosion och suffusion har beräknats med hjälp av kornfördelningskurvor från jordprover (majoriteten av vilka är från 60-talet, samt några nya). Resultaten från beräkningarna visar att risken för att kontakterosion initieras är liten. Däremot visar en majoritet av de testade kornfördelningskurvorna att jorden är internt instabil (har fallenhet för suffusion). Sannolikheten för att bakåtskridande erosion initieras kan inte uteslutas baserat på det underlag som förelegat, men en pålitlig bedömning skulle kräva ytterligare undersökningar. Eftersom jorden under och nedströms dammen är väldigt heterogen, och de olika lagrens storlek och utbredning är okänd, är det svårt att förutspå hur erosionen kommer att utvecklas i framtiden. Slutsatsen är att jorden nedströms dammen utsätts för fortlöpande inre erosion. Inre erosion är också orsaken till de uppkomna sjunkhålen och sättningarna. I nuläget är erosionen ingen risk för dammsäkerheten, men kan komma att bli det i framtiden. Noggrann övervakning av eventuella förändringar i läckagemönstren och sedimenttransport är viktig. Bland möjliga lösningar för att avstanna erosionen finns utökning av dränagesystemet med nya filterbrunnar, samt att lägga ett filtrerande skyddslager över området där källsprången sker.

Majoriteten av de svenska betongdammarna uppfördes under 1900-talet och börjar därför närma sig sin uppskattade livslängd; 50-160 år. Några av dessa betongdammar används för att utvinna vattenkraft. Vattenkraft är Sveriges största energikälla och utgör ca 45% av vår totala elproduktion. Det ställs därför krav på att reparera samtliga betongdammar inför fortsatt förvaltning och för att bibehålla vår elproduktion. Betongdammar sammanlänkas med hjälp av dilatationsfogar. Dilatationsfogar hjälper betongkonstruktionen att stå emot de rörelser som sker under temperaturvariationer. På grund av dilatationsfogens placering i konstruktionen så är det väldigt svårt att genomföra och säkerställa en reparation. Inuti dilatationsfogens plåtfogbandskanal, i fallen där dilatationsfogen besitter två fogband, används bitumen som ett vattenstopp. Varje dilatationsfog som tätas med bitumen genererar en klimatpåverkan om ca 0,5 till 1,5 kg CO2-e per fog. Om fogbanden, inom dilatationsfogen, eller betongen i närheten av dessa skadas så kan därav bitumen lackas ut och följa med vattnet nedströms. Om detta sker så genereras en ökad miljö- och klimatpåverkan. Då nytt material måste produceras för att avlasta bitumenförlusten, fogbanden måste reparareras och bituminet släpps ut i naturen. Därför är det även av intresse att minimera eller helt ta bort det nuvarande vattenstoppet av bitumen.   I ett försök att minimera komplexiteten och trappa ned på bitumenanvändningen undersöks i detta examensarbete en reparation med hjälp av bentonitpellets. Reparationen sker via ett borrhål som sedan återfylls med bentonitpellets. Det finns två betongdammar i Sverige som använt sig utav denna metodik. Examensarbetet syftar således till att utvärdera hur denna reparationsmetodik står sig, dels längre fram i tiden, mot andra alternativ och framtida förväntningar om att eventuellt kunna ersätta bituminet mot andra material. Inledningsvis undersöktes bentonitpelletsens svällförmåga samt hur materialet ansamlar sig fukt. Detta genom nya framtagna metoder, som delvis, är baserade på tidigare standarder. Med hjälp utav dessa nya metoder kunde materialegenskaper också utvärderas mer långsiktigt. För att utvärdera långtidsperspektiv tilläts bentonitpelletsen att genomgå frostcykler i ett temperaturväxlingsskåp. Där fem dygn i temperaturväxlingsskåpet, uppskattningsvis, motsvarar de svenska klimatförhållanden i norra Sverige som förväntas inträffa under ett år. Bentonitpelletsen utvärderades sedan via samma testmetodik efter 1,5 och 3 år. Resultatet från bentonitpelletsens fuktupptagningsförmåga visade på en skillnad mellan de olika sorterna. Den rena Na-bentonitens fuktupptagningsförmåga står sig bättre med tiden, jämfört mot de kemiskt framställda Na-bentonitpelletserna. Resultaten från svällförmågan tyder dock på att samtliga bentonitpellets upplever en försämring allt eftersom. Om vattenkvoten är låg innan frostcykler så ökar bentonitpelletsens svällförmåga, på grund av att den uttorkas. Efter den första experimentella delen, och insamlade materialkunskaper från denna, uppfördes en miniatyrversion av en verklig dilatationsfog. Bakgrunden till detta genomförande var att man ville undersöka hur stort tryck som bentonitpelletsen klarar av att hålla tillbaka innan materialet går till brott. Vattenfalls konstruktörer uppförde testriggen och denna bestod främst utav plåt. En delad betongkub, med ett hål i mitten, placerades i konstruktionen. Hålet fylldes därefter upp av bentonitpellets. För att kunna åskåda hur materialet betedde sig under tryckförsök bekläddes konstruktionens ovandel med plexiglas. På denna plexiglasskiva installerades en manometer. Med hjälp av manometern, och ett konstant inflöde av vatten, kunde trycket i testriggen uppmätas och regleras. När den sedimenterade bentonitpelletsen går till brott så sjunker trycket på manometern. Resultatet från tryckförsöken visar på ett samband mellan bentonitpelletsens deklarerade svälltryck och det tillförda vattentrycket. Beroende på inflödet kan en reparation med bentonitpellets maximalt klara av att hålla tillbaka ett tryck motsvarande 5 till 12 höjdmeter av vatten – där det exakta värdet baseras på tiden den tillåtits att sedimentera. Dessa värden gäller för dess initiala förmåga. Hur materialet står emot vattentryck längre fram i tiden behöver fortsatt utvärdering. Baserat på studiens resultat så kommer inte den tidigare genomförda reparationen, i en av betongdammarna, att hålla – eftersom denna reparation överstiger 12 höjdmeter. Baserat på informationen som presenterats i denna rapport råder det en fortsatt osäkerhet om bentonit kan användas i betongkonstruktioner. Området kräver således fortsatt forskning för att säkerställa dess långsiktiga hållbarhet inom betongkonstruktionen. / Most of Sweden’s concrete dams were built during the 1900’s. Therefore, they are starting to reach the estimated end of their life-cycle; 50-160 years. Some of these concrete dams are used for hydroelectric purposes. Hydroelectric power is one of Sweden’s primary source for electricity, which approximately makes for 45% of our total electric production. Hence, the need for reparation is increasing for further management and maintaining our electricity production in these concrete dams. Concrete dams are linked by expansion joints. These expansion joints help to reduce the stress, during swelling and shrinking, in the concrete caused by temperature variation. Due to the placement of these expansions joint, they become difficult to repair as well as ensuring the success of a reparation. Inside the expansion joint there are dimbands. The dimbands can be sealed with bitumen to help their water stopping abilities. For every expansion joint that is sealed with bitumen the estimated climate impact is 0,5 to 1,5 kg CO2-e per joint. If the dimbands, inside the expansion joint, or the surrounding concrete gets damaged or breaks the bitumen varnishes downstream. This generates for an increased environmental and climate impact, due to the need for new bitumen and steel to fill and seal the leak and oils being released into the surroundings. Therefore, it is also of interest to reduce the usage of bitumen or remove it completely from these dimbands. To minimize the complexity and reduce the usage of bitumen this thesis will evaluate a reparation method with bentonite pellets. The reparation method consists of a borehole, which is then backfilled, with bentonite pellets. There are two concrete dams in Sweden which have used this method. Therefore, this thesis work also aims to evaluate how this reparation will last, regarding time, against other options and future expectations regarding the replacement of bitumen. To begin, the bentonite pellets where first evaluated based on their swelling capabilities and moisture absorption. These attributes were tested by new methods, which are partly based on previous standards. These new methods for the material properties also allowed for long-term evaluation. To evaluate how the bentonite pellets would react over time they were placed in a temperature change cabinet. Five days in these cabinets, were assumed to, correspond to the Northern Swedish climate changes that takes place over a year.  The bentonite pellets were then evaluated by the new methods after 1,5 and 3 years. The results, for both swelling and moisture absorption, showed a difference depending on the bentonite type. The pure Na-bentonite moisture absorption has better absorption capabilities over time, compared to chemically produced Na-bentonite. The results from swelling shows that, regardless of bentonite type, they all induce worse swelling capabilities over time. Although, if they begin thawing cycles at a lower water content their swelling capabilities increases due to the bentonite experiencing exsiccation.  After the first experimental part, and this newly gathered material knowledge, a miniature version of a concrete dams’ expansion joint were built. The background to this was to research how many altitude meters (mVp) the bentonite pellets could withstand before collapse. Vattenfalls engineers built the testrigg, expansion joint, which primarily consisted of steel. A splintered concrete cube, with a predrilled hole in the middle, was then placed in this steel cartridge. The hole was then filled with bentonite pellets. To see the sequence of the material reaction during pressure tests the testrigg had a top of plexiglass. A manometer was then attached to the plexiglass. The manometer, and a consistent flow of water, allowed for the pressure to be monitored and regulated. When the sedimented bentonite pellets collapses the pressure drops.  Results from the pressure tests show a correlation between the bentonite pellets declared swelling pressure and the externally supplied water pressure. Depending on the inflow the bentonite pellets can withstand a pressure between 5 to 12 meters of water height – where the exact value is given by the time it is allowed to sediment. These values only consider the initial expansion of the material. Further research is required to evaluate how much water pressure the material can withstand over time. Based on the findings of this study one of the previously repaired concrete dams’ bentonite seal will collapse in due time, since the reparation exceeds 12 meters in height. Based on the information provided in this thesis it is difficult to decide whether a bentonite seal will be beneficial for the concrete structure. Further research is required to ensure the sustainability of using bentonite inside concrete structures.

Safety of dams can be evaluated based on the risk analysis methodologies that accounts for estimation of the risks associated to the dam-reservoir system. For this purpose it is important to estimate the probability of load events and probability of failure for several failure modes. The following thesis emphasises on estimation of the probability of one specific failure mode, i.e. “sliding failure” for a concrete gravity dam. The main idea behind this thesis was to analyse the estimation of the probability of sliding failure of an existing dam by obtaining the relationships among the different load events, factors of safety associated to those events and the probability of failure estimated using numerical simulation techniques together with different reliability methods. The analysed dam is taken from theme C of the eleventh ICOLD Benchmark workshop on numerical analysis of dams. The thesis covers the methodology for estimating the probability of failure of a given concrete gravity dam with five water levels, considering the sliding failure mode along the dam-foundation interface along with the estimation of factors of safety for each water level and with two different drainage conditions. First order second moment Taylor’s Series Approximation is being used as Level 2 reliability method and Monte Carlo simulation as Level 3 reliability method to estimate the probability of failure against sliding of the dam. Conclusions are drawn in the end by comparing the results obtained from factor of safety estimation and probability of failure for each water level and drainage condition, followed by suggestions for further research in the context of sliding stability of concrete dams.

Over the last century, the construction and management of large dams and stream-flow diversions, and periodic drought have resulted in significant declines in stream flow of the lower Rio Grande in the Big Bend region. Reductions in mean annual flow and peak discharge have resulted in channel narrowing by the formation of vertically accreting inset floodplains. Narrowing has been temporarily interrupted by infrequent large dam releases greater than 1000 m3/s that have temporarily widened the channel; however, after each of these events, narrowing has resumed. Prior to 1942, floods of this magnitude occurred approximately once every 4 years and maintained a wide sandy channel. Since 1942, they have occurred 4 times. The decline in frequency of these large floods has resulted in a channel approximately 50% narrower than in the 1940s. Since the most recent channel widening floods in 1991, the channel has narrowed between 35 and 50%. In two large floodplain trenches, we observed between 2.75 and 3.5 m of vertical accretion during the same period. Additionally, nearly 90% of bare active channel bars have been converted to vegetated floodplains. Since 1991, the cross section channel area at the Johnson Ranch gage has decreased by approximately 30%. The reduction in cross section area and the invasion of non-native vegetation have resulted in higher flood stages, flooding at lower discharges, and continued vertical accretion. Channel narrowing has negatively impacted the native and endemic aquatic ecosystem through the loss of ecologically important habitats such as backwaters, side channels, and low velocity portions of the channel. Reductions in cross section area and resultant increased flood stages have also endangered historic cultural sites within the Big Bend region. Restoration efforts are currently underway within the region without a clear understanding of these historical channel changes and why they occurred. Our reconstruction of historical channel changes shows that the most significant periods of channel narrowing occurred during drought and increased stream-flow management. Management practices also appear to have enabled the invasion of non-native riparian species, which promoted sedimentation, bank stabilization, and additional channel narrowing. In order to restore historical measures of channel width, management options include non-native vegetation removal, common low magnitude dam releases that provide flood disturbance and prevent vegetation establishment, and large dam releases in excess of 1000 m3/s that create and maintain a wide channel. Vegetation management is expensive; and time consuming, and managed dam releases are politically unpopular and expensive, however, without the management of non-native riparian species and reinstatement of portions of the historical flood regime, ecological restoration will be difficult.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 60-61. / by Gregory Paul Matthews. / M.S.

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