Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / O amortecimento de ondas de cheias se constitui em uma caracterÃstica fundamental dos reservatÃrios superficiais, uma vez que tem impacto direto na prÃpria seguranÃa da barragem, afetando as outras funÃÃes do aÃude. Logo, se esta caracterÃstica nÃo for suficientemente eficiente para atenuar os picos de vazÃes afluentes, hà o sÃrio risco de ocorrÃncia de âgalgamentoâ; ou seja, a altura da lÃmina dâÃgua vertida supera o valor mÃximo admitido em projeto, levando a um possÃvel rompimento da estrutura da barragem. Muitos reservatÃrios superficiais encontram-se envelhecidos e fora das normas tÃcnicas atuais, sendo preocupante a situaÃÃo no Estado do CearÃ, no qual vÃrias barragens foram construÃdas hà mais de meio sÃculo. Tal fato à especialmente importante, dado que estes reservatÃrios desempenham mÃltiplas funÃÃes. Assim, para garantir que os padrÃes mÃnimos de seguranÃa das barragens brasileiras sejam atendidos, foi aprovada a Lei de Barragens em 2010. Esta lei surgiu como resposta, assim como em muitos paÃses, à ocorrÃncia de expressivos tipos de acidentes em barragens; entre eles, os decorrentes de âgalgamentoâ. Logo, para que o processo de amortecimento de ondas de cheias afluentes aos aÃudes do semiÃrido seja mais detalhado, foram realizadas simulaÃÃes hidrolÃgicas de vÃrios cenÃrios representativos de configuraÃÃes de reservatÃrios e de bacias hidrogrÃficas atravÃs da variaÃÃo dos parÃmetros originais de um reservatÃrio teste (AÃude JoÃo Guerra). Como resultado, determinou-se o impacto de cada parÃmetro fÃsico adimensional e de cada variÃvel no amortecimento. Estes parÃmetros foram agregados em um Ãnico Ãndice, em cuja funÃÃo foi proposto um mÃtodo grÃfico expedito fÃcil para estimar do amortecimento, segundo diversos valores de precipitaÃÃo. O presente estudo revelou ainda que o amortecimento decamilenar, a partir de uma dada fraÃÃo de chuva, pode ser aproximado pelo amortecimento milenar, e o mÃtodo à mais sensÃvel à variaÃÃo do fator de forma do reservatÃrio do que Ãs variaÃÃes das outras variÃveis. / Flood damping constitutes a fundamental characteristic of surface reservoirs, because it has direct impact on the safety of the dam itself, affecting other functions of the dam. So, if this feature is not efficient enough to attenuate the peak inflow, there is a serious risk of occurrence of "overtoppingâ; in other words, the height of the poured water exceeds the maximum value allowed in the project. Many surface reservoirs are getting old and out of the current technical standards, being worrying the situation in the State of CearÃ, in which several dams were built more than half a century ago. This fact is particularly important, given that these reservoirs play multiple roles. Thus, to ensure that brazilians damsâ minimum safety standards are met, The Dams Act was approved in 2010. This law appeared in response, as in many countries, to the occurrence of significant types of accidents, including the ones resulting from âovertoppingâ. Therefore, in order to more detail the process of flood damping in semiarid reservoirs, hydrological simulations were performed for several scenarios that represent settings of reservoirs and watersheds through the variation of the original parameters of a test reservoir (JoÃo Guerra Dam). As a result, it was determined the weight of each dimensionless physical parameter and each variable in the flood damping. These parameters were aggregated into a single index, in whose function it was proposed an easy expeditious graphical method in order to estimate the flood damping, according to different values of precipitation. This study also revealed that the decamillennial damping, from a given fraction of precipitation, can be approximated by the millennial damping, and the method is more sensitive to the variation of the form factor of the reservoir than to the variations of the other variables.

Orientador: Ana Ines Borri Genovez / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-09T19:09:31Z (GMT). No. of bitstreams: 1 Zuffo_MonicaSoaresResio_M.pdf: 4344533 bytes, checksum: 71fc3895338694e910efb1953cf53d6b (MD5) Previous issue date: 2005 / Resumo: As barragens são geralmente obras associadas a um elevado potencial de risco devido à possibilidade de ruptura, com conseqüências catastróficas para as próprias estruturas, para o meio ambiente, com destruição de flora e fauna, e principalmente pelas perdas de vidas humanas e econômicas. Este trabalho tem por objetivo propor e validar uma metodologia alternativa para a avaliação de segurança de barragens. Para a realização deste trabalho escolheu-se algumas barragens localizadas no Ribeirão das Cabras que detém 25% de todas as barragens aprovadas no município de Campinas. A metodologia aqui desenvolvida e denominada de Índice de Segurança de Barragens considerou na sua implementação diferentes critérios que foram avaliados para cada barragem para obter a sua classificação em termos de segurança. A metodologia provou-se válida e uma importante ferramenta na avaliação da segurança de barragens ou açudes. Constatou-se que 37,5% das barragens apresentaram-se em condições insatisfatórias e 62,5% em condições deficientes e, portanto, 100% das barragens necessitam de intervenção urgente. A falta de monitoramento contínuo, a falta de documentação adequada, incluindo-se os projetos, a outorga e a falta de fiscalização das barragens em todas as fases desde o projeto até sua operação são fatores primordiais para a falta de segurança constatada neste estudo. Pode-se alertar que este problema é inerente a muitas barragens, justamente pelo fato de o país ainda não contar com uma legislação específica e não possuir uma articulação clara das responsabilidades de cada órgão competente nas questões que envolvem a segurança de barragens / Abstract: Dams are structures generally associated to high potential risks due to the possibility of their failure, which could bring catastrophic consequences to the structures themselves, to the enrivonment by destructing the flora and fauna and, mainly, because they could cause economical and life losses. The purpose of this work is to propose and validate an alternative methodology to evaluate the security of dams. In order to develop this work some dams located at the Cabras Creek, Campinas, São Paulo, Brazil, were chosen since this river has 25% of all dams approved by the local government of Campinas city. The methodology developed here was called Dam Safety Index (DSI). It considers eighteen different criteria which are applied to evaluate each dam in order to obtain its classification in terms of security. The methodology proved itself to be effective and an important tool to diagnose the safety of dams. As a result, it was found out that 37.5% of the dams were in unsatisfactory conditions and 62.5% were in poor conditions; thus, 100% of dams are in need of urgent repairs not meeting the minimum desired safety level. The lack of a continuous monitoring, lack or imprecise documentation, including their projects and concession files, and no inspection on the part of the authorities in all phases are contributing factors to the lack of security verified in this study. It can be said that these problems are common in many small Brazilian dams, mostly because the country does not have a specific legislation to rule the security of dams and there is no clear responsibility stated as for what each government department should be in charge of / Mestrado / Recursos Hidricos / Mestre em Engenharia Civil

Successful dam design endeavor involves generating technical solutions that can meet intended functional objectives and choosing the best one among the alternative technical solutions. The process of choosing the best among the alternative technical solutions depends on evaluation of design conformance with technical specifications and reliability standards (such as capacity, environmental, safety, social, political etc pecifications). The process also involves evaluation on whether an optimal balance is set between safety and economy. The process of evaluating alternative design solutions requires generating a quantitative expression for lifetime performance and safety. An objective and numerical evaluation of lifetime performance and safety of dams is an essential but complex undertaking. Its domain involves much uncertainty (uncertainty in loads, hazards, strength parameters, boundary conditions, models and dam failure consequences) all of which should be characterized. Arguably uncertainty models and risk analysis provide the most complete characterization of dam performance and safety issues. Risk is a combined measure of the probability and severity of an adverse effect (functional and/or structural failure), and is often estimated by the product of the probability of the adverse event occurring and the expected consequences. Thus, risk analysis requires (1) determination of failure probabilities. (2) probabilistic estimation of consequences. Nonetheless, there is no adequately demonstrated, satisfactorily comprehensive and precise method for explicit treatment and integration of all uncertainties in variables of dam design and risk analysis. Therefore, there is a need for evaluating existing uncertainty models for their applicability, to see knowledge and realization gaps, to drive or adopt new approaches and tools and to adequately demonstrate their practicability by using real life case studies. This is required not only for hopefully improving the performance and safety evaluation process accuracy but also for getting better acceptance of the probabilistic approaches by those who took deterministic design based research and engineering practices as their life time career. These problems have motivated the initiation of this research. In this research the following have been accomplished: (1) Identified various ways of analyzing and representing uncertainty in dam design parameters pertinent to three dominant dam failure causes (sliding, overtopping and seepage), and tested a suite of stochastic models capable of capturing design parameters uncertainty to better facilitate evaluation of failure probabilities; (2) Studied three classical stochastic models: Monte Carlo Simulation Method (MCSM), First Order Second Moment (FOSM) and Second Order Second Moment (SOSM), and applied them for modeling dam performance and for evaluating failure probabilities in line with the above mentioned dominant dam failure causes; (3) Presented an exact new for the purpose analytical method of transforming design parameters distributions to a distribution representing dam performance (Analytical Solution for finding Derived Distributions (ASDD) method). Laid out proves of its basic principles, prepared a generic implementation architecture and demonstrated its applicability for the three failure modes using a real life case study data; (4) Presented a multitude of tailor-made reliability equations and solution procedures that will enable the implementations of the above stochastic and analytical methods for failure probability evaluation; (5) Implemented the stochastic and analytical methods using real life data pertinent to the three failure mechanisms from Tendaho Dam, Ethiopia. Compared the performance of the various stochastic and analytical methods with each other and with the classical deterministic design approach; and (6) Provided solution procedures, implementation architectures, and Mathematica 5.2, Crystal Ball 7 and spreadsheet based tools for doing the above mentioned analysis. The results indicate that: (1) The proposed approaches provide a valid set of procedures, internally consistent logic and produce more realistic solutions. Using the approaches engineers could design dams to meet a quantified level of performance (volume of failure) and could set a balance between safety and economy; (2) The research is assumed to bridge the gap between the available probability theories in one hand and the suffering distribution problems in dam safety evaluation on the other; (3) Out of the suite of stochastic approaches studied the ASDD method out perform the classical methods (MCSM, FOSM and SOSM methods) by its theoretical foundation, accuracy and reproducibility. However, when compared with deterministic approach, each of the stochastic approaches provides valid set of procedures, consistent logic and they gave more realistic solution. Nonetheless, it is good practice to compare results from the proposed probabilistic approaches; (4) The different tailor-made reliability equations and solution approaches followed are proved to work for stochastic safety evaluation of dams; and (5) The research drawn from some important conclusions and lessons, in relation to stochastic safety analysis of dams against the three dominant failure mechanisms, are. The end result of the study should provide dam engineers and decision makers with perspectives, methodologies, techniques and tools that help them better understand dam safety related issues and enable them to conduct quantitative safety analysis and thus make intelligent dam design, upgrading and rehabilitation decisions.

Building a sustainable structure in soil or rock that satisfies all predefined technical requirements implies choosing a rational and effective construction method. An important aspect is how the performance of the structure is verified. For cases when the geotechnical behaviour is hard to predict, the existing design code for geotechnical structures, Eurocode 7, suggests the so-called “observational method” to verify that the performance is acceptable. The basic principle of the method is to accept predefined changes in the design during construction, in order to accommodate the actual ground conditions, if the current design is found unsuitable. Even though this in theory should ensure an effective design solution, formal application of the observational method is rare. It is therefore not clear which prerequisites and circumstances that must be present for the observational method to be applicable and be the more suitable method. This licentiate thesis gives a critical review of the observational method, based on, and therefore limited by, the outcome of the performed case studies. The aim is to identify and highlight the crucial aspects that make the observational method difficult to apply, thereby providing a basis for research towards a more applicable definition of the method. The main topics of discussion are (1) the apparent contradiction between the preference for advanced probabilistic calculation methods to solve complex design problems and sound, qualitative engineering judgement, (2) the limitations of measurement data in assessing the safety of a structure, (3) the fact that currently, no safety margin is required for the completed structure when the observational method is applied, and (4) the rigidity of the current definition of the observational method and the implications of deviations from its principles. Based on the review, it is argued that the observational method can be improved by linking it to a probabilistic framework. To be applicable, the method should be supported by guidelines that explain and exemplify how to make the best use of it. The engineering judgement is however not lost; no matter how elaborate probabilistic methods are used, sound judgement is still needed to define the problem correctly. How to define such a probabilistic framework is an urgent topic for future research, because this also addresses the concerns regarding safety that is raised in the other topics of discussion. / För att i berg eller jord kunna konstruera en anläggning, som uppfyller satta tekniska krav, krävs det att man väljer en rationell och effektiv konstruktionsmetod. En viktig aspekt i detta val är hur man verifierar konstruktionens funktion avseende exempelvis bärförmåga eller stadga. För fall när konstruktionens beteende svårt att förutsäga, erbjuder gällande standard (Eurokod 7) den så kallade observationsmetoden. Denna metod tillåter i förväg förberedda förändringar i designen under konstruktionstiden, om observationer av konstruktionens beteende indikerar att så behövs. På så vis anpassas konstruktionen till de faktiska förhållandena i marken. Trots att detta tillvägagångssätt i teorin borde ge en rationell design, används metoden sällan. Det råder därför oklarheter om vilka förutsättningar och omständigheter som krävs för att observationsmetoden ska kunna användas och dessutom utgöra den bästa lösningen. I denna licentiatuppsats granskas observationsmetoden och dess användbarhet. Målet med licentiatuppsatsen är att belysa de aspekter som kan utgöra svårigheter när observationsmetoden används. Dessa identifierades under arbetet med några fallstudier. Licentiatuppsatsen ger därmed en utgångspunkt för fortsatt forskning för att ta fram en mer användbar definition av observationsmetoden. De viktigaste aspekterna som diskuteras i uppsatsen är (1) den skenbara motsatsen mellan användandet av sannolikhetsbaserade beräkningsmetoder för att lösa komplexa dimensioneringsfrågor och kvalitativa ingenjörsmässiga bedömningar, (2) de begränsningar som finns när man använder mätdata för att utvärdera konstruktioners säkerhet, (3) att det för tillfället saknas krav på säkerhetsmarginal mot brott för konstruktioner som byggts med observationsmetoden, och (4) vad svårigheten att uppfylla Eurokodens strikta definition innebär för metodens användbarhet. Utifrån resultatet av granskningen dras slutsatsen att observationsmetoden kan förbättras genom att ge den ett sannolikhetsbaserat ramverk. För att förenkla användningen bör riktlinjer och anvisningar utformas. Även om metoden utvecklas mot en högre grad av beräkningskomplexitet, kommer ingenjörsmässiga bedömningar också framgent att vara viktiga, eftersom en avgörande aspekt är hur problemställningen formuleras. Med ett sannolikhetsbaserat ramverk ökar möjligheten att lösa de frågeställningar kring säkerhet som också diskuteras i uppsatsen. / <p>QC 20140415</p>

The growing application of risk analysis in dam safety, especially for the owners of large numbers of dams (e.g., U.S. Army Corps of Engineers), has motivated the development of a new tool (DAMRAE) for event tree based dam safety risk analysis. Various theoretical challenges were overcome in formulating the computational framework of DAMRAE and several new computational concepts were introduced. The concepts of Connectivity and Pedigree matrices are proposed to quantify the user-drawn event tree structures with proper accounting of interdependencies among the event tree branches. A generic calculation of Common-Cause Adjustment for the non-mutually exclusive failure modes is implemented along with introducing the new concepts of system response probability and consequence freezing. New output presentation formats such as cumulative risk estimate vs. initiating variable plots to analyze the increase of an incremental (annualized) risk estimate as a function of initiating variable are introduced. An additional consideration is given to the non-breach risk estimates in the risk modeling and new output formats such as non-breach F-N and F-$ charts are included as risk analysis outputs. DAMRAE, a Visual Basic.NET based framework, provides a convenient platform to structure the risk assessment of a dam in its existing state and for alternatives or various stages of implementing a risk reduction plan. The second chapter of the dissertation presents the architectural framework of DAMRAE and describes the underlying theoretical and computational logic employed in the software. An example risk assessment is presented in the third chapter to demonstrate the DAMRAE functionalities. In the fourth chapter, the DAMRAE framework is extended into DAMRAE-U to incorporate uncertainty analysis functionality. Various aspects and requirements reviewed for uncertainty analysis in the context of dam safety risk assessment and theoretical challenges overcome to develop the computational framework for DAMRAE-U are described in this chapter. The capabilities of DAMRAE-U are illustrated in the fifth chapter, which contains an example dam safety risk assessment with uncertainty analysis. The dissertation concludes with a summary of DAMRAE features and recommendations for further work in the sixth chapter.

There are multiple dam failures and dam safety incidents every year in the United States. There are currently no standard policy requirements for when or how to conduct failure or incident investigations. This paper first reviews one of the most significant failures in US history, the failure of Buffalo Creek Dam No. 3 in order to explore the impacts of one significant failure on dam safety policy in the US. The paper then explores the currents state of the industry by reviewing 58 different dam failure or incident investigation reports based on incidents that occurred in the United States from 1960 through 2022. The investigations were analyzed and evaluated for characteristics such as the length of time for the investigation team to get on site, the amount of time to complete the full investigation, what organization funded the investigation, independence of the investigation team, scope of the investigation and several other parameters. This paper makes ten recommendations for improving investigations in the future, including recommended definitions for incidents and failures. The overall purpose was to incorporate all this information to propose legislation that describes the process of performing dam safety incident and failure investigations. The legislation draws from analyses already mentioned and a review of five industry-sponsored safety incident investigation guidelines: (1) the National Transportation Safety Board (NTSB) for investigations of airplane, rail, marine and highway incidents/crashes, in addition to pipeline failures and hazardous material incidents, (2) the National Institute of Standards and Technology (NIST) for building failures, (3) The Nuclear Regulatory Commission (NRC) for the nuclear industry, (4) The Occupational Safety and Health Administration (OSHA) for work safety incidents, and (5) the currently proposed legislation for the National Disaster Safety Board. The proposed dam safety incident and dam failure legislation defines a dam safety incident as an event where a failure mode initiates and progresses but does not lead to an uncontrolled release from the reservoir. It defines dam failure as an event where a failure mode initiates, progresses and leads to an uncontrolled release water from the reservoir. Failures are of three types: low consequence, significant consequence and high consequence. The legislation proposes that all high consequence failures and all failures and incidents that cause evacuations of 500 or more people get federally conducted and funded investigations.

As many dams were built around 1950, the expected life span of these dams are about tobe reached. With this, the need for monitoring and increased understanding of the damsstructural integrity increases. In order to prevent failures, two warning signals are defined;alert and alarm. The main difference being that the first indicates an unexpected changein behavior that needs to be addressed and evaluated in the near future, while the otherrequires that immediate action must be taken to ensure the safety of the dam.This report aims to evaluate the applicability of different models for designing alert values.In order to achieve this goal, two case studies have been performed. The first being onSchlegeis, an arch dam in Austria, and the second Storfinnforsen, a concrete buttress damin Sweden. The methods used are finite element modelling as well as data-based models.Data-based models work on the presumption that the dam behaviour is governed by variationsin environmental conditions such as temperature and water level. The report hasevaluated two commonly used data-based models, hydrostatic thermal time (HTT) and hydrostaticseasonal time (HST), as well as two machine learning based models artificial neuralnetworks (ANN) and boosted regression trees (BRT).The programs used in this report are BRIGADE plus for finite element method and MATLABfor the multi-linear regression analyses HTT and HST, as well as boosted regressiontrees. The neural networks were constructed in Python using TensorFlow and Keras API.The result from the case studies is that the commonly used data-based models HST andHTT perform well enough for creating predictions and alert levels when given a sufficientamount of historical data, approximately 3-5 years. Machine learning such as artificial neuralnetworks while comparable in prediction quality does not further increase the understandingof the dam behaviour and can due to the complexity of designing an appropriate networkstructure be less suited for this type of analysis. Finite element models can also capturethe behavior of the dam rather well. It is however not as accurate as data-based modelswhen sufficient data is available. An FE-model should be used for definition of alert valueswhen insufficient data exists after the dam conditions have been significantly altered, orwhen newly constructed. The main advantage that machine learning provides is that theyperform better for non-linear behavior than multi-linear regression.

There are hundreds of existing dams within the State of Virginia, and even thousands more specifically within the United States. A large portion of these dams do not meet the current safety standard of passing the Probable Maximum Flood. Likewise, many of the dams have reached or surpassed the original design lives, and are in need of rehabilitation. A standard protocol will assist dam owners in completing a dam rehabilitation analysis. The protocol provides the methods to complete the hydrologic, hydraulic, and economic analysis. Additionally, alternative augmentation techniques are discussed including the integration of GIS applications and linear programming optimization techniques. The standard protocol and alternative techniques are applied to a case study. The case study includes a set of flood control dams located in the headwaters of the South River watershed in Augusta County, VA. The downstream impacts of the flood control dams on the city of Waynesboro are demonstrated through the hydrologic and hydraulic analysis. / Master of Science

<p>Hydropower is an important source of energy in Sweden and accounts for about 46 % of the total energy production. Sweden has about 1 200 hydropower plants and with the intention of raising the pressure head of the water and to store water, dams are built by the power plants. The storage reservoirs make it possible to adjust the energy production by demand and season. Dams in connection to the reservoirs are subjected to additional loading during periods of high floods or when an icecap in the winter is formed on the reservoirs. In order to maintain the dam safety, the power companies in Sweden are working with guidelines for dam safety from RIDAS. An important part of the work of dam safety is FDU that is carried out with purposes of improving the work of dam safety. A FDU made for the Skålan dam in the River of Ljungan showed that the levels of the safety factors for sliding and overturning of the dam was not fulfilled when subjected to loads from an icecap. The object of this thesis was to follow up the FDU and by carrying out extensive stability calculations on all parts of the Skålan dam, investigate what safety factors the different parts will get and also investigate some proposal measures in order to increase the dam stability.</p><p>The stability calculations for the dam have been performed according to directions in RIDAS at four loading cases. Loading case I and II means a water level to the retained water level and an ice load of 200 and 100 kN/m respectively. Loading case III and IV means a situation without ice load but with a water level to the retained water level respectively a water level to a meter above the retained water level. The stability of the dam was studied with regards to sliding and overturning. The results from the stability calculations showed for both loading case I and II that the majority of the parts of the Skålan dam did not fulfill the levels of the safety factors. The calculations also showed that some parts of the dam did not fulfill the stability criteria of sliding at loading case III, which implies that these parts of the dam actually have not enough weight.</p><p>The measure proposals studied were the ice preventive measures IR-elements and circulation of the deep warm water and the stability increasing measure with pre strained rock anchorages. The net present value (NVP) for the different measures were calculated with a life length of the dam estimated to 60 years. The results from the calculations of the NVP showed that the most economically feasible measure is circulation of the water but when considering the results from the stability calculations, the most suitable measure is the rock anchorages. Therefore, a combination of rock anchorages on parts which not fulfills the stability criteria in combination with circulation of the water is suggested to be the best measure.</p> / <p>Vattenkraften är en viktig energikälla i Sverige som utgör ca 46 % av den totala energiproduktionen. I Sverige finns det ca 1 200 kraftverk och i syfte att öka fallhöjden och lagra vatten bygger man dammar i anslutning till kraftverken. Dammarna skapar stora magasin med vatten och gör det möjligt att anpassa elproduktionen efter säsong och behov.</p><p>Dammar och kraftverk vid vattenmagasinen utsätts för extra belastning under perioder med höga flöden samt vid islaster och för att upprätthålla dammsäkerheten har man tagit fram RIDAS - kraftföretagens riktlinjer för dammsäkerhet. Inom ramen för dammsäkerhetsarbete utförs fördjupade dammsäkerhetsutvärderingar, FDU, för att arbeta förebyggande och hitta möjligheter till förbättring av dammsäkerhetsarbetet. I en FDU gjord för Skålandammen i Ljungan påvisades att de av RIDAS uppsatta säkerhetsfaktorerna för glidning och stjälpning inte uppfylldes vid islast. Syftet med detta arbete var att följa upp FDU:n och med utförliga stabilitetsberäkningar på Skålandammens alla delar (monoliter) undersöka hur dessa klarar säkerhetsfaktorerna vid olika lastfall, hur stort problemet med islast är samt ta fram åtgärdsförslag för att öka dammens stabilitet.</p><p>Beräkningarna har utförts enligt RIDAS anvisningar för stabilitetsberäkningar vid fyra olika lastfall där de två första innebär en vattennivå till magasinets dämningsgräns samt en islast på 200 respektive 100 kN/m och de två andra behandlar en situation utan islast men med en vattennivå till dämningsgränsen respektive en vattennivå till 1 meter över dämningsgränsen. Stabiliteten kontrollerades med avseende på stjälpning och glidning.</p><p>Resultatet av stabilitetsberäkningarna visade att för majoriteten av Skålandammens monoliter uppfylls inte stabilitetskraven vid en islast på vare sig 200 eller 100 kN/m. Det visades även att ett fåtal monoliter inte uppfyller säkerhetskraven för glidning vid lastfallet utan islast med en vattennivå till dämningsgränsen, vilket indikerar på att dessa monoliter är för lätta.</p><p>De isfrihållande åtgärdsförslagen som jämfördes var IR-element och cirkulering av vattnet med hjälp av luftbubblor och den stabilitetshöjande åtgärden med förspända bergförankringar. Nuvärdet för dessa åtgärder beräknades sedan med antagandet att dammen har en livslängd på 60 år. Resultatet från nuvärdesberäkningen visade att det billigaste alternativet är cirkulering av vattnet men utifrån stabilitetsberäkningarna är det mest fördelaktigt att använda den stabilitetshöjande åtgärden med bergförankringar. Med anledning av detta föreslås ett alternativ med bergförankringar på de monoliter som inte uppfyllde säkerhetskraven vid lastfall utan is i kombination med cirkulering av vattnet som den mest lämpliga åtgärden.</p>

Constructing sustainable structures in rock that satisfy all predefined technical specifications requires rational and effective construction methods. When the geotechnical behaviour is hard to predict, the Euro­pean design code, Eurocode 7, suggests application of the observational method to verify that the performance is acceptable. The basic principle of the method is to accept predefined changes in the design during con­struction to comply with the actual ground conditions, if the current de­sign is found unsuitable. Even though this in theory should ensure an effective design solution, formal application of the observational method is rare. Investigating the applicability of the observational method in rock en­gineering, the aim of this thesis is to identify, highlight, and solve the aspects of the method that limit its wider application. Furthermore, the thesis aims to improve the conceptual understanding of how design deci­sions should be made when large uncertainties are present. The main research contribution is a probabilistic framework for the observational method. The suggested methodology allows comparison of the merits of the observational method with that of conventional design. Among other things, the thesis also discusses (1) the apparent contradiction between the preference for advanced probabilistic calculation methods and sound, qualitative engineering judgement, (2) how the establishment of limit states and alarm limits must be carefully considered to ensure structural safety, and (3) the applicability of the Eurocode defini­tion of the observational method and the implications of deviations from its principles. / För att kunna konstruera en anläggning i berg, som uppfyller satta tek­niska krav, krävs det en rationell och effektiv konstruktionsmetod. När konstruktionens beteende är svårt att förutsäga, erbjuder den europeiska standarden Eurokod 7 den så kallade observationsmetoden. Denna metod tillåter i förväg förberedda förändringar i designen under konstruktions­tiden, om observationer av konstruktionens beteende indikerar att så behövs. På så vis anpassas konstruktionen till de faktiska förhållandena i marken. Trots att detta tillvägagångssätt i teorin ger en rationell design, används metoden sällan i enlighet med Eurokod 7. Denna doktorsavhandling undersöker tillämpbarheten av observa-tionsmetoden när man bygger i och på berg. Målet är att belysa de aspekter som begränsar dess användning och i dessa fall föreslå förbätt­ringar som ökar tillämpbarheten. I ett vidare perspektiv syftar avhand­lingen även till att förbättra den konceptuella förståelsen för hur beslut bör fattas i designprocessen när det finns stora osäkerheter. Avhandlingen visar hur observationsmetoden kan användas i ett san­nolikhetsbaserat ramverk. Metodiken ger användaren möjlighet att jäm­föra för- och nackdelarna med observationsmetoden och konventionell dimensionering. Avhandlingen diskuterar bland annat även (1) den skenbara motsatsen mellan användandet av sannolikhetsbaserade beräkningsmetoder för att lösa komplexa dimensioneringsfrågor och kvalitativa ingenjörsmässiga bedömningar, (2) hur larmgränser och brottgränstillstånd bör definieras för att ge tillräcklig säkerhetsmarginal, samt (3) hur Eurokod 7:s strikta definition av observationsmetoden påverkar dess användbarhet. / <p>QC 20160926</p>