Thesis (Ph.D.) -- McMaster University, 1997. / Includes bibliographical references (leaves 241-248). Also available via World Wide Web.

Thesis (Ph.D.) -- McMaster University, 1997. / Includes bibliographical references (leaves 179-194). Also available via World Wide Web.

Thesis (Ph. D.)--Carleton University, 1992. / Also available in electronic format on the Internet.

In the classical design method for gravity dams, the designs are conducted in the linear elastic isotropic material domain. For many decades the so-called ‘classical method’ (or conventional method) was used to design gravity dams. This method is based on the Bernoulli shallow beam theory. Despite much criticism expressed by academics regarding the basis of the theory, dam design engineers are still using the classical method to design gravity dams. Currently, in most dam building countries the various codes of practice are standardised and based on this method, and engineers have confidence in these codes. This state of affairs will probably continue until structural engineers come up with a viable alternative for designing gravity dams more precisely. The perception of increased risk is always a critical aspect to overcome when introducing an alternative design method, especially when the established, well-known methodology has proved to be safe. However, when so-called ‘back analyses’ are performed on existing dams, it is not so straightforward to assess the safety margin of these structures. Material properties and their yielding or failure characteristics are now becoming important in evaluating these structures accurately in the non-linear domain. With the growing popularity of roller compacted concrete as a dam building material, the attractiveness of gravity dams has also increased and the author is of the opinion that the finite element method could be utilised more efficiently to optimise gravity dams. But, as with any new or alternative design method, the parameters and means of evaluation should be developed to establish a workable and reliable technique. The objective of this dissertation is to develop a practical methodology for the non-linear analysis of gravity dams by means of the non-linear finite element method. A further aspect of this dissertation is the inclusion of a broad guideline on the application of the latest dam design standards used in South Africa for both the classical and finite element methods. In order to gain a better understanding of the basic design criteria, a literature survey was conducted on the evolution of dams and the various theories developed in the past to design and optimise gravity dams. The literature survey included the examination of gravity dam safety criteria and some available statistics on dam failures. The International Committee on Large Dams (ICOLD) has interesting statistics on dam failures and their causes. A few typical dam failures are presented to illustrate what can go wrong. During this literature research, a thorough study was done on the non-linear material theory, with special reference to the Mohr-Coulomb and Drucker Prager material models. The findings of the study are used to illustrate how the non-linear material models are incorporated into the finite element method and in what manner the different material parameters have an influence on the accuracy of the results. As already mentioned, currently the classical method is still a recognised design standard and for this reason a summary is presented of the South African Department of Water Affairs and Forestry’s practice for designing gravity dams. This includes the latest concepts on load combinations and factors of safety for these load conditions. This summary of current practice is used as a stepping stone for the proposed load combinations that could be used for the finite element method as these are not always compatible. However, this dissertation does not deal with the full spectrum of load combinations and the scope is limited to hydrostatic loads. Although the finite element method is a very powerful structural engineering tool, it has some serious potential deficiencies when used for dam design. The most serious problem concerns the singularities and mesh density, which develop high stress peaks at the heel of the dam wall. This problem is illustrated and some practical finite element examples are given. Some solutions for addressing this problem are also presented. It is concluded that an effective method for overcoming the singularity problem is to use the non-linear material yielding model. In order to calibrate the non-linear Drucker Prager model, several finite element benchmarks were conducted, based on work done by other researchers in the fracture mechanics field. Although the theory of the Drucker Prager model is not based on fracture mechanics principles, this model simulates the failure of the concrete material very well. To demonstrate this, various benchmarks were conducted, such as a pure tension specimen, a beam in pure bending, a beam combined with bending and shear, the flow models of Chen (1982), a model of a gravity dam and, finally, a full-size gravity dam. The next step in the study was to calibrate the Drucker Prager model with the concrete material properties used in existing dams of different construction methods and ages. The material strength of the concrete was statistically analysed and the average strength was calculated. The important ratio of tensile strength to compression strength (ƒt/ƒc) was also examined and the findings are presented. This ratio is important to get accurate results from the Drucker Prager model. The normal input parameters for the Drucker Prager model are the internal friction angle of the material (φ) and the cohesion (c). Scrutiny of the work done by Chen (1982) helped to find a useful solution to obtaining the parameters for the non-linear finite element method without determining the ö and c values, but by using the material tensile and compression strengths instead. The formulation is demonstrated in the chapter on theory. To illustrate the usefulness of the non-linear yielding model a few case studies were conducted. A hypothetical triangular gravity dam structure was analysed because it was widely used in other literature studies and a useful comparison could be made. Then, a case study of an 80-year-old concrete gravity dam was performed. The uniqueness of this dam lies in the fact that it was designed before the theory of underdrainage was used in South Africa and the dam has a characteristic shape due to its relatively steep downstream slopes compared with today’s standards. A study of material strength sensitivity was also done on this dam to evaluate its stability under severe load conditions. The last case study presented is on a recently designed 75-m-high roller compacted concrete gravity dam, optimised primarily by the classical method. The non-linear Drucker Prager yield model was used to evaluate this structure, with the actual material strengths taken from the laboratory design mix results. Although the finite element method was used during the design stage of this dam, it was used mainly to check the results of the classical method. The finite element method was also used to do studies on this dam where the classical method could not be used, such as studies of temperature and earthquake load conditions (not included in this research). The factor of safety against sliding was also determined using the results obtained from the finite element method and compared with the results obtained from the classical method. This case study gives an approximate comparison between the classical method and the finite element method. Finally, a methodology is proposed for analysing a gravity dam. Procedural steps are given to describe the methodology. With regard to the future, the advantage of the non-linear finite element method is that it can easily be extended to contemporary 3-D analysis, still using the same concept. Many dams can only be accurately evaluated by a full 3-D analysis. There is a modern tendency to design gravity dams in 3-D as well so as to evaluate their stability against sliding in the longitudinal direction. The non-linear 3-D finite element method is also used for arch dams, for which very few alternative numerical analysis methods are available. Moreover, the non-linear finite element method can be extended to earth and rock-fill embankments. / Dissertation (MEng)--University of Pretoria, 2009. / Civil Engineering / unrestricted

Thesis (M. Eng.(Structural Engineering))--University of Pretoria, 2008. / Includes bibliographical references.

Thesis (PhD(Engineering)(Civil Engineering)) --University of Pretoria, 2007. / Includes bibliographical references.

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.

The safety of a concrete dam is ensured by designing according to failure criteria, for all combinations of loads using safety factors. Today in Sweden, RIDAS, the Swedish power companies’ guidelines for dam safety, is used for the design of dams and is based on BKR, the National Board of Housing, Building and Planning. Swedish dams are designed to resist two global failure modes; sliding and overturning. Combination of failure modes, that should be considered in the design of concrete dams, is however fairly unknown. Since 2009 the Eurocodes was adopted and came into force 2011. The Eurocodes have replaced BKR in the design of most structures in Sweden where the partial factor method is used to ensure safety in the design. The objective of this report was to examine if the design criteria for concrete dams in today’s condition are enough to describe real failure modes. The other objective was to analyse if Eurocode is comparable to RIDAS in dam design. The stated questions were answered by performing a literature study of known dam failures and analytical calculations for different types of concrete gravity dams, with varying geometry and loading conditions. The programs CADAM and BRIGADE were also used as calculation tools to further analyse if failure occurred as expected. The results from the analytical calculations together with the performed FE analysis indicate that limit turning does occur and often generate lower safety factors compared to overturning. Limit turning is similar to overturning failure although it accounts for material failure in the rock. This design criterion is therefore, highly dependent on the quality of the rock and requires investigations of the foundation to be a good estimation of the real behaviour of the dam body. From the compilation of reported failures the conclusion was that the current design criteria are adequate. However, the real challenge lies in ensuring that the construction of dams is correctly performed to fulfil the stated criteria. A transition to Eurocode appears to be reasonable for the stability criterion. A modification of the partial factors is nevertheless necessary to obtain result corresponding to RIDAS, especially for the overturning criteria. / För att uppnå säkra dammkonstruktioner, för alla lastkombinationer, dimensioneras dammar enligt bestämda brottvillkor som ska uppfylla en viss säkerhetsfaktor. Idag används RIDAS, för dimensionering av dammar i Sverige. RIDAS Kraftföretagens riktlinjer för dammsäkerhet, är baserat på BKR, Boverkets konstruktionsregler. I Sverige dimensioneras dammar för att motstå de två globala brottmoderna glidning och stjälpning. Frågan som behöver besvaras är om det finns eller kan finnas några kombinationer av brottmoder som borde beaktas vid dimensionering av dammar. 2009 antogs Eurokoderna och trädde i kraft 2011. Eurokoderna har ersatt BKR vid dimensionering av de flesta konstruktioner i Sverige. I Eurokod används partialkoefficienter för att garantera säkra konstruktioner. Syftet med denna rapport var att undersöka om dagens brottkriterium är tillräckliga för att beskriva hur dammar går till brott. Rapporten behandlar även möjligheten att övergå från att dimensionera dammar enligt RIDAS till att dimensionera enligt Eurokod. För att besvara detta genomfördes en litteraturstudie av rapporterade dammbrott. Dessutom genomfördes analytiska beräkningar för flera olika typer av dammar med varierande geometri och lastfall. Programmen CADAM och BRIGADE användes som ytterligare verktyg för att analysera brottmoderna. Enligt resultat från de analytiska beräkningarna tillsammans med FE-beräkningarna ansågs limit turning inträffa och genererade i högre grad en lägre säkerhetsfaktorer i jämförelse med stjälpning. Limit turning kan förklars som delvis stjälpande och inkluderar brott av bergmassan. Brottmodet är dock beroende av kvalitéten hos berget och det krävs undersökningar av grunden för att kunna göra en god uppskattning av dammens verkliga beteende. Sammanställningen av tidigare brott visade att nu gällande brottkriterier är lämpliga och troligtvis tillräckliga. Utmaningen är istället att säkerställa att konstruktionerna är korrekt utförda och därmed uppfyller dessa brottkriterier. En övergång till Eurokod tycks vara möjlig för de globala brottmoderna, dock är det väsentligt att partialkoefficienterna justeras för att uppnå resultat som överensstämmer med RIDAS, särskilt för stjälpning.

Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro / Estudos de fundações de obras de arte, como barragens de concreto-gravidade e barragens de terra, devem contemplar todos os esforços atuantes no maciço de fundação, principalmente as tensões e as deformações esperadas durante todo o processo construtivo e no período pós-construtivo. Quando essas estruturas são apoiadas sobre rochas de boa sanidade, a escolha do barramento geralmente favorece a implantação de barragens de concreto. Entretanto, quando os maciços de fundação são formados por solos, a opção técnica geralmente mais bem aceita é quanto à utilização de barragens de terra. Em ambos os casos, as análises de estabilidade e de deformação são desenvolvidas por métodos analíticos bem consolidados na prática. Nas condições mais adversas de fundação, seja em rochas ou em solos com marcante anisotropia e estruturas reliquiares herdadas da rocha-mãe, a utilização de modelos constitutivos anisotrópicos em análises por elementos finitos propicia simulações mais realistas dessas feições estruturais, contribuindo para o seu melhor conhecimento. O presente trabalho teve por objetivo demonstrar a utilização de um modelo constitutivo anisotrópico no estudo da fundação da Barragem San Juan, localizada na República Dominicana, que foi concebida como uma estrutura tipo concreto-gravidade apoiada sobre solos residuais jovens altamente anisotrópicos. Nessa obra, apesar de sua pequena altura, a presença marcante de descontinuidades ensejou um estudo mais detalhado do comportamento tensão-deformação da fundação, levando em conta o levantamento detalhado da atitude das descontinuidades presentes no maciço e os resultados de ensaios de resistência em planos paralelos e normais às descontinuidades. Para a estimativa de deformações, os respectivos módulos de Young (Es) foram estimados com base em correlações com a resistência à penetração SPT desenvolvidas nesta dissertação, a partir de um estudo estatístico baseado em várias publicações disponíveis na literatura. As análises numéricas por elementos finitos foram desenvolvidas através do programa Plaxis 2D, utilizando-se como modelo constitutivo aquele denominado The Jointed Rock Model, que é particularmente recomendado para análises de estabilidade e deformação de materiais anisotrópicos. Os resultados das análises numéricas foram comparados com as análises de equilíbrio limite elaboradas para o projeto executivo da referida barragem, pelo programa Slope, utilizando o método rigoroso de Morgenstern e Price, que se mostrou conservador. Os resultados das análises numéricas mostraram sua inequívoca versatilidade para a escolha de opções de reforço da fundação, através de dentes que objetivavam o aumento das condições de estabilidade da barragem.

Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro / Estudos de fundações de obras de arte, como barragens de concreto-gravidade e barragens de terra, devem contemplar todos os esforços atuantes no maciço de fundação, principalmente as tensões e as deformações esperadas durante todo o processo construtivo e no período pós-construtivo. Quando essas estruturas são apoiadas sobre rochas de boa sanidade, a escolha do barramento geralmente favorece a implantação de barragens de concreto. Entretanto, quando os maciços de fundação são formados por solos, a opção técnica geralmente mais bem aceita é quanto à utilização de barragens de terra. Em ambos os casos, as análises de estabilidade e de deformação são desenvolvidas por métodos analíticos bem consolidados na prática. Nas condições mais adversas de fundação, seja em rochas ou em solos com marcante anisotropia e estruturas reliquiares herdadas da rocha-mãe, a utilização de modelos constitutivos anisotrópicos em análises por elementos finitos propicia simulações mais realistas dessas feições estruturais, contribuindo para o seu melhor conhecimento. O presente trabalho teve por objetivo demonstrar a utilização de um modelo constitutivo anisotrópico no estudo da fundação da Barragem San Juan, localizada na República Dominicana, que foi concebida como uma estrutura tipo concreto-gravidade apoiada sobre solos residuais jovens altamente anisotrópicos. Nessa obra, apesar de sua pequena altura, a presença marcante de descontinuidades ensejou um estudo mais detalhado do comportamento tensão-deformação da fundação, levando em conta o levantamento detalhado da atitude das descontinuidades presentes no maciço e os resultados de ensaios de resistência em planos paralelos e normais às descontinuidades. Para a estimativa de deformações, os respectivos módulos de Young (Es) foram estimados com base em correlações com a resistência à penetração SPT desenvolvidas nesta dissertação, a partir de um estudo estatístico baseado em várias publicações disponíveis na literatura. As análises numéricas por elementos finitos foram desenvolvidas através do programa Plaxis 2D, utilizando-se como modelo constitutivo aquele denominado The Jointed Rock Model, que é particularmente recomendado para análises de estabilidade e deformação de materiais anisotrópicos. Os resultados das análises numéricas foram comparados com as análises de equilíbrio limite elaboradas para o projeto executivo da referida barragem, pelo programa Slope, utilizando o método rigoroso de Morgenstern e Price, que se mostrou conservador. Os resultados das análises numéricas mostraram sua inequívoca versatilidade para a escolha de opções de reforço da fundação, através de dentes que objetivavam o aumento das condições de estabilidade da barragem.