Publications

The application of the limit state design (LSD) in the geotechnical area has increased over the last two decades, but this approach is not yet widely used in dam safety evaluation. This study aims to widen the use of the LSD application for large dams, in particular concrete gravity dam foundations. This paper starts with a brief reference to the LSD approach in recently published guidelines for dam design, followed by a detailed description of the LSD formulation when applied to the foundation of concrete dams. The relevance of the joint application of the concepts of ultimate limit states and of numerical methods is highlighted. Comments are made regarding the criteria adopted in order to determine the characteristic values of the material mechanical properties, with an emphasis on discontinuities, taking into account the spatial variability. The sliding safety assessment of the foundation of a concrete gravity dam using the LSD and a discrete element model, both in persistent and in an accidental design situation, is presented. Results led to the conclusion that the LSD methodology may be followed for dam foundation design with the partial factor values prescribed in Eurocode 7.

To improve the effectiveness of concrete dam safety control in real time, a method is presented for theconstruction of decision rules for the early detection of developing failure scenarios. The decision rulesare based on the use of linear discriminant models developed with data obtained through mathematicalmodels of the dam

In its lifetime, a dam can be exposed to significant water level variations and seasonal environmental temperature changes. The structural safety control of a concrete dam is supported by monitoring activities and is based on models.In practice, the interpretation of recorded concrete dam displacements is usually based on HST (hydrostatic, seasonal, time) statistical models. These models are widely used and consider that the thermal effect can be represented by a seasonal function. The main purpose of this paper is to present an HTT (hydrostatic, thermal, time) statistical model to interpret recorded concrete dam displacements. The idea is to replace the seasonal function with the use of recorded temperatures that better represent the thermal effect on dam behavior.Two new methodologies are presented for constructing HTT statistical models, both based on principal component analysis applied to recorded temperatures in the concrete dam body. In the first method, principal component analysis is used to choose the thermometers for the construction of the HTT model. In the second method, the thermal effect is represented by the principal components of temperature of selected thermometers.The advantage of these methods is that the thermal effect is represented by real temperature measured in the concrete dam body. The HTT statistical models proposed are applied to the 110m high Alto Lindoso arch dam, and the results are compared with the HST displacement model.

The purpose of this research work is to identify the effect of the daily variation of the air temperature on the structural response of a concrete dam. It is intended to obtain a better knowledge about structuralbehaviour of concrete dams. In current day to day activities, quantitative interpretation models are used for the assessment of structural dam behaviour of concrete dams. Most models ignore the temperature effect of a wave with a daily variation. However, in dams with automated data acquisition systems this daily effect can be used to anticipate the detection of abnormal behaviour.In this paper, the Short Time Fourier Transform analysis of the residuals is used, obtained by the quantitative interpretation models and measurement data, to identify the signature that the daily variation of the air temperature has on the structural behaviour of a concrete dam. A case study is presented based on the analysis of a horizontal displacement measured on a pendulum, in the Alto Lindoso concrete dam. As a result, the relation between magnitudes of daily variations of the horizontal displacement analysed and the air temperature was defined. The relation obtained can be used to assess if there is alterations or not in the dam response to short period loads corresponding to the daily variations analysed.

This paper presents the application of a methodology which can be used to assess arch dam foundation stability, using the discrete element method (DEM) and the code 3DEC. A global three-dimensional model of a dam foundation was developed, in which some discontinuities were simulated and both the grout and drainage curtains were represented. The model, calibrated taking into account recorded data, was used to carry out non-linear mechanical analysis. The same model was employed to perform a hydraulic analysis, based on equivalent continuum concepts, which allowed the water pressure pattern within the foundation to be obtained. These water pressures were applied on discontinuities involved in the possible sliding mechanism along the dam/foundation interface, and the safety of the dam/foundation system was evaluated using a process of reduction of strength characteristics, with the aim of calculating the minimum safety factors that ensure stability. Results were compared with those obtained with the usual bi-linear uplift pressure distribution at the base of the dam, commonly used in concrete dam design. The relevance of carrying out hydraulic analysis in arch dam foundation failure studies is highlighted.

Neste trabalho apresenta-se a aplicação de uma metodologia que pode ser usada para avaliar a segurança de barragens abóbada relativamente a estados limites últimos envolvendo a fundação. É usado o método dos elementos discretos e o programa 3DEC. Apresenta-se um modelo global da barragem e fundação, com o qual é possível efetuar análises mecânicas e análises hidráulicas. No modelo são representadas três das cinco principais famílias de descontinuidades do maciço e outras superfícies de descontinuidade, tais como a superfície de fundação e as juntas de contração da barragem. A influência da pressão da água na fundação na estabilidade de uma cunha do maciço a jusante da obra é analisada comparando os resultados obtidos sem subpressões, com os obtidos aplicando as pressões calculadas com o modelo hidráulico ou aplicando campos de pressões simplificados, definidos a partir de uma superfície freática compatível com as condições de fronteira.

One of the most important phenomena of the delayed behaviour of mass concrete used in dams is creep, i.e., the increase in deformation over time when subjected to constant stress. Although several studies concerning concrete creep were carried out throughout the last decades in a structural and material level, the physical and chemical phenomena are yet to be fully understood. This paper presents a study on the Alqueva dam

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Borehole water-inflow tests allow measurement of discharges and water pressures in isolated sections of drains and piezometric boreholes. A series of water-inflow tests and water electrical conductivity analysis were carried out in an area of the foundation of an arch dam. Detailed three-dimensional numerical models developed for the analysis of the tests data in two foundation areas are presented. Results of rock mass permeability tests and areas where seepage paths cross each drain, identified with both water-inflow tests and water electrical conductivity analysis, were taken into account. Models were validated against flow rates and water pressures recorded in situ. By examining water-inflow tests using numerical models, the main flow processes are identified and quantified. Test results and conclusions drawn from the detailed 3D models were used to elaborate a global model of the foundation. The present study shows that borehole water-inflow tests add valuable information to the usual monitoring data, which improves our ability to analyse the behaviour of concrete dam foundations. It is also concluded that although discontinuum models provide a more natural representation of flow in jointed rock masses, equivalent continuum models can still be used successfully to study both global and local hydraulic behaviour of dam foundations.

Recycled aggregates may make an important contribution toward decreasing the adverse consequences of the production and the dumping of construction and demolition waste CDW on the environment. The results of the experimental research work carried outat Lisbon

The use of cement based mortar and concrete for repair, rehabilitation and retrofitting of concrete dams is a relatively common practice, due to both technical and economic reasons. This paper aims at compiling some of the most relevant information concerning this topic, including references to successful case histories.Firstly, mortar or concrete patches, whose objective is typically to fix the problem with a relatively small volume of repair material. This technique is a popular solution solution for damaged surfaces due to abrasive actions. The following procedures are the concrete overlays, which typically involve more material and complexity than a patch. Finally, the cross sections thickenings, which necessarily imply a large volume of repair concrete. Different types of overlays and cross section enlargements are shown.The shotcrete technique is briefly described as an overlay technique. Conventional concrete casting is referred here as either an overlay technique or a method for increasing the cross section of a concrete dam. The common need of carrying out rehabilitation measures on the upstream face without drawing down the reservoir is considered in the subchapter underwater works. Finally, the roller compacted concrete, which is, probably, the most frequently used method for increasing the dam section. Some of these techniques are typically combined during as part of rehabilitation or retrofitting processes.

This paper presents the main characteristics of the automated data acquisition system of BaixoSabor dam and the quality assessment of ADAS carried out by comparation of automatic andmanual measurements.Baixo Sabor is 123 m high concrete arch dam, and 505 m long at the crest, designed, constructedand explored by EDP, located in the northeast of Portugal in Sabor river (a tributary of Douro river).The first filling of its reservoir, with a volume of about 1095 hm3, took place between December2013 and April 2016.In operation since August 2016, the ADAS of the Baixo Sabor dam allows the measurement ofseveral physical quantities used for the safety control, analysis and interpretation of the dambehaviour, such as: horizontal and vertical displacements, movements of joints, strain, upliftpressure, foundation displacements, seepage, concrete and air temperatures, and reservoir waterlevel, among others.The assessment to the ADAS quality measurements was performed through the analysis of pairedsamples with manual readings. For this purpose, comparison graphs and statistical values (means,variances, and correlations) of the two sets of quantities were generated.The analysis of this information has shown the existence of deviations from ADAS measurementsthat were classified into three types: zero scale errors (shift values), sensitivity errors and atypicalvalues.Based on this analysis, the ADAS databases were corrected and a mechanism for filteringanomalous values was implemented. These measures allowed to ensure the correct operation ofthe ADAS of Baixo Sabor dam.

The assessment of the structural safety and serviceability of concrete dam is often supported by the use of models. The analysis and interpretation of the observed structural responses, such as displacements, is usually performed through the comparison with values obtained by statistical models, mainly multiple linear regression models, which are also known as quantitative interpretation models. Nowadays, several new machine learning models have been used for the assessment of the concrete dams

This document aims at compiling a considerable number of successful rehabilitation examples involving the use of cement based grouts in the repair of cracks in concrete dams and its content is based on information that was previously published.This article starts with a brief introduction regarding the use of cement based grouts in the injection of cracks in concrete dams, in which advantages and drawbacks of the use of cement based materials within this scope are discussed. In the same context, particularities of the main four structural types of concrete dams, i.e. gravity, buttress, arch and multiple arch-buttress, are also addressed.Each one of the following four chapters are focusing on the above mentioned types of concrete dams. The chapter three presents two examples of concrete gravity dams that were successfully rehabilitated. Considerable seepages were detected in both gravity dams presented. In Isle-Maligne dam, leakages in horizontal construction joints occurred due to leaching and freeze-thaw cycles, whereas deterioration of Kuromata dam was mostly caused by ageing. In chapter four, three buttress dams are given as examples: Big Eddy, Pracana and Storfinnforsen dam. The Big Eddy dam showed leaching of horizontal construction joints caused by open lift joints. Pracana, on the other hand, had degraded faces and cracks provoked by swelling reactions. Storfinnforsen exhibited cracking and spalling as well as leakage. Chapters five and six are solely focused on one case history each: the Bimont arch dam and the Daniel-Johnson arch-buttress dam respectively. Bimont was subjected to swelling reactions, which resulted in cracking. Daniel-Johnson dam also cracked considerably, although due to different causes: the geometry of the structure and thermal stress. All the cases were resolved with cement grouting combined with other repair materials and measures, such as epoxy resin, shotcrete, installation of geomembrane or grouting of contraction joints.These and other successful rehabilitation operations should serve as guidance in comparable upcoming rehabilitation operations, involving grouting of concrete dams with cement based materials.

Foz Tua dam, located close to Tua river

Seepage through the foundation is a relevant condition for the structural assessment of concrete dams. The knowledge of the water flow measured in the drainage system installed to reduce the uplift pressure in a dam's foundation is, therefore, a main issue in the safety control of concrete dams. Monitoring systems include measuring devices to determine the water collected from drains and weirs in order to evaluate the amount of water that flows through the dam. In most large concrete dams, both manual and automated water flow measurements are possible.This paper proposes a statistical quality control method for automatic measuring systems based on simultaneous manual water flow measurements and the knowledge of the corresponding measurement uncertainties. Experimental tests performed in a weir of a Portuguese concrete dam are described and paired water flow estimates and corresponding measurement uncertainties are presented and applied to the proposed method. The results of this study show that the method allows statistical quality control of automated water flow measurement systems applied in concrete dam drainage systems.

Foz Tua project, located close to Tua river

Cement based grouts are commonly used for injections in concrete dams as part ofrehabilitation operations of cracked dam bodies and degraded contraction joints.This document addresses aspects such as assessment of the dam

The explicit formulation of a small displacement model for the coupled hydro-mechanical analysis of concrete dam foundations based on interface finite element technology is presented. The proposed 3D hydromechanical coupled model is based on a 2D coupled model that has been recently proposed. This 3D model, as in the 2D version, requires a thorough pre-processing stage to ensure that the interaction between the various blocks which represent the rock mass foundation and the dam is always face to face. The mechanical part of the model, though limited to small displacements, has the advantage of allowing an accurate representation of the stress distribution along the interfaces, such as rock mass joints. The hydraulic part and the mechanical part of the model are fully compatible. The verification and application examples presented in this paper show that the proposed 3D hydromechanical coupled model allows seepage flow through rock masses to be accurately simulated.

A exploração de grandes barragens envolve, em regra, riscos elevados. Por essa razão exige-se um acompanhamento cuidado destas obras, tendo a observação (monitorização, inspeção e ensaios) um papel fundamental nas atividades de controlo da segurança. Os sistemas de observação das barragens incluem, em regra, dispositivos para monitorização de grandezas relacionadas com as ações e com asrespostas térmica, estrutural e hidráulica do conjunto barragem-fundação. A definição destes sistemas é balizada pela regulamentação portuguesa de segurança de barragens.Nas barragens do Baixo Sabor e do Feiticeiro, dada a sua dimensão e importância, para além dos dispositivos tradicionais com leitura manual, foram instalados sistemas de monitorização automática, tecnologicamente evoluídos, com vista a aumentar a frequência de leitura das grandezas mais significativas com recolha manual, a avaliar as ações dinâmicas e os seus efeitos estruturais nas barragens e a ultrapassar as dificuldades de instalação de redes de observação geodésica por jusante.Referem-se os sistemas de recolha manual e os quatro sistemas específicos de monitorização automática, designadamente o RAD (recolha automática de dados), complementar à recolha manual, envolvendo 232 dispositivos e 407 grandezas, o GNSS (Global Navigation Satellite System), destinado à medição de deslocamentos absolutos através de 8 recetores em regime permanente, o SOS (sistema de observação sísmica), para registo de eventos sísmicos utilizando 6 estações remotas instaladas nas imediações das albufeiras e 8 estações instaladas nas galerias das barragens, e o SMD (sistema de monitorização dinâmica em contínuo), apenas na barragem do Baixo Sabor, para avaliação da evolução das características dinâmicas (frequências próprias e modos de vibração) a partir da excitação ambiente, usando 20 acelerómetros uniaxiais de elevada sensibilidade.

As inspeções visuais constituem uma atividade importante do controlo de segurança de barragens. O registo continuado de anomalias e ocorrências permite ao dono de obra acompanhar e manter o estado da obra e do sistema de observação e planear eventuais reparações e processos de reabilitação.Atualmente, é prática corrente recorrer a fichas de inspeção visual para o registo das ocorrências em cada elemento estrutural da obra e elaborar relatórios técnicos em que se descreve a evolução do estado de conservação desde a última inspeção.Este trabalho apresenta uma proposta para a implementação BIM a inspeções visuais de barragens de betão com o objetivo de sistematizar e digitalizar a informação proveniente das fichas de inspeção para um modelo BIM tridimensional. Pretende-se que o modelo BIM seja utiliza-do para melhorar a visualização das ocorrências ao longo do tempo.Este trabalho constitui o primeiro passo com vista à criação do sistema integrado BIM de análise de dados gerados automaticamente e de inspeções visuais.Apresenta-se uma proposta de utilização de formulários digitais pré-definidos para o registo das ocorrências e para exportação sistematizada da informação para o modelo BIM tridimensional. Propõem-se as regras de modelação da barragem para a fase de exploração da obra e a definição e classificação de objetos BIM para a estrutura, para as ocorrências e para os instrumentos, incluindo a definição das propriedades para o registo da informação.

Nowadays, organizations are embracing digital transformation, investingin the integration of information and communication technology (ICT) toolsand solutions. Advanced ICT technologies converge with operations technologies(OT), allowing machines, processes, employees, and products to be part ofa single data framework, from data collection to analysis, interpretation, and assessment,which are the foundation for informed decision-making. Industry 4.0takes advantage of emergent ICT to make the right decisions, at the right time,optimizing processes, minimizing risks and improving value chains. The mainaim of the structural safety assessment and control of critical infrastructures, suchas dams and bridges, is to protect people, property and the environment fromharmful effects of failure or misoperation of infrastructures. This goal is achievedthrough Structural Health Monitoring and Control (SHMC) activities to monitorand track the life-cycle of critical infrastructures in such a way that it can providesufficient information for long- and short-term decisions regarding structuralsafety assessment. The objective of this work is to present a reflection of the impactof the industry 4.0 trends on the structural safety assessment of critical infrastructuresand, more specifically, to understand the level of maturity and toshow how the leveraging of enabling technologies such as augmented reality,Internet of Things (IoT), additive manufacturing, cloud computing, big data andanalytics are impacting the SHMC activities on critical infrastructures, which aretraditional cyber-physical systems with complex sensor networks used to assessand control structural safety and health.

As atividades de controlo de segurança de barragens de betão têm um caráter preventivo, com o intuito de facilitar a tomada de decisões de forma atempada para evitar ou minimizar as consequências resultantes de um acidente ou incidente de uma barragem. No controlo de segurança de barragens com sistemas de monitorização automática, a análise de uma grande quantidade de dados ainda pode tornar-se uma tarefa difícil. Por um lado, pretende-se garantir o controlo de segurança, em tempo real, mas, por outro lado, a capacidade humana de processar a informação de dados é limitado. No entanto, os desenvolvimentos tecnológicos em termos de capacidade de processamento de informação têm permitido o desenvolvimento de ferramentas para a análise de grandes quantidades de dados. A necessidade de rever os procedimentos de análise de dados adequados para a extração de informação tornou-se um aspeto importante para a tomada de decisão em tempo útil. Por estas razões, é fundamental proporcionar às entidades responsáveis pela segurança das barragens um sistema de apoio à gestão da informação que facilite o acesso aos dados, a interpretação da informação e a tomada de decisão, de forma atempada. Neste contexto, o principal objetivo desta dissertação é a definição de metodologias para: i) melhorar a qualidade das grandezas medidas pelo sistema recolha automática de dados, através da implementação de procedimentos para o controlo da sua qualidade e para a validação dos resultados, tendo em conta a incerteza de medição dos sistemas de medição; ii) melhorar os procedimentos relacionadas com a análise de dados e a sua interpretação, através de uma abordagem baseada nos dados da observação, a fim de apoiar a decisão de quais as grandezas que devem ser incluídas na sistemas de recolha automática de dados, quantificar o efeito da onda térmica diária na resposta da estrutura e reconhecer padrões de comportamento da barragem; iii) a definição de avisos relacionados com a identificação de comportamento anómalo, e de potenciais cenários de rotura. A aplicação das metodologias propostas num sistema de apoio à gestão da informação será um passo sólido para a melhoria dos processos de controlo de segurança em tempo real.

Apresenta-se um estudo sobre o comportamento de fundações de barragens de betão na fase de exploração normal das obras desenvolvido com o objectivo de validar e fundamentar a aplicação de modelos numéricos de análise do comportamento hidromecânico de maciços rochosos, tendo em vista generalizar a sua utilização e tornar mais eficaz a observação e controlo de segurança destas obras. Foi estudada a representação em modelos numéricos da cortina de impermeabilização e do sistema de drenagem e das condições geológico-geotécnicas concretas das zonas de fundação analisadas, tendo em conta, nomeadamente, os problemas computacionais associados a modelos tridimensionais. Foram realizados ensaios de afluência de água em duas grandes barragens portuguesas, uma gravidade e uma abóbada, que se verificou serem fundamentais para caracterizar o escoamento no maciço, complementando a informação obtida com o sistema de observação. Desenvolveram-se modelos hidráulicos e hidromecânicos do comportamento das fundações destas barragens, que no caso da barragem gravidade foram utilizados no estudo de cenários de rotura. Apresentam-se conclusões sobre a adequação e limitação dos modelos numéricos utilizados, sobre os parâmetros essenciais para calibrar e aplicar esses modelos, e propõem-se métodos de planeamento e utilização dos sistemas de observação de fundações de barragens, de modo a melhorar o controlo de segurança.

O presente trabalho pretende contribuir para o aperfeiçoamento dos modelospara análise do comportamento de barragens de betão ao longo do tempo, submetidasa processos expansivos devidos a reacções químicas de origem interna. Odesenvolvimento destas reacções expansivas, determinado pela composição do betãoe influenciado pelos campos térmico, higrométrico e de tensões, pode provocarfissuração e contribuir para a deterioração precoce das obras.O trabalho aborda, na parte inicial, a fenomenologia dos processos expansivos,salientando-se os factores de natureza física e química que mais os influenciam. Deseguida apresentam-se os aspectos relacionados com a identificação e acaracterização das reacções expansivas, no que respeita às evidências físicas e aosseus efeitos estruturais. Analisam-se, entre outras obras, as barragens portuguesasafectadas por esta patologia.A influência dos factores que regulam o desenvolvimento do processoexpansivo (composição do betão, temperatura, humidade e estado de tensão) équantificada com base num modelo de interacção químico-mecânico, permitindo umaestimativa das expansões à escala das obras de engenharia. Este modelo foiintegrado num código computacional de elementos finitos que considera ocomportamento diferido do betão, através de um modelo viscoelástico com maturação,e o surgimento e propagação da fendilhação, por meio de uma formulação de dano.Utiliza-se uma técnica incremental na discretização das acções que permite simular aevolução do comportamento ao longo do tempo, tendo em conta os fenómenosdiferidos e o progressivo desenvolvimento da fissuração.Apresentam-se dois estudos de aplicação a barragens portuguesas afectadaspor processos expansivos. O primeiro estudo refere-se à barragem de Santa Luzia,uma abóbada construída entre 1939 e 1943, em que a magnitude das expansões émoderada. O segundo estudo reporta-se à barragem de Pracana, uma obra decontrafortes cuja albufeira foi mantida vazia durante mais de uma década após trintaanos de exploração, devido à fendilhação generalizada da sua estrutura provocada porgrandes expansões diferenciais, que depois foi reabilitada, encontrando-se desdeentão em exploração normal há cerca de quinze anos. Os resultados destes estudosdemonstram o interesse e as potencialidades das metodologias desenvolvidas naquantificação do processo expansivo, na interpretação do comportamento observado ena avaliação das condições de segurança das obras.

This work deals with the estimation of the parameters of mixtures of beta variables. The work is organized in four main sections preceded by an introduction and succeeded by conclusions. The second section summarizes the properties of the beta distribution and describes two methods to estimate its parameters from observed samples, the method of moments and the maximum likelihood method. The third section presents the general concept of a mixture of random variables, presents the likelihood function of a sample of a beta mixture, finally, describes the EMA