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This paper aims at compiling the most relevant information concerning the use of cement-based mortars and concretes in the rehabilitation, retrofitting, and strengthening of hydraulic structures, namely concrete dams. The most important properties of cementbased mortars and concretes as repair materials are addressed, with a special focus on its compatibility with the concrete substrate. After a brief allusion to generic preparatory works, some of the most common practices are described. The main topics are mortar and concrete toppings, i.e., patches and overlays and thickening of the dam section. Among overlays, shotcrete and underwater works are addressed in detail. Littlerock, Oberems, and Storfinnforsen dam interventions are briefly described as successful rehabilitations involving the shotcrete method, whereas the Albbruck-Dogern dam intervention is given as an example of effective underwater repair works. As for dam section modifications, Kölnbrein, Olef, and Sasanagare dams are presented as conventional mass concrete placements within rehabilitation operations, while Les Toules, Gibraltar, Santa Cruz, and Littlerock dams are references for roller compacted concrete strengthening.

Injecting discontinuities is a recurrent procedure for the rehabilitation of concrete hydraulicstructures, namely repairing cracked dam bodies and deteriorated lift and contraction joints.Within this scope, a relatively detailed description of the most important cement injectiongrouts features is presented, including the main advantages and drawbacks compared toalternatives. The cement-based grouts are among the most utilised materials in these contexts.Economic and environmental related aspects are among the main advantages ofcement-based grouts, although some technical features of these grouting materials are alsofavourable. The equipment utilised for the preparation and for the application of cementitiousgrouts is also mentioned. This document also addresses aspects related to the assessment ofconcrete dams

Evaluation of the sliding stability of concrete dams requires the use of numerical tools notonly able to simulate the coupled hydromechanical behavior but also able to adequately represent thefoundation discontinuities and the specific features of dam foundations. The formulation of a threedimensional (3D) small displacement finite element model based on interface elements to simulatethe discontinuities is presented. In this model, the hydraulic behavior is simulated assuming that thewater flow occurs only along channels located at the edges of the triangular interface elements thatsimulate the discontinuities. The model is used to perform coupled hydromechanical analysis of alarge arch-gravity dam and to assess safety against dam base sliding, assuming different constitutivemodels at the dam/foundation interface and two different approaches: (i) strength reduction methodand (ii) amplification of the hydrostatic pressure, assuming an increase in the reservoir level. Thepresent study shows that consistent results are obtained with the proposed numerical model andthat stability analysis should preferably be carried out using the method of increasing the hydrostaticpressure and the corresponding uplift pressures, as this methodology leads to significantly lowersafety factors.

The main aim of structural safety control is the multiple assessments of the expected dam behaviour based on models and the measurements and parameters that characterise the dam’s response and condition. In recent years, there is an increase in the use of data-based models for the analysis and interpretation of the structural behaviour of dams. Multiple Linear Regression is the conventional, widely used approach in dam engineering, although interesting results have been published based on machine learning algorithms such as artificial neural networks, support vector machines, random forest, and boosted regression trees. However, these models need to be carefully developed and properly assessed before their application in practice. This is even more relevant when an increase in users of machine learning models is expected. For this reason, this paper presents extensive work regarding the verification and validation of data-based models for the analysis and interpretation of observed dam’s behaviour. This is presented by means of the development of several machine learning models to interpret horizontal displacements in an arch dam in operation. Several validation techniques are applied, including historical data validation, sensitivity analysis, and predictive validation. The results are discussed and conclusions are drawn regarding the practical application of data-based models.

Some successful rehabilitation schemes involving the use of cement-based grouts for the repair of cracks in concrete dams are described. The author reviews the advantages and drawbacks of using cement-based materials in the context of the four main types of concrete dams (gravity, buttress, arch and multiple arch-buttress structures). These and other successful case studies can serve as guidance for future rehabilitation schemes.

The lifetime of a geothermal well is strongly dependent on the long-term performance of the cement used for its construction. The critical zones in well cements are the outermost layers, where the cement encounters either the steel casing or the rock formation. The current paper presents a study of the changes in the interfacial transition zone that forms between geothermal cements and volcanic rocks, after hydrothermal treatment at 290°C. Cement slurries were poured into cavities drilled into ignimbrite blocks and allowed to set at 90°C. The assemblages were autoclaved under typical geothermal conditions, both with and without a carbon dioxide overpressure at 290°C. The addition of silica to the cement dictates the phases that form in cement. When exposed to carbon dioxide, these calcium silicate hydrate phases carbonate, at distinct carbonation rates. The rate at which these phases form and/or carbonate affects the reaction extent of the cement with the rock and, eventually, the cement durability.

The limited durability of the cement in acidic fluids is one of the main issues controlling the lifetime of a geothermal well. The most critical region is the outermost layer of the cement adjacent to the formation.This paper provides insight into the way in which well cementing formulations interact with a common rock formation in geothermal environments, at 150

Detailed models of concrete mesostructure can be used to understand the interactions between its components and predict complex deterioration scenarios. The discrete or distinct element method (DEM) is currently being used for modeling the fracture process of quasibrittle materials, such as rock and concrete. An explicit formulation of a DEM contact model that includes aging viscoelastic behavior based on the solidification theory is proposed, allowing the DEM particle model to be applied to delayed concrete analysis. Because of thetimestep constraints of the DEM, a fast numerical procedure for the analysis of long-term aging viscoelastic behavior of concrete is also proposed. A calibration procedure for the aging viscoelastic contact model parameters is presented, including new expressions for the delayed deformability macro properties. The presented validation tests using a one-contact particle assembly show good agreement between the fast numerical procedure, the fully explicit DEM procedure with small timestep, and the creep compliance analytical solution. The contact aging model validation tests using larger regular and random particle assemblies show that the fast numerical procedure significantly reduces the computational costs by introducing large timesteps in which the solution is computed while giving the same accuracy as the fully explicit procedure. The DEM aging concrete model is validated using a B3 model fit to Ward et al.

Temperature plays a significant part in the cracking phenomenon of mass concrete structures, and thereforethermal analysis is of major importance, especially during construction, due to the heat of hydration of thecement. A transient coupled 3D finite element analysis of the thermal behaviour of Alqueva dam during con-struction is presented in this paper. The method used for the thermal analysis is described in detail, along with the simulation of the different actions. The thermal state of the dam is affected not only by climatic actions but also by concrete

The rock type plays a key role in the way in which the outermost layer of the cement interacts with the formation, in wells under geothermal environments. The penetration of cement into the rock is controlled by the porosity of the rock which also regulates the amount of CO2 enriched brine that can contact the cement.Samples were prepared by drilling holes into rock blocks, pouring in a cement slurry and hydrothermally treating the whole assembly at 150 °C under typical geothermal environments. The changes in the interfacialtransition zone (ITZ) that forms between geothermal cements and volcanic rocks were examined.Both porosity and the volcanic glass content of the rock have a considerable impact on the way in which thecement and the formation interact and, ultimately, affect the bond between these materials. The porosity has a major influence on the durability of the cement in carbonated brine.

A monitorização de estruturas em Portugal tem sofrido desenvolvimentos significativos nas últimas décadas, na sequência da valorização das vantagens, a curto e longo prazo, da observação e do controlo da segurança das obras. Com esse fim, têm sido introduzidos no mercado dispositivos que recorrem à tecnologia de fibra ótica para a monitorização de obras de engenharia civil.O objetivo deste estudo foi a comparação do desempenho de diferentes dispositivos de medição de extensões do betão. Para isso foram moldados provetes de betão de pontes e de betão de barragens, nos quais foram inseridos diferentes tipos de extensómetros disponíveis no mercado. A comparação foi feita através da diferença entre as extensões medidas em cada extensómetro e as extensões calculadas a partir das medições realizadas em trandutores de deslocamento dispostos nas faces durante ensaios de módulo de elasticidade.Os dispositivos em estudo foram extensómetros de corda vibrante, extensómetros do tipo FSG (resistência elétrica - full-bridge) e extensómetros de fibra ótica, embebidos em betão de pontes e extensómetros do tipo Carlson e extensómetros de fibra ótica, inseridos em em betão de barragens.A utilização de extensómetros de fibra ótica para os dois tipos de betão revelou o bom funcionamento e fiabilidade destes sensores face a diferentes condições, viabilizando uma futura utilização em obra, tanto em pontes como em barragens.

Antes da sua aplicação, tanto em obra como em provetes laboratoriais, requere-se a calibração dos dispositivos de resistência elétrica do tipo Carlson, nomeadamente extensómetros e medidores do movimento de juntas, a embeber no seio do betão. Essa calibração é realizada com recurso a sistemas mecânicos, correntemente designados por prensas de teste e calibração, constituindo padrões de referência que asseguram a rastreabilidade das medições. Atualmente não são conhecidas soluções comerciais fiáveis adequadas a este fim, pelo que houve necessidade de desenvolver um equipamento específico para o efeito.Em termos de desempenho pretende-se, no caso dos extensómetros correntes de 254 mm (10

This paper presents a study on seepage in a gravity dam foundation carried out with a view to evaluating dam stability for the failure scenario of sliding along the dam/foundation interface. A discontinuous model of the dam foundation was developed, using the code UDEC, and a fully coupled mechanical-hydraulic analysis of the water flow through the rock mass discontinuities was carried out. The model was calibrated taking into account recorded data. Results of the coupled hydromechanical model were compared with those obtained assuming either that the joint hydraulic aperture remains constant or that the drainage system is clogged. Water pressures along the dam/foundation interface obtained with UDEC were compared with those obtained using the code DEC-DAM, specifically developed for dam analysis, which is also based on the Discrete Element Method but in which flow is modelled in a different way. Results confirm that traditional analysis methods, currently prescribed in various guidelines for dam design, may either underestimate or overestimate the value of uplift pressures. The method of strength reduction was used to estimate the stability of the dam/foundation system for different failure scenarios and the results were compared with those obtained using the simplified limit equilibrium approach. The relevance of using discontinuum models for the safety assessment of concrete dams is highlighted.

The safety of the system formed by the dam, its foundation, the reservoir, and the downstream area of the dam should be evaluated on its structural, hydraulic, operational and environmental components.In particular, the structural safety assessment of an existing dam is based on the establishment of correlations between the main loads, its structural properties, and its structural responses. The values of observed responses are compared to predicted values obtained by structural behaviour models or by historical observations.Over the years, new developments in technological devices have been introduced in this field, namely through the implementation of automated data acquisition systems. This evolution, associated with very important progresses in information systems technology, has raised new challenges, but has also provided new opportunities, such as the development of data management systems that allow the person responsible for dam safety to access data, interpret the information, and make decisions, as quickly as possible.The National Laboratory for Civil Engineering (LNEC) has developed the GestBarragens system, which was designed and developed using a modular approach, based on a common data architecture that can be accessed through a Web interface.This paper intends to show the improvements that the GestBarragens system provides to the activities related to the safety control of more than one hundred large concrete and embankment dams, including the observation of several physical quantities measured by the monitoring systems, the interpretation of the information and the transmission of warnings to the entities responsible for the dam

A Nova Barragem do Alto Ceira, atualmente em construção, é uma barragem abóbada, em betão, com 41m de altura e 133m de comprimento no coroamento, situada na zona centro de Portugal. A necessidade de construção da nova barragem prende-se com a substituição da existente, situada cerca de 200m a montante, a qual se encontra significativamente degradada devido a fenómenos de expansão do betão. Como é usual, o projeto da nova barragem engloba um plano de observação elaborado de acordo com o Regulamento de Segurança de Barragens, sendo a instrumentação embebida no betão baseada em sensores elétricos convencionais, em utilização há várias décadas.Os recentes desenvolvimentos da monitorização estrutural com base na fibra ótica, beneficiando nãosó da elevada precisão, durabilidade, e possibilidade de multiplexagem dos sensores óticos, mastambém da facilidade de transmissão do sinal e comunicação da fibra ótica, evidenciam grandespotencialidades na sua aplicação a barragens. Com esse objetivo, novos transdutores em fibra óticaforam desenvolvidos e instalados, numa base experimental, na Nova Barragem do Alto Ceira. Tendoem consideração que os sensores embebidos no betão em massa são dos mais expostos à agressividadedos métodos construtivos de barragens, foram selecionados para implementação novos transdutores dedeformação, de temperatura e de juntas, baseados nas redes de Bragg em fibra ótica, com o objetivo deavaliar o seu desempenho, fiabilidade e requisitos de instalação. Assim, de um modo pioneiro, foramconcebidos e construídos em laboratório, e instalados em obra um número limitado destes sensores.Neste artigo, são apresentados os novos sensores e as condições de instalação na barragem, bem comoresultados da calibração e de comparação com os sensores elétricos tradicionais, quer em condiçõescontroladas de laboratório, quer em condições de obra.

The New Alto Ceira Dam is a concrete arch dam, 41 m high and 133 m long at the crest, located in the middle region of Portugal. Its objective is the replacement of the existing dam located about 200 m upstream, which is highly deteriorated due to swelling phenomena.The dam is actually under construction and its monitoring safety plan is in accordance with the Portuguese Safety Regulations on Dams. The instrumentation embedded into the concrete is based on traditional electrical devices developed several decades ago and with proved durability characteristics.Considering the recent improvements in fiber optic based instruments for structural monitoring, benefiting of multiplexing technique, great reliability and accuracy, it was decided, in an experimental frame, to develop and to install in the New Alto Ceira Dam a set of fiber optic devices.Assuming the instruments embedded into the concrete mass as those exposed to the most aggressiveness of the construction methodologies, strain meters, thermometers and joint meters were selected to the development and implementation of fiber Bragg grating based transducers in order to appraise their performance, reliability, and installation requirements. After laboratory testing and validation, a limited number of these type of transducers were installed in the New Alto Ceira Dam.In this paper, the results from calibration tests are presented, and then a comparison of performance between new fiber optic sensors and the traditional electric sensors is made under controlled conditions, in laboratory. Some preliminary results of the experimental monitoring of the dam are also illustrated.

The current study has investigated the interactions betweenwell cements and one of the most common types of rocks foundin geothermal environments, under hydrothermal conditions.Holes were drilled in blocks of ignimbrite rock and API classG cement with 0, 20 and 40% added silica flour, was poured intothe cavities. The whole assemblage was autoclaved, under typicalgeothermal conditions at 150° and 300°C for 28 days.The results show that chemical reactions occur in the intertransition zone, which are dependent on both drilling fluid andtemperature. The use of bentonite as a drilling fluid and the exposure to higher temperatures (300°C) when compared to 150°C,seem to exacerbate the reactions occurring in the ITZ. Consequently, there is formation of new crystalline products, whichhave worse performance when the physical bonding between thecement and the rock is considered.The effect of other variables such as CO2 exposure, the hydrothermal alteration of the rock and the curing time are currentlybeing investigated within this research project.

Dam safety control activities require an accurate knowledge of each specific dam, with the purpose ofdefining and justifying the judgment about its safety. This task is mainly supported by the cross validationbetween simulation models, measurements provided by the monitoring systems, and the parameters thatcharacterize the dam's behaviour. The main issue is the assessment of the actual structural behaviour in realconditions, which can be used to detect any anomaly and/or malfunction in advance.Over the years, we can verify a significant evolution in the process of interpreting the physical quantitiesprovided by dam monitoring systems. Nowadays, automated data acquisition systems have become a realityin several dams. These systems can be used to support the analysis for dam safety assessment in real time,but also lead to the increase of requirements related to the management, processing and analysis of largeamounts of data.With the development of information systems to support the activities related to dam safety control,particularly the management of a large quantity of information, new challenges related to the managementand analysis of information in real time are raised.The implementation of an Internal Early Warning System (IEWS) based on the automatic analysis of a largequantity of data in real time allows the early identification and notification of potential abnormal situations andmakes the person responsible able to focus on other activities related with the dam safety control of dams.This paper addresses a proposal for an IEWS able to generate warnings in real time when non-accordancebetween observed and predicted values is verified. Subjects related to the definition of the thresholds forquantities measured by the monitoring system, as well as the notification process to the person responsiblefor the dam's safety control, are also discussed.This paper presents the actual Portuguese experience. Aspects related with the requirements for the IEWSare approached. Threshold definition with quantitative interpretation models based on statistical methods,such as multiple linear regression models, and artificial neural network models, is discussed.

This paper presents the most relevant monitoring data and the interpretation of the structural behaviour of Alqueva dam during the first filling of the reservoir, which took place between February 2002 and January 2010.The safety control and the interpretation of the dam

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.

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