Publications

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.

The mechanical property characterization of dam concrete is a challenging task mainly due to the use of large aggregate sizes. The properties of dam concrete are often evaluated from wet-screened concrete tests using standard specimen sizes. A physically-based relationship between dam concrete and wet-screened concrete strength properties is currently unavailable.A prediction methodology is proposed which can be used to obtain the compressive and the splitting tensile strength of dam concrete by taking into account the wet-screened strength results, the effect of the specimen dimensions and the effect of the maximum size of aggregate. The predicted results are compared with test results available in the literature and with test results recently obtained during the construction of the Baixo Sabor dam. It is shown that the proposed prediction tool can be used to obtain accurate estimates of dam concrete strength.

The explicit formulation of a small displacementmodel for the coupled hydro-mechanical analysis of concretegravity dam foundations based on joint finite elementsis presented. The proposed coupled model requires athorough pre-processing stage in order to ensure that theinteraction between the various blocks which representboth the rock mass foundation and the dam is always edgeto edge. The mechanical part of the model, though limitedto small displacements, has the advantage of allowing anaccurate representation of the stress distribution along theinterfaces, such as rock mass joints. The hydraulic part andthe mechanical part of the model are fully compatible. Thecoupled model is validated using a real case of a dam inoperation, by comparison of the results with those obtainedwith a large displacement discrete model. It is shown that itis possible to assess the sliding stability of concrete gravitydams using small displacement models under both staticand dynamic conditions.

This paper proposes a methodology for the prediction of the compressive creep strains of dam concrete based on wet-screened experimental results at constant elevated temperature conditions measured in situ. Due to its large aggregate dimensions, the experimental characterization of dam concrete has particular constraints. The wet-screened concrete, obtained by sieving the aggregates larger than a given dimension, after mixing, is used to cast standard specimens and to embed monitoring devices. An experimental in situ installation using creep cells was used to obtain the compressive creep strain development over time for the maturing conditions of the dam core. The study of the effect of wet-screening procedure on creep in compression considers three types of concrete, dam concrete and two wet-screened concretes tested at three loading ages, 28, 90 and 365 days. The comparison between different types of concrete at different maturing conditions requires the definition of a reference state given by the maturity method, using the equivalent age, and relies on the fit of compressive creep strains to the RILEM recommended model B3. To take into account the effect of the aggregate content on the deformability properties of dam concrete, an equivalent two-phase composite model was applied. The equivalent composite model considered the equivalent matrix as the wet-screened concrete and the inclusions as the larger aggregates that are removed during the wet-screening procedure. Predictions obtained with the composite model are close to the dam concrete experimental results, for the tested loading ages.

This paper proposes the use of the maturity method and of a two-phase composite models for the prediction of dam concrete modulus of elasticity.The methodology was validated with test results obtained from experimental in situ setup using creep cells placed in the dam's body, subjected to variable environmental conditions. It is shown that composite models can be used to predict the modulus of elasticity of in situ dam concrete based on the modulus of elasticity of the wet-screened concrete.

The reduced lifetime of geothermal wells is one of the main issues facing the geothermal industry, with cement durability being one of the main causes for shortening of a well's life. While most wells are cemented with American Petroleum Institute (API) class cements, alternative cementing systems are currently being considered. In this paper, the interactions of two alternative cement formulations with a typical geothermal rock formation are compared with a class A cement. This allows understanding of the most critical zone in the geothermal cement, which is the outermost layer where the cement encounters and, consequently, interacts with the exterior harsh environment, including the volcanic formation and brine. The faster setting of white cement and high-alumina cement compared with the well Portland cement seems to reduce the reaction extent with the rock. For all the cements tested, both the increased curing temperature (from 150°C to 290°C) and the use of bentonite as drilling mud significantly decreased the bond between the cement and the rock.

Monitoring is a key activity to ensure the structural safety of dams and is used for detection of deterioration, including local degradation issues and more extensive deterioration scenarios, such as the development of internal expansion reactions which, in the worst case scenario, can lead to severe cracking and even to the abandonment of the dam.This paper presents an overview of an information system that includes a monitoring database, which includes the records of the main actions (water level, air and water temperatures and temperature inside the concrete) and of the main structural responses (radial and tangential displacements measured in inverted plumb-lines and using geodetic techniques, displacements measured in rod extensometers and by precision levellings in target points, joint displacements measured in joint meters, bi- and tridimensional strain fields measured in sets of strainmeters). The hydraulic behaviour of the foundation is also monitored, including the measurement of water discharges along the drainage gallery and the water pressure in the foundation (uplift). The database has monitoring data since the construction period of each dam until this date through periodic readings over the years.Different measurements in some dams, with and without identified deterioration processes, are presented and compared in order to showcase the importance of monitoring activities over the structures lifetime.

This paper presents a methodology for the prediction of dam concrete instantaneous and long-term deformability properties using discrete element method (DEM) based on particle models (PM). The concrete mix, namely the content, size and distribution of the aggregates is explicitly taken into account. This type of concrete has large aggregate size and fraction volume. Due to the computational cost of the analysis of a large number of particles, dam concrete specimen is represented by an arrangement of mortar particles and of coarse aggregates particles. The overall behaviour is determined by the micro properties at each contact type, i.e., mortar-mortar, aggregate-aggregate, and aggregate-mortar which defines the interfacial transition zone (ITZ).The proposed approach is to characterize and model both the mortar and the coarse aggregates separately and study their interaction in the heterogeneous model of concrete. For the mortar, a long-term analysis is required for modelling the aging viscoelastic properties. For the aggregates, an elastic analysis defines the contact micro properties in order to obtain the macro properties of the intact rock.The numerical results obtained from the dam concrete particle model using DEM show a good agreement with the available experimental results for several loading ages.

The Ribeiradio-Ermida multipurpose hydro scheme, built between July 2010 and the end of 2015, is the first major project in the Vouga River basin and is located in the centre of Portugal. Its main purposes are power generation, water supply and flood control. The Ribeiradio dam is a 83 m high concrete gravity dam, with a controlled gated spillway over the dam structure. This project encompasses a second lower dam, Ermida, located 5 km downstream, to regulate Ribeiradio flows. Both schemes are under operation since the first quarter of 2016.This paper presents the main features and results obtained during the first filling of the Ribeiradio dam reservoir and during the subsequent period of exploitation until the end of 2017. In accordance with the Portuguese legislation, the results of the detailed inspections of the dam and its foundation, as well as the integrated analysis of all results provided by the monitoring system, which are presented in the paper, have shown both the dam and its foundation present a satisfactory behaviour.

The failure of dams with large reservoirs can be the cause of catastrophic accidents with very important losses of human lives, material and environmental assets. For these reasons, the safety control of these constructions is regulated and followed by national authorities, considering the structural, hydraulic-operational and environmental aspects. In Portugal, the national authority is technically assisted, for dams that involve major risks, by the National Laboratory for Civil Engineering (LNEC).The structural safety control of dams is based on regular inspection and on the interpretation of data collected from the monitoring system, obtained from different measurement instruments installed according to the dam safety monitoring plan, and taking into account the results of numerical models, considering the material properties and the loads.Baixo Sabor dam, which is owned and was engineered and constructed by EDP-Energias de Portugal, is a good example of the technology and experience in the field of monitoring and instrumentation available in LNEC and in the Faculty of Engineering of the University of Porto (FEUP), able to analyze the behavior of the structure in all phases, namely during the first filling of the reservoir and exploitation period. Some results collected from different measurement instruments are presented, showing the proper functioning of the monitoring system.

To show how quality control of data, statistics, Machine Learning, and Artificial Intelligence will change Infrastructure Safety and Risk Management and Public Safety Forever is expected with the RESTATE project. This work aims to develop methodologies and procedures to support decision-making for the timely safety control of large infrastructures under operating conditions. This project aims to address new methodologies based on Deep Learning to create value in three main activities: quality control of monitoring data, analysis and interpretation of the structural behaviour, and safety assessment.

This paper presents the main characteristics of the automated monitoring system of Feiticeiro damand addresses a proposal for the definition of thresholds for the physical quantities measured throughthe use of an automated data acquisition systems (ADAS) for concrete dams.Feiticeiro is 45m high concrete gravity dam, designed, constructed and explored by EDP, located inPortugal in Sabor river (a tributary of Douro river).The defined thresholds for the physical quantities will be linked to an Internal Early Warning ControlSystem (IEWCS) of the dam, allowing the early identification and notification of potential abnormalsituations to the entities responsible for the dam safety.In operation since August 2016, the ADAS of the Feiticeiro dam defined by EDP allows themeasurement of several quantities used for the safety control, analysis and interpretation of the dambehaviour, such as: horizontal and vertical displacements, movements of joints, strain, uplift pressure,foundation displacements, seepage, concrete and air temperatures, and reservoir water level, amongothers.The measurements, obtained through the use of the ADAS developed and installed by ProintegaIngeneria, are sent to the gestBarragens system

The Fagilde dam is affected by concrete swelling reactions, of the ISR type, which induced serious damage in the dam

The concrete arch dam proposed for the 14th International Benchmark Workshop on Numerical Analysis (theme A) was numerically studied using computational codes purposely developed by the authors for dam analysis. Given that the codes use 2nd order 20-node brick elements, the concrete arch dam finite element mesh given as input by the organizing committee had to be adapted. The arch dam geometry follows closely the given input node coordinates. In order to ease the generation process, the foundation finite element mesh was totally redefined. The thermal analysis was done using a transient analysis model. A linear mechanical analysis including the gravity load, the hydrostatic pressure and the extreme temperature variations resulting from the thermal analysis was carried out. Then, a nonlinear model was considered at the dam/foundation interface in order to better simulate its behaviour, given that the arch dam is excavated into the rock where the support is made to act like a hinge. Finally, a nonlinear finite element analysis was carried out with a two scalar damage model at the brick finite elements representing the arch dam body. In this latter nonlinear analysis, a smeared reinforcement model was adopted at the upstream and downstream arch dam faces, following a linear elastic model. A discrete crack model was also analysed. Results of both thermal and mechanical analyses are presented and discussed.

Neste trabalho apresenta-se a aplicação de um modelo hidromecânico em pequenos deslocamentos desenvolvido para análise de fundações de barragens de betão. O modelo baseia-se numa formulação de elementos finitos de interface e requer um esquema de pré-processamento robusto, de modo a garantir que os contactos entre os diversos blocos que representam o maciço rochoso de fundação e a barragem são somente aresta/aresta. A parte mecânica do modelo permite uma representação rigorosa da distribuição de tensões ao longo das juntas, representadas por elementos de interface, e é perfeitamente compatível com a parte hidráulica. Apresentam-se os resultados da análise de estabilidade de um perfil gravidade sob ações estáticas e dinâmicas. Os resultados são comparados com os obtidos com um modelo em grandes deslocamentos. Conclui-se que é possível avaliar a segurança ao deslizamento de barragens gravidade recorrendo a modelos de interação em pequenos deslocamentos.

The safety control of large concrete dams, involving monitoring data and numerical modelling, is an important challenge being faced by all stakeholders involved in the exploration and safety of these structures with high social and economic value. In this context, the main concern is the detection of possible malfunctions as early as possible so as to ensure the real-time assessment of the structural behaviour under operation conditions. The structural response observed in large concrete dams is generated by the combination of the effects imposed mainly by the hydrostatic loading and by the temperature variations. Theassessment of the observed structural responses, like displacements, is usually performed through its comparison with values obtained by statistical models, also known as quantitative interpretation models, or by numerical models, composed of finite elements or other. The purpose of the research work presented herein is the development of a new methodology, coupled with a computational application, capable of properly assessing the structural behaviour of large concrete dams. This methodology is based on computing quantitative interpretation models and wavelet transforms from monitoring data obtained on site and in relating this type of information, extracted from variables related to the actions

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