Publications

The uplift pressures change the stress state of the rock mass foundation in a coupled hydromechanical process and may compromise the dam stability. Consequently, dam safety regulations specify the maximum values of the hydraulic conductivity and uplift pressures that can usually only be fulfilled after the execution of seepage and uplift control measures. The design of waterproofing and drainage systems is still based on an equivalent continuum approach, even though rock mass foundations are discontinuous media. The analysis of the piezometric monitoring data of several Portuguese large concrete dam foundations reveals that uplift pressures are site-specific and may even vary considerably across a given site, which can be critical for the safety assessment. From the data gathered in several dams, a probabilistic model that can be seen as an a priori prediction model for uplift pressures is proposed. Considering the difficulty in classifying the geologic foundation conditions beneath each piezometer in existing dams, it is assumed that the data come from a mixture of two beta distributions, representing foundations with regular and unfavorable geologic conditions. This model is a significant improvement over available approaches and will be instrumental for the assessment of existing dams and the design of new dams.

The characterization of the dynamic behavior of an arch dam, and its evolutionthroughout the structure's lifetime, provides important data for the safetycontrol process. Forced vibration tests remain a reliable technique for this purpose.The Baixo Sabor dam is a 123 m high arch dam recently built in Portugal.Forced vibration tests were performed before and after the reservoir filling.Two techniques for forced vibration test are compared, discrete frequencyscanning, the standard methodology, and continuous frequency scanning (sinesweep), a new proposed methodology, which allowed faster results withoutloss of precision. For the interpretation of test results two numerical models ofthe dam-reservoir-foundation system were built, and calibrated with the experimentaldata. A good match of numerical and experimental results wasobtained for the six lowest frequencies and corresponding mode shapes.

This study proposes an alternative approach to modeling the failure mechanisms of brickwork assemblages under combined shear

The Western Anatolia Region of Turkey is an important region of high seismic activity.The active dynamics of the region are shaped by a compression and expansion mechanism. This activemechanism is still ongoing and causes strong seismic activity in the region. The Frontinus Gate is amonument in the Roman city of Hierapolis of Phrygia located in southwestern Anatolia. The aim ofthis study is to investigate the seismic behavior of this stone masonry structure using discrete elementmodeling. For this purpose, nonlinear dynamic analyses were performed to simulate the structuralresponse of the gate under seismic excitation. Deformation, damage, and failure patterns induced inthe masonry gate for di erent levels of seismic action are evaluated and discussed. An earthquakewith a return period of 475 years is expected to cause some damage, but no collapse, while for areturn period of 2475 years, the models indicate collapse of the monument.

In this paper three historical masonry minarets in Istanbul, Turkey, are assessed for thedependency between the input harmonic motion and structural response parameters. Theirheights are 40, 73 and 74 m, while the slenderness is 12, 6 and 12, respectively. The discreteelement method is used in dynamic nonlinear analyses. Models were calibrated withmeasured natural frequencies. A series of sine-wave excitations is created for different frequency-amplitude pairs varying between 0.4 and 10 Hz, and between 0.1 and 1 m/s. Fromthe results of dynamic simulations, a general trend was observed for masonry minarets.Especially, slenderness and wall thickness play an important role on their dynamic responseand damage pattern. Dynamic behavior of these minarets cannot reliably be estimated bystatic non-linear analysis. Two engineering demand parameters (EDPs) are defined to characterizethe displacement of the minaret top and the inter-ring shear displacements alongthe minaret body. Damage performance criteria for minarets are proposed based on fourdamage states and tentative limit values are given. We were able to identify the occurrenceof those limit states as a function of frequency and amplitude of sinusoidal input motion.

This study presents a numerical investigation on the fracture mechanism of tension stiffening phenomenon in reinforced concrete members. A novel approach using the discrete element method (DEM) is proposed, where three-dimensional randomly generated distinct polyhedral blocks are used, representing concrete and one-dimensional truss elements are utilized, representing steel reinforcements. Thus, an explicit representation of reinforced concrete members is achieved, and the mechanical behavior of the system is solved by integrating the equations of motion for each block using the central difference algorithm. The inter-block interactions are taken into consideration at each contact point with springs and cohesive frictionalelements. Once the applied modeling strategy is validated, based on previously published experimental findings, a sensitivity analysis is performed for bond stiffness, cohesion strength, and the number of truss elements. Hence, valuable inferences are made regarding discontinuum analysis of reinforced concrete members, including concrete

Nowadays, the management and safety control of large dams is generally based on automatic monitoring, including the socalledseismic and structural health monitoring systems (SSHM), using the latest technology for automatic data measurement,acquisition and transmission. These systems should include software for automatic management and analysis of continuousmonitoring data and software for numerical simulation of the dam dynamic behavior using 3D finite element models. Thissoftware should be designed to provide useful and reliable information to meet the needs and expectations of stakeholders,and to support the studies of researchers and engineers responsible for structural health monitoring. This paper is focusedon the experience gathered from the SSHM system of Cabril dam, a 132 m high-arch dam, in Portugal, that has been undercontinuous dynamic monitoring since 2008. The importance of the software specifically developed for automatic modalidentification, automatic detection of seismic vibrations (distinct from vibrations due to the operation of discharge gates andpower groups), and automatic comparison between experimental data and computed results from a reference finite elementmodel of the dam-reservoir-foundation system, is highlighted. This software includes: (1) the generation of graphics withthe evolution of the identified natural frequencies over time and the comparison with calculated frequencies using differenthypothesis for concrete damage evolution; and (2) a service to automatically send emails summarizing key dynamic monitoringresults to stakeholders to provide the necessary support for informed management and engineering decision making.The main results from SSHM of Cabril dam are presented, namely regarding the evolution of modal parameter over time,considering the influence of water level variations, and the measured response during an earthquake event.

In this study, a novel computational modeling strategy is proposed to estimate the lateral load capacity andbehavior of unreinforced masonry (URM) structures. All commonly noted failure mechanisms are captured viathe proposed modeling strategy using the discrete element method (DEM) in three-dimensions (3D). Masonrywalls are represented as a system of elastic discrete blocks, where the nodal velocities are evaluated by integrating the equations of motion using the central difference method. Then, the mechanical interactions among adjacent blocks are examined utilizing the relative contact displacements and employed in the contact stress calculation. Through this research, a new stress-displacement contact constitutive model is considered and implemented in the commercial software 3DEC, which includes softening stress-displacement behavior for tension, shear, and compression along with the fracture energy concept. The results of the discontinuum models are validated on small- and large-scale experimental studies available in the literature with good agreement. Furthermore, important inferences are made regarding the effect of block size, the number of contact points, and contact stiffness values for robust and accurate simulations of masonry walls.

De acordo com a legislação portuguesa e tendo em consideração o risco sísmico da zona de construção das barragens é obrigatório a implementação de um Sistema de Observação Sísmica (SOS), incorporando instrumentação para caracterizar a ação sísmica induzida nas obras e a respetiva resposta estrutural. Em complemento, têm sido instalados Sistema de Monitoramento Dinâmico Contínuo (SMDC). O SOS permite não apenas a caracterização da ação sísmica, mas também a sua propagação ao longo do maciço rochoso, bem como a resposta estrutural da barragem. O SMDC visa identificar as características dinâmicas da barragem e sua evolução ao longo do tempo, considerando a variação das condições ambientais e operacionais, bem como a possível evolução das propriedades mecânicas dos materiais. Os processamentos são efetuados automaticamente incluindo a caracterização do nível de aceleração e a identificação dos parâmetros modais da barragem. Os valores obtidos pelo processamento automático são armazenados em base de dados, sendo enviados alertas quando são atingidos os patamares de alarme previamente definidos.Os resultados provenientes destes sistemas são comparados com os resultados de modelos numéricos sofisticados, calibrados com o recurso a ensaios experimentais de caraterização dinâmica realizados na obra durante a fase de primeiro enchimento.A combinação da monitorização dinâmica com os modelos numéricos é uma ferramenta fundamental no controlo de segurança estrutural e gestão de risco das barragens.

Today, there are several computational models to predict the mechanical behaviour of masonry structures subjected to external loading. Such models require the input of material parameters to describe the mechanical behaviour and strength of masonry constructions. Although such masonry materialparameters are characterised by stochastic

Os modelos detalhados de partículas, MP, ao terem em consideração a estrutura granular da rocha incluem de forma explícita a aleatoriedade do material e introduzem um tamanho limite à localização do dano. Neste trabalho é apresentado um modelo de partículas rígidas esféricas que tem sido desenvolvido tendo em vista o estudo da fratura em betão e em rocha. A interação entre partículas é definida com base na estrutura de Voronois dos centros de gravidade das partículas esféricas. Adota-se um modelo de contacto múltiplo, no qual a área da superfície de contacto é dada pela área da faceta comum dos Voronois associados a cada partícula. Vários estudos paramétricos são apresentados de modo a demonstrar a influência dos parâmetros micromecânicos, elásticos e resistentes, na resposta macroscópica dos sistemas de partículas.

This paper presents the results of in situ stress measurements and the application of a global interpretation model for evaluation of the most likely in situ stress field in the rock mass of the underground powerhouse cavern of the Salamonde II re-powering scheme, located in a mountainous zone of the North of Portugal. The objective of the study was to obtain the stress field prior to the powerhouse cavern excavation, for design purposes. Overcoring tests were performed in boreholes, before construction started. During early construction stages, when direct access to the vicinity of the cavern was created, flat jack tests were performed. For estimating the most likely state of stress in the rock mass, a global inverse analysis was carried out, which combined the overcoring and the flat jack tests results, using an appropriate methodology and a three dimensional numerical model. In order to assess the influence of time dependent effects on the in situstresses, a viscoelastic gravitational analysis was also performed using the same numerical model. The resultsobtained are compared and discussed.

Neste trabalho apresenta-se um modelo interpretativo tridimensional, que permite estimar o estado de tensão mais provável num maciço rochoso, integrando os resultados provenientes de ensaios de medição do estado de tensão in situ. Apresenta-se o caso de estudo da caverna da central subterrânea do reforço de potência do empreendimento hidroelétrico de Salamonde, localizado no rio Cávado, em Portugal. Neste caso de estudo, foiefetuada uma análise global integrando os resultados de dois tipos de ensaios, realizados em diferentes locais do maciço rochoso: i) ensaios de sobrecarotagem (STT), executados em furos de sondagens, antes de se iniciarem as obras do reforço de potência e; ii) ensaios de reposição de tensões com macacos planos (SFJ), realizados já em fase de execução da obra. Foi utilizado um modelo numérico tridimensional e uma metodologia apropriada, incluindo a geometria das escavações na altura da execução dos ensaios e a topografia do terreno, de forma a permitir uma estimativa do estado de tensão mais provável na zona da caverna da central.

Identification of potential failure mechanisms defined by the rock mass discontinuities or the concrete-rockinterface plays an important role in the safety assessment of concrete dam foundations. The paper presentsinstances of application of discrete elements deformable block models for analysis of these failure scenarios,representing the rock mass foundation and the concrete dam. The rock mass characterization needs and themethodologies for obtaining the input parameters for these models are discussed.

Os ensaios de macacos planos de grande área são utilizados para medir a deformabilidade de maciços rochosos e fornecem dados importantes para o projeto de grandes obras. Este ensaio consiste na abertura de um rasgo no maciço rochoso no qual é inserido um macaco plano de grande área. O macaco aplica pressão às paredes do rasgo através de óleo bombeado para o seu interior e são medidos os deslocamentos no maciço. A maior dificuldade na interpretação do ensaio reside no efeito provocado pela abertura de uma fenda de tração durante a aplicação de pressão pelo macaco plano. Para melhorar a compreensão sobre os efeitos da fenda de tração e assim melhorar a interpretação dos resultados do ensaio, desenvolveu-se um modelo numérico tridimensional do ensaio. O modelo permite estabelecer relações entre a tensão in situ perpendicular aos rasgos, a resistência à tração do maciço, as pressões aplicadas e a profundidade da fenda.

A methodology is proposed for dealing with the unbalanced stresses that arise from numerical models due to topography effects when horizontal stresses are applied at the vertical boundaries. The proposed methodology is used for understanding the role of topography on the distribution of in situ stresses due to both gravity and tectonic loadings. In particular, the influence of Poisson

Recent regulations introduced a limit state approach to geotechnical design by using representative values of the actions and of the strength parameters, partial safety factors that affect them, and by including safety margins in the calculation models. Moreover, Eurocode 7 stresses the importance of making use of test results for establishing ground parameters, and so rock joint shear tests are set to play a relevant role in the assessment of the shear strength required in the design of important projects, such as concrete dams, large bridge foundations, slopes, or underground excavations. In this keynote, joint shear tests are described, along with a presentation of their equipments and different procedures. Test results and calculations for the assessment of relevant shear strength parameters are illustrated, and several topics regarding sampling and variability are discussed. Opportunity is taken to present a practical apparatus allowing to perform simple shear tests (push tests) under very low normal stresses with advantages over tilt or pull tests.

The New Alto Ceira Dam is a 41 m high and 133 m long at the crest concrete arch dam, located in the middle zone of Portugal. The objective of the dam

Este documento descreve a rotura ocorrida na barragem indiana de Bhandardara,constituída por alvenaria, cujas causas estão relacionadas com problemas defissuração e acção da pressão da água no seu interior. O documento apresentatambém uma avaliação da segurança estrutural, com base em modelos numéricoselaborados através do Método dos Elementos Discretos, das obras de reabilitaçãopreconizadas que incluíram a utilização de ancoragens e pregagens.

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Masonry is a combination of units such as stones, bricks or blocks usually laid in a cementitious or limemortar. It is probably the oldest material used in construction and has proven to be both simple to buildand durable. Over the years, existing masonry constructions have inevitably suffered damage with time.Earthquakes, soil settlements, material degradation and lack of maintenance are the main reasons forthat. Careful and periodic assessment of such structures is necessary in order to evaluate their structuralcapacity and safety levels. However, performing the structural analysis of masonry construction is notan easy task. A review is presented of the main models based on the discrete element method and the available related numerical techniques that have been proposed for the analysis of masonry. The essential assumptions adopted by these models and numerical implementation issues are discussed. Differences between available models are illustrated by applications to various masonry problems including static and dynamic analysis of masonry arch bridges, walls, vaults, domes and ancient colonnades.This book is composed of 17 chapters authored/co-authored by 25 outstanding researchers from 11countries (Canada, France, Greece, Hungary, Iran,Italy, Mexico, Norway, Portugal, UK, USA), whichwere reviewed by 60 referees.

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This chapter consists of two parts. First a general overview is given: the exact definition of the Discrete Element Method is provided, and the main types of existing models are introduced; then the theoretical fundaments of the most important approaches available today for masonry analysis are given. The second part of the chapter focuses on 3DEC, the most widespread commercial DEM code for masonry analysis. This second part begins with a theoretical overview. Application issues for masonry structures are then considered (block material behaviour, contact representation, structural elements like cables or bars etc.). Among the practical examples arches, barrel vaults, walls, coloumns and complete structures (like houses) are presented, including the issues of quasi-static versus dynamic analysis and of block fracture as well. The readers can find helpful advice on how to simulate their own problems most effectively.

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Discrete element models have become a major tool for masonry analysis, allowing a suitable representation of its discontinuous nature and marked nonlinear behaviour. The chapter reviews the fundamental assumptions of the main DEM formulations available. It focuses more specifically on the widely used UDEC and 3DEC codes, explaining their relation with the other approaches, and the most relevant issues arising in their application to masonry. Applications to the main types of structures are reviewed, considering both static and dynamic analyses. Recent research providing comparisons of the numerical models with experimental and field data is particularly covered. The discussion of the different examples is aimed at clarifying the key capabilities of DEM and demonstrating the most effective ways of using it in a variety of masonry analysis situations.

This chapter is focused on the Portuguese experience on the developmentand exploration of systems for continuously monitoring dam vibrations, usingaccelerometers. The pioneer system for seismic and structural health monitoring(SSHM) installed in Cabril dam (the highest Portuguese arch dam: 132 m high) isdescribed in detail. The design of this system was the result of a long-term LNECresearch program, still ongoing. These monitoring systems should include softwaredeveloped to automatically perform the analysis of collected data, including theautomatic comparison with numerical results from 3DFE models. In view of thegood results obtained with the system in operation in Cabril dam since 2008, similarsystems have been installed in other large dams in Portugal, particularly in recentlybuilt dams. Finally, Baixo Sabor dam is presented as an example of a new Portuguesedam with a complete SSHM system, in operation since 2015. Themain experimentalresults obtained for both dams are shown, namely the evolution of natural frequenciesover time, mode shapes and the measured seismic response to earthquake events.

Para verificação do cumprimento das exigências de segurança das barragens,tanto relativamente à funcionalidade (cenários correntes), como em relação àsegurança ao colapso (cenários de rotura), é essencial utilizar modelos de simulação oude interpretação (no caso de obras existentes) do seu comportamento. Estes modelossão idealizações (simplificações) da realidade, tanto no que diz respeito às acções(modelos das acções), como no que respeita à componente estrutural (modelos estruturais).A solução destes modelos, através de adequados métodos de análise, quantificaparâmetros da resposta das estruturas que permitem avaliar a sua segurança, utilizandocritérios de segurança previamente definidos.A validação destes modelos pode ser feita, no caso de cenários correntes,através da sua comparação com os resultados da observação do comportamento debarragens. No caso de cenários de rotura, não existe muita experiência de comparaçãodestes resultados com situações reais: é pequeno o número de acidentes ocorrido e,mesmo nestes, o volume de informação é reduzido. Desta forma, o recurso a métodosexperimentais, para o estudo de cenários de rotura, tem uma importância acrescida.Assim o principal objectivo deste trabalho é contribuir para melhorar a capacidade deavaliação da segurança de barragens de betão envolvendo cenários de rotura pela fundação.Neste trabalho desenvolveram-se dois ensaios experimentais em modelosfísicos: um primeiro envolvendo uma barragem abóbada, para o estudo de cenários derotura da fundação para acções estáticas; e um segundo de uma barragem gravidadeensaiado em mesa sísmica, com vista a estudar a rotura pela fundação para acçõesdinâmicas.A previsão e interpretação dos ensaios foram efectuadas com modelosmatemáticos adequados, que permitiram a sua validação e posterior utilização no estudode outros cenários.

A brief description of the phenomena and problems associated with underground structures in hydraulic projects is presented, namely in what concerns the powerhouses, surge chambers and pressure tunnels and shafts. An analysis of the calculation methodologies followed in the structural design of this works is presented, as well as of the numerical models usually adopted, namely finite and boundary element models. Finally, some applications of computational mechanics are presented. First, a parameter study for underground powerhouses, with special emphasis in the definition of shapes, existence of several caverns,and in the tridimensional equilibria is described. Afterwards, examples of application to some hydraulic projects are illustrated: a large underground powerhouse in Mozambique, the Alto Lindoso hydroelectric power scheme in construction in the north of Portugal, and the Castelo do Bode tunnel, in operation, integrated in the water supply system to Lisbon.

O presente trabalho aborda a origem do estado de tensão interna dos maciços rochosos e apresenta os factores que o influenciam. Apresentam-se as técnicas e a aparelhagem correntemente utiiizada na determinação do estado de tensão, bem como a interpretação dos ensaios mais comuns, dando-se maior relevo aos ensaios com macacos planos pequenos (S F J) e com o extensómetro tridimensional (S T T),efectuados correntemente pelo LNEC.

Descreve-se sucintamente uma técnica para amostragem linear de descontinuidades em faces expostas de maciços rochosos e referem-se métodos para tratamento dos dados de campo com vista à definição defamílias de descontinuidades e caracterização de uma forma estatística da sua orientação, espaçamento e extensão. Apresentam-se os resultados obtidos para o caso de uma galeria subterrânea no aproveitamentohidroeléctrico do Alto Lindoso. Para as famílias de descontinuidade identificadas apresenta-se um estudo dos blocos tetraédricos que se poderão formar nas diferentes faces de rocha e analisam-se as suas condições de estabilidade.

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Apresentam-se, neste relatório, modelos numéricos baseados no método dos elementos da fronteira, desenvolvidos no LNEC para análise de estruturas subterrâneas. Tecem-se algumas considerações sobre o método dos elementos de fronteira, descrevem-se os modelos desenvolvidos para equilíbrios planos e tridimensionais e apresentam-se alguns exemplos de aplicação.

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This document presents a back analysis procedure for identification of the elastic parameters of transversely isotropic rock cores, containing an overcoring triaxial strain probe, from the strains measured during a biaxial test. A three-dimensional finite element model was developed to simulate the biaxial test on the overcored rock specimen and to compute the strains at the location of the strain gauges. Different optimisation algorithms were tested and the most suitable one was selected. The back analysis procedure was tested for identification of the five elastic parameters and the two orientation angles that characterise a transversely isotropic rock core. In spite that, with the developed methodology, convergence was reached and all those parameters could be identified, sensitivity analyses demonstrated that the results obtained were not stable and therefore they were not reliable. By introducing constrains based on common practice and previous experience, a stable and robust methodology was achieved: the three elastic parameters, E1, E2 and ?2, are reliably identified using the value of G2 calculated with Saint-Venant’s expression and a fixed value of ?1, while the orientation parameters are obtained from observation of overcored rock. Analysis of the results shows that application of this methodology represents an enormous step forward when compared with the traditional use of isotropy. Besides, the methodology is general and can also be used with other types of overcoring equipment. The five elastic parameters and the two orientation angles obtained can then be used, together with the overcoring strains, to compute the complete in situ state of stress.

This document presents the work developed by the PhD student Margarida Espada in the scope of the course unit Risk Analysis in Geotechnical Works of the Doctoral Program in Civil Engineering of the Faculty of Engineering of the University of Porto (FEUP). This work presents a reliability analysis, using the response surface method (RSM), for the case study of the left bank excavation slopes of the Baihetan arch dam foundation, which is one of the case studies of Margarida Espada's PhD thesis. The aim was to approximate an implicit limit state function by computing safety factors, using a discrete element model of the Baihetan left bank developed in 3DEC software, where the shear strength parameters of two important rock discontinuities were considered as random variables. The probability of failure was then obtained through an iterative process, using approximation methods. This work presents the 3DEC model developed to analyse the stability conditions in the Baihetan left bank and the results of the reliability analysis.

O problema da solução das equações de Navier Stokes é abordado neste trabalhopropondo-se uma técnica de representação das incógnitas deslocamentos e pressõesvariáveis no espaço e no tempo em série de Delta de Dirac e suas derivadas no tempocujos coeficientes se determinam com base na solução de sistemas de equaçõesdiferenciais definidos no espaço (problema com três variáveis espaciais independentesque pode ser estudado pelo método de Monge).

Neste relatório apresentam-se as equações básicas da elastodinâmica linear, as soluçõesfundamentais e o teorema da representação no domínio de tempo e de frequência.Para movimentos finitos de casca formula-se o teorema dos trabalhos virtuais e a suaimplementação pelo método dos elementos finitos.

Neste relatório apresentam-se os principais aspectos da modelação sísmica de barragensabóbada. Assim propõe-se: modelos numéricos de geração de sismos por uma falha; aforma como o sismo actua na barragem; modelos para estudar a influência da albufeirana vibração do conjunto; métodos para solução das equações do movimento; e novasformulações de elementos finitos para o problema estrutural.

In pressure tunnels and shafts, in addition to the mechanical effect that excavation has on the rock mass and the disturbance that it introduces in the water flow, also the contained water can interact from the mechanical and hydraulic points of view with the rock mass. Seepage in fractured rock masses is dominated by the flow that takes place through the joints, and this is highly d(;pendent on their properties, namely aperture and roughness. Joint aperture, in tum, i::; very sensitive to stress changes. Special attention must therefore be paid to the joints in hydromechanical analyses. In this report are presented some studies that were carried out for the hydromechanical characterization of joints of the Alto Lindoso rock mass and numerical simulations of the hydromechanical behaviour of two selected sections of the high pressure circuit.