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ABSTRACT: After calling the attention to the importance of the hydromechanical interaction in pressure tunnels and shafts, the paper describes briefly a finite element numerical model of the hydromechanical behaviour of fractured rock masses. The mechanical and hydraulic behaviours are modelled separately, and the hydromechanical coupling is obtained using an iterative procedure. Both the mechanical and the hydraulic models are suitable for quasi-plane analyses of multilaminated media and can include discrete joints. In order to enhance the importance of hydromechanical coupled analyses for a correct understanding of the behaviour of pressure tunnels and shafts two parametric studies of a pervious thick walled cylinder and of a concrete lined pressure tunnel with an initial gap between the lining and the rock mass are then presented. RESUME: Après avoir montre l'importance de I'interaction hydromecanique en tunnels et puits sous pression, on fait une bref description d'un modèle numerique en elements finis du comportement hydromecanique des massifs rocheux fractures. Les comportements mecanique et hydrauliques sont modelises separement et le couplage hydromecanique est obtenu par une procedure iterative. Les modèles mecanique et hydraulique sont tous les deux souhaitables pour des analyses quasi-planes des milieux multilamines et peuvent inclure des joints isoles. Sont finalement presentes deux etudes parametriques qui montrent l'importance des analyses hydromecaniques couples, pour une bonne comprehension du comportement des tunnels et des puits sous pression. ZUSAMMENFASSUNG: Nachdem auf die wichtigkeit der hydromechanischen Interaktion aufmerksam gemacht wurde, beschreibt diese Arbeit kurz ein numerisches Modell finiter Elemente des hydromechanischen Verhaltens von geklueftetem Fels. Das mechanische und das hydraulische Verhalten werden in getrennten Modellen dargestellt; die hydromechanische Kopplung wird durch ein Iterativverfahren erhalten. Sowohl das mechanische als auch das hydraulische Modell sind fur "quasi-plane" Analysen von vielschichtigen Medien geeignet, und können isolierte Kluefte mit einschlieβen. Um die Bedeutung von hydromechanischen Analysen fuer ein korrektes verstandnis des Verhaltens von Druckstollen und Druckschachten hervorzuheben, werden zwei Parameter-Studien, eines dickwandigen durchlassigen Rohres und eines mit Beton ausgekleideten Druckstollen mit einer urspruenglichen Spalte zwischen Beton und Fels, vorgestellt. 1. INTRODUCTION: Unlined and concrete lined pressure tunnels and shafts are typical kinds of underground openings where the interaction between mechanical and hydraulic problems must be considered for an adequate design and safety evaluation. The existence of this interaction makes it important to study them as an integrated process, i.e., in a coupled way. The hydromechanical behaviour of fractured rock masses is influenced in a decisive way by the presence of joints. They are responsible in a large extent for the seepage which occurs through the rock mass, and are also the most sensitive elements of the rock mass with respect to deformation under stress changes. As water flow through a joint is highly dependent on its characteristics, namely aperture, which is very influenced by the state of stress, hydromechanical studies of fractured rock masses must pay special attention to the role of joints and to a correct assessment of their properties. In the particular case of pressure tunnels and shafts, the importance of the hydromechanical interaction is influenced by the type of lining that is used. In the case of steel linings, this problem is not relevant, since the flow of water from or into the rock mass does not take place. However, this is an expensive solution and nowadays, owing to the progresses made in understanding the behaviour of the composite structure formed by the rock mass and the lining, in the techniques of rock mass improvement and in the use of pre-stress in concrete linings, the use of steel lining is usually restricted to zones where the rock mass properties.
Rock Mass Foundation Deterioration of Portuguese Concrete Dams: The Varosa And Venda Nova Case Histories
Pedro, J.O. (LNEC - Laboratorio Nacional de Engenharia Civil, Lisbon) | Mascarenhas, A.T. (LNEC - Laboratorio Nacional de Engenharia Civil, Lisbon) | Sousa, L.R. (LNEC - Laboratorio Nacional de Engenharia Civil, Lisbon) | Rodrigues, L.F. (LNEC - Laboratorio Nacional de Engenharia Civil, Lisbon) | Silva, H.S. (LNEC - Laboratorio Nacional de Engenharia Civil, Lisbon) | Castro, A.T. (LNEC - Laboratorio Nacional de Engenharia Civil, Lisbon)
ABSTRACT: This paper reports the case histories of foundation deterioration in the Portuguese Varosa and Venda Nova arch dams. The main characteristics of the works, the geological conditions, the observation systems, the detection of the abnormal behaviours, and aspects of the repair works are referred to. RÉSUMÉ: Ce travail presente les cas de deterioration de fondation dans les barrages-vôûte portugaises de Yarosa et Venda Nova. Les caracteristiques principales des ouvrages, les conditions geologiques, les systèmes d'observation, la detection des comportements anormaux et des aspects des travaux de reparation sont cites. ZUSAMMENFASSUNG: Dies Referat stellt die Pallstudien des Felsgruendungsverfalls in den portugiesischen Varosa und Venda Nova Bogenstaudammen vor. Die Hauptmerkmale der Bauten, die geologischen Beschaffenheiten, die Beobachtungssysteme, die Entdeckung der ungewöhnlichen Verhalten und Eigenarten der Reparaturarbeiten werden besprochen. 1 INTRODUCTION: Seepage through the rock mass foundation of concrete dams is of major importance to the uplift set up, velocity and the corresponding rates. Uplift in the foundation is one of the main actions on those structures, due to its permanence along the life time and to the forces it originates, which may condition the stability of the structure. Seepage velocities in the discontinuities of the foundation may give rise to erosive actions, or else they may produce deposition of materials and so contribute to changes in the hydraulic and mechanical characteristics of the medium. Physical-chemical actions also occur, which are related to the rock mass properties and of treatment works. These actions may alter hydraulic and mechanical properties of the rock mass during the exploration. Seepage control is achieved by means of the foundation water tightening and drainage works. These make it possible a limitation of uplift and see page velocities, avoiding excessive gradients, and preventing the occurrence of excessive flow. Though in the last years there has been significant progress in the hydraulic characterization of rock mass, the hydraulic conductivity of rock media still has to overcome some difficulties (Mascarenhas 1979). In addition to the anisotropic and heterogeneous characteristics of the permeability, account should be taken of its variation with the state of stress. This is particularly important in the case of fissured media. The variation of the permeability with the state of stress, particularly when this results from failures affecting the grout curtain and the drainage system, may be associated with a marked decrease of the efficiency of the works (expressed by increase of uplift at the level of the drainage curtain and of drainage seepage). This phenomena frequently detected during the first filling has been observed in numerous arch dams. There is also evidence of reduced efficiency of those works when they are located in highly compressed zones of the rock mass. In this case a marked decrease of permeability is expressed by a decrease in the drainage capacity. The cases of Varosa and Venda Nova arch dams (Portugal) are examples of deteriorations in water tightening and drainage systems which evidence the need of more adequate studies on the hydromechanical behaviour of foundations. 2 ROCK MASS FOUNDATION DETERIORATION: 2.1 General Deterioration of dams (accidents and incidents) is usually concerned with the dam body and its foundation, appurtenant works, and slopes downstream of the dam and of reservoirs. In the present paper, we are mainly concerned with deterioration occurring in the rock mass foundation of concrete dams, though the behaviour of whole dam-foundation complex has to be taken into account. Concrete dams have different structural types, each one demanding the contribution of the rock mass foundation in a specific way.
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics (0.89)
- Management > Professionalism, Training, and Education > Communities of practice (0.61)
- Data Science & Engineering Analytics > Information Management and Systems > Knowledge management (0.61)
Applications of Computational Mechanics to Underground Hydroelectric Schemes
Sousa, L.R. (LNEC - Laboratorio Nacional de Engenharia Civil, Lisbon) | Lamas, L.N. (LNEC - Laboratorio Nacional de Engenharia Civil, Lisbon) | Almeida E Sousa, J. (FCTUC - Faculdade de Ciencias e Tecnologia, University of Coimbra)
ABSTRACT: An analysis of the calculation methodologies followed in the structural design of underground structures in hydroelectric projects is presented, as well as the numerical models usually adopted. Some applications of computational mechanics to the Alto Lindoso hydroelectric power scheme, in Portugal, are presented. Numerical models were developed for the underground powerhouse complex and for the surge chamber. A comparison between the predicted values from the numerical solutions is made in order to permit a continuous safety evaluation of the underground structures. RÉSUMÉ: Une analyse des methodes de calcul utilisees dans la conception structurale des structures souterraines dans des projets hydro-electriques est presentee, ainsi que des modeles numeriques habituellement adoptes. Quelques applications de la mecanique computationnelle au projet hydro-electrique du Alto Lindoso, au Portugal, sont presentees. II a ete developpe des modèles numeriques pour le complexe de la usine souterraine et pour la cheminee d'equilibre. La comparaison entre les valeurs prevues pour les solutions numeriques est effectuee à fin de permettre une evaluation de securite continue des structures souterraines. ZUSAMMENFASSUNG: Es werden die Berechnungsverfahren, die zur Erstellung des strukturellen Entwurfs von unterirdischen Strukturen bei hydroelektrischen Projekten verwendet werden, dargestellt, sowie die numerischen Modelle, die dabei gewöhnlich verwendet werden. Im folgenden werden einige Anwendungen von Computermechanik im Bezug auf das hydroelektrische Kraftwerk in Alto Lindoso/Portugal erlautert. Zur Analyse der verschiedenen Bauphasen wurden numerische Modelle fuer das unterirdische Kraftwerkshaus und das Wasserschloβ entwickelt. Um eine kontinuierliche Bewertung der Sicherheit der unterirdischen Strukturen zu erhalten, werden die tatsachlichen Werte mit denen, die von den numerischen Lösungen vorausgesagt wurden, verglichen. 1 INTRODUCTION Considerations are made about the conception and calculation methodologies followed in the structural design of underground structures in hydroelectric projects, as well as about the computational methods usually adopted for predicting the structural behaviour and quantifying actions. Some applications of computational mechanics to the Alto Lindoso hydroelectric power scheme, in Portugal, are presented. Special emphasis is made to a 3-D finite element numerical system suitable for the analysis of underground structures. The numerical models were developed for the underground powerhouse complex and for the surge chamber for the analysis of the different construction sequences. A comparison between observed and predicted values from numerical solutions is made in order to permit a continuous safety evaluation of the underground structures. Also a 3-D boundary element model was used in the determination of the most probable in situ state of stress in the rock mass. 2 CONCEPTION AND CALCULATION OF UNDERGROUND STRUCTURES 2.1 Preliminary considerations The use of the underground space for hydroelectric power schemes has been widely implemented where adequate conditions exist, because of the advantages that it brings when compared with surface solutions. The costs with the excavations and supports are usually balanced with the costs of the foundation and superstructure of surface powerhouses. In good rock masses, the supports of the tunnels, caverns and shafts can be considerably reduced or even eliminated, which can result in more economical solutions. Furthermore, the expropriation costs are reduced, and smaller economical and environmental impacts are originated. On the other hand, significant advances in underground technology and in computational methods have allowed an increasingly rational approach to the design of these underground structures. In these projects, several types of underground openings exist: the powerhouse complex, high and low pressure tunnels and shafts, surge chambers, and adits. Several possible types of arrangements exist for the hydraulic circuit. A very good example of the complexity of these projects is given by the Alto Lindoso power scheme, in the north of Portugal (Figure 1).
- Energy > Renewable > Hydroelectric (1.00)
- Energy > Power Industry (1.00)
Geotechnical Investigations And Monitoring Plan For the Power Increase of the Miranda Hydroelectric Project In Portugal
Aguiar, A.A. (EDP - Electricidade de Portugal, Oporto) | Sousa, L.R. (LNEC - Laboratorio Nacional de Engenharia Civil, Lisbon) | Pinto, J.L. (LNEC - Laboratorio Nacional de Engenharia Civil, Lisbon)
ABSTRACT: The Miranda hydroelectric development is located in river Douro in Portugal. This development made It necessary to construct in a first phase, a massive-head buttress dam, three independent underground hydraulic circuits and an underground powerhouse. Recently, a decision was made to carry out works for the power increase of this hydroelectric power station. A monitoring plan was established for the new structures of the Miranda development, which implied also reactivation of some observations for the old power station. The observations established in the plan concern also the characterization of the deformability and strength of the rock mass and of the concrete of the supports, and in situ stress measurements. Some results referring to observations made during the beginning of construction are presented. RÉSUMÉ: Le projet hydroelectrique de Miranda est situe sur le fleuve Douro au Portugal. Ce projet a rendu necessalre la construction, dans une première phase, d'un barrage à contreforts de chute massive, trois circuits hydrauliques independants et une usine souterraine. Recemment, on a decide d'effectuer des travaux d'elargissement de l'usine. Un plan d'observation a ete etabli pour les nouvelles structures du projet de Miranda, ce qui a aussi comporte la reactivation de quelques observations pour I'usine ancienne. Les observations etablies dans le plan concernent la caracterisation de la deformation et de la contrainte du rocher et du beton des appuis, et la mesure contrainte in situ. On presente quelques resultats concernant les observations. ZUSAMMENFASSUNG: Das hydroelektrische Projekt von Miranda befindet sich am Fluβ Douro in Portugal. Dieses Vorhaben erforderte in einer ersten Phase den Bau eines massivkopfigen Stuetzdamms drei unabhangiger unterirdischer wasserkreislaufe und eines unterirdischen Maschinenhauses. Erst vor kurzem wurde die Entscheidung getroffen, das Kraftwerk zu vergröBern. Der Beobachtungsplan, der fuer die neuen Strukturen des Miranda-Projekts aufgestellt wurde, beinhaltete auch die Reaktivierung einiger Beobachtungen, die im Bezug auf das alte Kraftwerk gemacht wurden. Die im PIan aufgestellten Beobachtungen betreffen unter anderem die Charakterisierung von Verformbarkeit und Widerstand der Felsmasse und den Beton der Auskleidung, sowie Feldspannungsmessungen. Es werden auch einige Beobachtungen, die wahrend des Beginns der Bauarbeiten gemacht wurden, dargestellt. 1 INTRODUCTION The Miranda hydroelectric power scheme is located on the river Douro, in the northern border between Portugal and Spain (Figure 1). The Douro, one of the most Important rivers of the Iberian Peninsula, has a length of approximately 850km and a total catchment area of 97,000km. It is located in a site where the course of the river suddenly changes its direction, forming an elbow at an angle of 45°. The profile of the valley is shaped like a very open V the slope of the banks is not very pronounced. The nature of the ground on the site of Miranda plant is complex. It is a zone of general metamorphisms, the rock mass consists of rocks like micaschists, migmatic rocks and anatexy granites. During the initial exploitation phase, that started in 1961, a diamond-shaped massive head buttress dam was built, with maximum height above lowest foundation of 80m and a developed crest including the abutments of 263m. The spillway with four openings is located in the central zone of the dam. Three independent hydraulic circuits were formed for each set, comprising the intake, penstock, draft tube and tailrace tunnel (Figure 2). The powerhouse is a cavern with 80m long, 19.6m wide and 42.7m height of excavation with a horse shaped profile.
- Energy > Renewable > Hydroelectric (1.00)
- Energy > Power Industry (1.00)