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).

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