A large pumped-storage power generating project with an underground power-house of unusual dimensions is under construction at Lago Delio for ENEL.
A system of geomechanical investigations has been provided for this project, and it makes the object of this paper. The geophysical tests and the determination of rock deformability by both the hydraulic pressure chamber and the jack methods are described; notice is given also of the tests on the state of natural stresses. The paper deals then with the equipment installed for measurement of the deformations in rock during excavation and a report is given of the results obtained during progress of the work.
ENEL (Italian Electric Energy Authority) have now under construction the underground powerhouse for the Lago Delio project, which is described in another paper presented in this same Congress[1]. The required excavation is about 21 m wide, 60 m deep and 192 m long.
The excavation is driven through a fine-grained paleozoic gneiss with sub-vertical foliation planes running almost perpendicular to the axis of the cavern. Besides, the rock is crossed by an intricate system of fractures and joints of different strikes, with local weathered zones.
Owing to the magnitude of the underground work and the complexity of the existing conditions, the surface geological surveys were integrated by exploratory core-drilling and tunneling as shown in fig. 1. These permitted to set up a system of geophysical and geomechanical tests (with the co-operation of Fondazione Lerici and Ismes respectively) from which a good aid was obtained for a better knowledge of the main characteristics of the rock in question.
In the area originally selected for construction of the powerhouse, a set of 32 boreholes were drilled (to a total length of 4000 m) along two alignments parallel to the powerhouse axis, to depths of 80 m and 120 to 150 m respectively. On these alignments, measurements of seismic velocity were taken for horizontal travels spaced every 10 m in depth. The seismic pulses obtained by exploding small shots inside special shot holes are received by geophones located inside receiver holes spaced some 40 m apart. The same receiver holes are used also for sonic logging to detect, meter by meter, the propagating velocity of sonic waves all around the hole in view to recognize the integrity of the rock. Details of the geophysical methods used are described in other papers [2] [3].
L’ENEL (Office National Italien de l’Energie Electrique) a en cours de réalisation le grand aménagement hydroélectrique à accumulation par pompage du Lac Delio avec une usine souterraine de dimensions exceptionnelles.
A cet effet, des recherches géomécaniques différentes, dont on fait mention dans le présent mémoire, ont été exécutées: plus précisement on cite les recherches géophysiques et les déterminations de la déformabilité de la roche effectuées par la méthode de la chambre hydraulique à pression et la méthode des vérins; on décrit aussi l’essai de l’état de contraintes naturelles. On illustre également les appareillages adoptés pour la mesure des déformations de la roche en phase d’excavation, en exposant les résultats obtenus au cours des travaux.
Die ENEL (Nationalanstalt för Energie) föhrt den Bau der grossen Erzeugungsund Pump-Wasserkraftanlage Lago Delio aus, die mit einer Maschinenkaverne ausserördentlicher Ausdehnung versehen ist.
Es wurde för diese Maschinenkaverne eine Reihe geomechanischer Untersuchungen vorgenommen, öber welche dieser Beitrag Bericht gibt Erwähnt wurden die geophysikalischen Untersuchungen und die Ergebnisse der Verformungsmessungen des Felsens − die durch die Methoden der Druck-Wasserkammer und der hydraulischen Winden durchgeföhrt wurden − und, nachher, den Versuch öber den Zustand der natörlichen Spannungen.
Es werden, daher, die för die Messung der Felsverformungen während des Aushubes installierten Einrichtungen beschrieben und die im Lauf der Arbeiten erreichten Ergebnisse aufgeföhrt.
