The paper records the intensive monitoring programme planned to control the excavation effects and to ensure the long-term stability of the underground structures of Torrão hydroelectric scheme, including its neighbouring rock slopes. A preliminary analysis of the instrumentation data is reported. controI the structures. preliminary
On presente des details surl'auscultation des ouvrages souterrains et du massif rocheux encaissant du scheme hydroelectrique du Torrão. Des resultats preliminaires surle comportement des structures souterraines sont rapportes ici.
Einzelheiten ueber die Beobachtung der Untertagebauten der ?asserkraft anlage Torrão, und des sie umschlieBenden Felsens, werden vorgestellt. Es wird ueber vorlaufiqe, das Verhalten der Untertagebauten. betreffende Ergebnisse berichtet.
The hydroelectric scheme of Torrão,located on the river Tamega, a tributary of the Douro,. is one.of the most important hydroelec tric developments under construction in Portugal for the last years. The first controlled filling of the reservoir has taken place this very year.
A 69 m high gravity dam and an underground power plant, where two reversible-type 79MW peak load units are installed in two twin shafts, are the most important features of this scheme. The 60 m high shafts with a 17 m diameter cross section each are excavated in the left bank of the river, very close to the granitic slope of the Tamega valley, about 150 m away from the dam (Figure 1).
The hydraulic circuit is composed, besides the water intake and outlet, by a 12 m × x 9 m elliotical gate shaft and two inde - pendent tunnels of 6,70 m diameter, about 200 meters long.
The paper records the monitoring plan carried out to control the excavation effects and to ensure the long-term stability of the underground structures of Torrão hy droelectric scheme. An investigation of the rock mass properties as well as the more significant results about the structural behaviour of the underground openings and slope stability in the neighbourhood of the power station, are reported.
The monitoring plan of the underground openings was included in a more general do cument about the surveying of the Torrão hydroelectric scheme (LNEC, 1985). The plan was conceived bearing in mind the specific conditions of the different structures com posing the underground complex and namely, the location of the two-shaft power plant, very close to the abrupt slope of the granitic left bank of the river.
With such olan it was intended to record an amount of significant data, to make it possible the appraisal of the punctual and general safety, either during construction or during initial and continuing exploitation. It was also intended to make the best use of such data during construction, in order to optimize the construction tech niques and the final design.
So, priority was given to the determination of parameters which, in a simple and direct way, would express the structural behaviour and allow, by their greatness and time evolution, the interpretation of such behaviour.
