In Italy, during the last decade, several hydroelectric plants - particularly pumped storage plants - have been constructed by ENEL. Improvements made in the performance of in situ tests, in the use of numerical tools, in the design of monitoring systems and in construction technologies are reported.
Wahrend der letzten Jahrzehnten sind in Italien mehrere Wasserkraftwerke - besonders Pumpspeicherwerke - vom ENEL gebaut worden. Es wird hier ueber den Entwicklungen in der Ausfuhrung von in-situ Versuchen, in der Benutzung numerischer Rechenmethoden, im Entwurf von Überwachungsystemen und in den Bautechnologien berichtet. RESUME. In Italie, pendant la dernière decennie, ques, en particulier installations de pompage, ont ete construites par ENEL. On reporte ici les ameliorations faites dans l''execution methodes numeriques, le projet de systèmes de contrôle et les technologies de construction
In the sixties ENEL first tackled the design of pumped-storage power plants which reached the installed power of 1000 MW with 125 MW per unit. It became evident that the most suitable solution was to install huge underground groups (see Dolcetta 1971 a, 1971 b, 1972). On the one hand, this minimizes the inertia of the hydraulic system by shortening the length of pressure tunnels, and at the other it solves, in a satisfactory manner, all the problems related to the preservation of environment, and to the availability of areas. Besides, a clear financial advantage with respect to the out-door solution was achieved in most cases. However the required size of caverns turned out to be considerably bigger than that of previous Italian achievements. In fact the new powerhouses required an excavation volume of 250.000 m3, while in general those built previously didn''t reach 100.000 m each. Moreover the openings were of a remarkable height (about 60 m) since they had to house ternary units (alternator-turbine-right pump) and because of pumps cavitation problems (Fig.l). Later the introduction of new single or multi-stages reversible machines allowed to reduce the height of the main cavern to less than 40 m, and required some increment of its width. The construction of the pumped-storage stations made clear that the underground location might be the right solution also for other kinds of plants. Therefore this choice was made even in the case of plants for power production only, when the characteristics of the environment were difficult because of lack of building area and poor stability conditions of the site. Studies about possible underground installations of nuclear powerplants were also started. In view of such an amount of work from the outset a program was sketched out to improve the knowledge about the real behaviour of the rock mass. More advanced design criteria were established as soon as new information was available particularly from construction experience. The Geotechnical Service of ENEL Central Construction Direction has followed all the design and construction activities carried out by Peripheral Operational Centers, thus assuring the organization of the information in a comprehensive theoretical frame, and its prompt diffusion. During the last twenty years ENEL''s activities in the afore mentioned field stimulated a process which progressively updated and improved the rock mass behaviour models to be used in design. Their complexity, however, was made, each time, compatible with the available knowledge about the characteristic geotechnical parameters, and with the stage of their experimental determination. In the above mentioned process the monitoring of the excavation play a very important role. Besides its usefulness in the construction phase it represents the base for further evolution of the design itself, either with regard to the individuation, and better determination of characteristic geotechnical parameters, or with regard to adaptation of interpretative models. However it is important to stress (Martinetti, 1977) the difficulty of selecting reliable instruments and planning measurements in order to.assure regular surveys, even for critical situations as those of underground excavation stope. This implies the necessity of a certain redundancy in the monitoring system. In fact in the case of a first group of new underground powerhouses the loss of essential information about real behaviour of the excavation was avoided in spite of the ill-functioning of some instruments of the main monitoring system. It was indeed possible to rely on supplementary information provided by other equipment and measurement systems which were less sophisticated and less expensive FIG. 1 — S. Fiorano pumped storage power station View of the pump zone from the turbine level. ve, but much more positive and reliable. The wealth of information, gathered during the construction of the most important powerhouses listed in table 1, hasn''t been completely analyzed yet. Nevertheless advances in the knowledge of the rock mass behaviour and in the computer simulation capabilities suggest the possibility that a new back-analysis programme, worked out also on the base of a first attempt (Martinetti, 1977), could give additional important explanations and ideas.