Design and construction of the Timpagrande powerhouse

The Timpagrande underground powerhouse, built between 1977 and 1978, was excavated in a highly fractured granite formation having poor mechanical properties. In this paper a description is given of the in situ and laboratory tests performed to characterize the rock mass, of the criteria adopted during the design stage to define the relevant geotechnical parameters, of the methods used for the construction and of the system adopted to monitor the real behaviour of the structure. Finally, the results of a back analysis are presented, which attempt to identify the real values of the geotechnical parameters of the rock mass on the basis of the control readings.