Engineering geological characterization and comparison of predicted and measured deformations of a cavern in the Italian Alps Michele Sapigni a , Giovanni La Barbera b , Monica Ghirotti c, * a Enelpower S.p.A., Venezia, Italy b Enel.Hydro S.p.A., Rome, Italy c Dipartimento di Scienze della Terra e Geologico-Ambientali, Alma Mater University of Bologna, Via Zamboni 67, 40127 Bologna, Italy Received 29 May 2002; accepted 25 October 2002 Abstract A detailed engineering geological characterization and performance monitoring were carried out at the site of an underground powerhouse cavern in the Italian Alps. In the area of the hydroelectric project, consisting of a 4-m diameter and 10-km-long diversion tunnel and a powerhouse cavern (20 m wide, 39 m long and 30 m high), metamorphic anisotropic rocks, are present. A pervasive foliation, whose trend describes an open fold at the cavern site, characterizes the geological structure. The studies include petrographic analyses and geo-mechanical properties of the rocks, in situ stress measurements and rock- mass classifications for the cavern site as well as the surrounding area. Based on field investigations, two numerical models (FEM and DEM codes) were used to investigate the overall stability of the excavation and to predict the expected deformation caused by each excavation phase. The measurements of actual deformations, by multi-base extensometer data, are reasonably close to those predicted through the numerical approaches. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Cavern; Geological observations; Monitoring; Numerical modelling; Italian Alps 1. Introduction The empirical rock-mass classification systems commonly used to design excavations in rock have long been recognised as useful tools for the prediction of rock masses and choice of support requirements on the basis of experience in similar geologic conditions (Grimstad and Barton, 1993; Barton et al., 1974). Rock-mass properties derived from these empirical systems are commonly used, in a preliminary phase, as data input for modelling the rock-mass behaviour around an excavation. Numerical models can be used to compute the redistributed stress field around the excavation, to examine the mechanical response of a jointed rock mass around an unsupported or supported tunnel and to predict the expected deformation caused by each excavation phase (Bhasin et al., 1995, 1996; Bhasin and Høeg, 1998; Chryssanthakis et al., 1997; Pelizza et al., 2000). Numerical models simulate the response of discontinuous media involved in tunnel- ling, but their results are strongly influenced both by the selection of rock and rock joint input parameters and by the joint constitutive models (Cundall and 0013-7952/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0013-7952(02)00247-8 * Corresponding author. Tel.: +39-51-2094534; fax: +39-51- 2094522. E-mail address: ghirotti@geomin.unibo.it (M. Ghirotti). www.elsevier.com/locate/enggeo Engineering Geology 69 (2003) 47 – 62