Engineering geological characterization and comparison of predicted and measured deformations of a cavern in the Italian Alps

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.