Monica Ghirotti

San Leo: Centuries of Coexistence with Landslides

The ancient fortified city of San Leo is built on a limestone plateau. The rock slab is tectonized and crossed by several families of joints and faults, while the underlying foundation of the rocky cliff is composed of gentle clay slopes, modelled in the so-called “Argille Scagliose” geological units. The differential weathering of the upper rock formation with respect to the ductile clays has produced ledges and overhangs on the cliff face. Furthermore, weathering and/or movement of the underlying clays has caused the opening and widening of vertical fractures in the brittle limestone rock masses, diffused over the entire rock mass. The evolution of plastic movements (slides and flows) in the underlying clay units might undermine the limestone slab and endanger the stability of the rocky cliff, thus posing risk to the fortified city of San Leo and its notable cultural heritage. In this paper, historical and recent slope instability events are described, on the basis of historical documents and modern investigations.

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.