Event scenario analysis for the design of rockslide countermeasures

The Torgiovannetto quarry (Assisi municipality, central Italy) is an example of a site where the natural equilibrium was altered by human activity, causing current slope instability phenomena which threaten two roadways important for the local transportation. The quarry front, having a height of about 140 m, is affected by a 182,000 m3 rockslide developed in intensely fractured limestone and is too large to be stabilized. In 2003 some tension cracks were detected in the vegetated area above the quarry upper sector. From then on, several monitoring campaigns were carried out by means of different instrumentations (topographic total station, extensometers, inclinometers, ground-based interferometric radar, laser scanner and infrared thermal camera), allowing researchers to accurately define the landslide area and volume. The latter’s major displacements are localized in the eastern sector. The deformational field appears to be related to the seasonal rainfall. The landslide hazard associated with the worst case scenario was evaluated in terms of magnitude, intensity and triggering mechanism. For the definition of the possible runout process the DAN 3D code was employed. The simulation results were used in order to design and construct a retaining embankment. Furthermore, in order to preserve both the safety of the personnel involved in its realization and of the roadways users, an early warning system was implemented. The early warning system is based on daily-averaged displacement velocity thresholds. The alarm level is reached if the prediction based on the methods of Saito (1969) and Fukuzono (1985) forecasts an imminent rupture.