Francesco Mugnai

3-D geomechanical rock mass characterization for the evaluation of rockslide susceptibility scenarios

An integrated methodology based on traditional field and remote surveys such as terrestrial laser scanning and terrestrial infrared thermography is proposed, with the aim of defining susceptibility scenarios connected to rock slopes affected by instability processes. The proposed methodology was applied to a rock slope threatening a coastal panoramic roadway located in western Elba Island (Livorno district, central Italy). The final aim of the methodology was to obtain an accurate three-dimensional rock mass characterization in order to detect the potentially more hazardous rock mass portions, calculate their volume, and collect all the required geomechanical and geometrical parameters to perform a detailed stability analysis. The proposed approach proved to be an effective tool in the field of engineering geology and emergency management, when it is often urgently necessary to minimize survey time when operating in dangerous environments and gather all the required information as fast as possible.

Correlation between erosion patterns and rockfall hazard susceptibility in hilltop fortifications by terrestrial laser scanning and diagnostic investigations

A holistic methodology combining conventional diagnostic investigations and kinematic analysis performed on 3D laser scanning survey is here proposed for rockfall hazard assessment and erosion patterns study, to map critical sectors and evaluate potential impacts on the conservation of cultural heritage sites built on unstable rock masses. Experiments carried out on the fortifications of Citadel, Gozo (Malta), led us to classify the susceptibility of the cliff surfaces to instability mechanisms, recognizing the wedge failure as the highest hazardous one. Observations on thin section of the rock textural properties and measurements of the resistance to abrasion completed the laser-based analysis, clarifying the intrinsic weakness of the outcropping limestones. Levels of conservation criticality were assigned to the rock mass sectors located underneath the historical buildings, and on site monitoring system was installed to follow the evolution of the crack patterns.

Microwave interferometric sensors as a tool for space and time analysis of active volcano deformations: The Stromboli case

A Ground Based SAR Interferometer (GB-InSAR) was installed at Stromboli volcano (Italy) in February 2003 to continuously monitor the behaviour of the morphological depression known as Sciara del Fuoco, SdF, with alerting purposes. This was decided as a consequence of the collapse of a large landslide from the NW slope of the SdF and the subsequent tsunami occurred on December 2002. The GB-In SAR system, working at Ku band, was set up on the stable right flank of the SdF; it has been continuously working and during this last five years has permitted to follow the temporal and spatial evolution of the mass movement in the SdF and the crater. Interferometric maps have permitted to assess the deformation field over a large portion of the target area and to characterize different processes. The system allowed to observe in particular two main events occurred on 5 April 2003 (a major explosion) and on 27 February 2007 (beginning of the effusive phase) respectively. The potential of the use of DInSAR from satellite platforms working at C band to understand the dynamic of the whole volcano has been also investigated. Different images acquired from the ERS2, RADARSAT and ENVISAT satellites before and after the 2003 collapse of the landslide, and before and after the 2007 event, have been interferometrically processed as well. Notwithstanding the restricted number of available images, the ground deformation occurred on the island due to the volcanic activity has been obtained with spatial and temporal characteristics complementary to those ones provided by GB-InSAR.

Monitoring and Modelling Slope Instability in Cultural Heritage Sites

The recent development of new remote sensing instrumentations, such as ground-based radar and terrestrial laser scanner, has encouraged the implementation of these non-invasive devices during diagnostic campaigns for the monitoring and geotechnical characterization of the instability processes in historic sites. This work presents the results of the research activities performed on the archaeological area of Roman Forum, Rome (Italy) and on the Citadel fortifications of Gozo (Malta). Ground-based radar demonstrated potentials for monitoring and surveillance at ‘single monument scale’, allowing real time warning in case of anomalies and deviations from the expected structural behaviour of the ancient masonry, thanks to the integration with the 3D model obtained from terrestrial laser scanning. On the other side, laser scanning provided fundamental base to calculate the probability of occurrence of instability mechanisms interesting, in the case study of Gozo, the Citadel rock mass, also providing a useful indication for the installation of on site monitoring network.

Sinkhole monitoring and early warning: an experimental application of ground-based interferometry

At Il Piano (Elba Island, Central Italy) 11 sinkhole events occurred on 9 different points on or close to a strategic road connecting Rio Marina to the rest of the island. In order to reduce the risk, a ground-based interferometric radar has been experimentally installed to detect possible precursor deformations of the ground. In this paper we present the results of a test simulating the occurrence of a sinkhole, which highlighted the criticalities of the method, and the successful prediction of a sinkhole event that could have endangered people travelling along the road. These experiences constitute a very important premise and confirm the possibility to measure precursor deformations even days before the opening of a sinkhole. This is due to the presence of a cover consisting in plastic material (clay, silt and even the street tar) that experiences a deformation before rupture as the sinkhole propagates from the bedrock.

Development of Nemo remotely operated underwater vehicle for the inspection of the Costa Concordia wreck

Remotely operated underwater vehicles are mobile robots increasingly used in underwater applications; these devices are widely used and suitable for different scenarios, for example, for patrolling and monitoring and also for underwater interventions. In the last 30 years, the remotely operated underwater vehicles have become more and more advanced; at the same rate with the progressive technological development of these vehicles, the market of the specialized component industry is fast-increasing. Generally speaking, a remotely operated underwater vehicle allows to investigate areas inaccessible or too dangerous for human beings. The use of remotely operated underwater vehicles during a mission, with the related implication of support ships and specialized pilots, or the involvement of professional divers, is usually associated with high costs. The reduction of these costs is an important topic in the underwater robotic field and the easy piloting of these mobile robots is a crucial aspect in their development. This article describes Nemo remotely operated underwater vehicle, a remotely operated underwater vehicle prototype specifically designed for the exploration of the Costa Concordia wreck, Isola del Giglio, Italy. Nemo remotely operated underwater vehicle can be considered a mini-remotely operated underwater vehicle, that is, a remotely operated underwater vehicle with weight less than 25 kg and easily deployable from a small boat. This article describes the main characteristics of the vehicle: the onboard control logic and on the development of a user-friendly graphical user interface for underwater navigation able to take advantage of its high maneuverability. It is worth to note that the developed graphical user interface enables to operate the vehicle even to inexperienced pilots. Preliminary experimental data collected during navigation are provided.

A method for locating rockfall impacts using signals recorded by a microseismic network

BackgroundRockfall events are one of the most dangerous phenomena that often cause several damages both to people and facilities. During recent years, the scientific community focused the attention at evaluating the effectiveness of seismological methods in monitoring these phenomena. In this work, we present a quick and practical method to locate the rebounds of some man-induced boulders falls from a landslides crown located in the Northern Apennines (Central Italy). The reconstruction of the trajectories was obtained by means of back analysis performed through a Matlab code that takes into account both the DEM (Digital Elevation Model) of the ground, the geotechnical-geophysical characteristics of the slope and the arrival times of the seismic signals generated by the rock impacts on the ground.ResultsThe localization results have been compared with GPS coordinates of the points and videos footage acquired during the simulations, in order to assess the reliability of the method. In most cases, the retrieved impact points match with the real trajectories, showing a high reliability. Furthermore, four different cases have been identified as a function of the geomechanical, geophysical and morphological conditions. Due to the latter ones, in some case it was necessary to assume different values for the propagation velocity of the elastic waves in the ground, here assumed to be isotropic and homogeneous.ConclusionsThis work aims at evaluating the effectiveness of a quick and practical method to locate rockfall events using a small-aperture seismic network. The obtained results indicate that the technique can provide quantitative information about the area most prone to impact of detached blocks. The method still presents some uncertainty, but reducing some of the approximations (e.g. by better constraining the velocity model), it could lead to prompt and more accurate results, easily applicable to hazard estimates.