A team of researchers from different Universities and Public Institutions from Italy and USA, of which the proposing of this project is the Italian coordinator, has been mobilized to investigate geotechnical and geological aspects of the destructive earthquake sequence that occurred in Central Italy from August to October 2016. During the reconnaissance activities following the seismic events, many information have been gathered and systematically collected and many instability phenomena have been documented, that can be used to advance our understanding of landslides-triggered earthquakes. The data collection have been performed using traditional mapping/observational methods and advanced imaging tools. Preliminary field investigations have been focused, among others, on major rockfalls and rockslides, including a large slide that dammed a river, as they could threaten road infrastructures.
Based on this preliminary field work, in this research project we want to investigate major rock slope failures occurred at three selected sites during the Central Italy earthquake sequence. These case-studies will be back analysed to investigate influence of rock mass behaviour and slope morphology on the instability mechanism under dynamic loading. Analyses will rely on a thorough review of existing geological and geotechnical data, specific field and laboratory investigations and analysis of strong motion data. Results are expected to provide insight on the factors that control occurrence of slope instability and type of failure mechanisms under dynamic loading due to medium-high seismic events, typical of many regions of Italy and other regions in the world.
The findings of the study may have important engineering implications in that they can increase our capability to mitigate seismic risks in inhabited mountain areas related to earthquake-triggered landslide hazard.
In the last decade, there has been a growing international literature on seismically-triggered rockfalls and rockslides, even if published data mostly refer to very large earthquakes or analyses of events induced by historical earthquakes. These data confirm the important role played by slope geometry and strong ground motion intensity (estimated through PGA) as ¿predisposing factors¿ (Faccioli, 1995) to explain seismic landslide distribution.
On the other hand limited data is available for medium-high magnitude events, such those that hit Central Italy during the recent 2016 seismic sequence. The number and significance of landslides triggered by these earthquakes represent an unprecedented and extremely valuable wealth of data. These data span from small-size to large-volume slope failures, encompassing different geological formations such as limestones and sandstone-marl alternations. In this research project, we propose to investigate in detail three selected case-histories of rockfalls and rockslides occurred during the Central Italy seismic sequence. Main advances are expected from the results of these studies, which can have national as well as international broader impact.
Firstly, geotechnical and geophysical investigation will be used together with traditional and remote structural surveys (laser scanner); new high-resolution three-dimensional imaging from UAVs will complement ground-based investigations and enhance the interpretation of landslide activity.
The possibility to improve the rock mass characterization through field and laboratory investigations will allow to better assess mechanical properties of rock formations which are widespread in Central Italy. Further, an insight will be given into the geological and geotechnical background of the slope failures and will allow to infer failure mechanisms from field evidence.
Past studies have attributed high rockfall density to topographic effects which can locally modify earthquake ground shaking. The proposed methodology will envisage 2D numerical analyses which can account for stratigraphic and topographic effects. To this regard, the back-analyses of three case-histories subjected to different seismic events will try to clarify the main factors that triggered the mass movements. Specifically, by comparing the shaking effects of a series of events of different magnitude, the amplification phenomena related to the local geology, dynamic conditions and morphological features of the slope will be revealed. The frequency characteristic of an input earthquake and the vibration characteristics, and the relation with the material property of the slope and falling rocks will be also investigated.
Once the capability to reproduce the rockfall occurrences will be established, the models developed will be applied elsewhere on other slopes in order to distinguish the candidates falling rocks on the rocky slopes and to evaluate the applicability of the earthquake response analyses.
Ultimately, the results of the study will allow researchers to better understand and predict earthquake-triggered rockfalls and rockslides, eventually leading to the ability to prevent major failures. These findings will also assist engineers and Civil Protection Department in using improved models for predicting landside susceptibility.
Collaboration with other Researchers/Institutions. This research will be conducted in collaboration with national public institution, such as National Research Council (IGAG) and Provincia di Teramo, and international Universities, such as the Brigham Young University .
Broader Impacts. The results of this research have the potential to increase the ability of engineers and researches to predict and prevent rock slope failures. This will mitigate the economic consequences and social diseases to the transportation network and economically loss of property and could even save lives. The main goal is to disseminate the results of this research to as many audiences as possible and to increase interest in the topic. It is anticipated that publications on leading peer-reviewed journals will result from the research activities.
References
Faccioli, E. (1995). Induced Hazards: Earthquake triggered Landslides, in Proc. of the 5th Int. Conf. on Seismic Zonation, 1908¿1931, 1995