Italian journal of engineering geology and environment

Geological Hazards and Cultural Heritage: the 2014 San Leo Landslide (Northern Apennines, Italy) and Its Implications

Lisa Borgatti — 2024-10-08

The geology of the San Leo Cliff (Northern Apennines, Italy)

Alberto Landuzzi — 2024-10-08

The main objective of this work is to deduce the geologic setting of the San Leo cliff from the natural sections exposed in its own rock walls. The line-drawings of the rock walls, coupled with a detailed geologic map and framed in a tectonostratigraphic scheme, allow us to reconstruct a 3D geological model of the San Leo cliff . The interpretation of the collected data also allows us to establish the relationships between lithostratigraphy, tectonics and geomorphology that control the evolution of this spectacular and delicate landscape emergency of Val Marecchia. The 2014 landslide (Borgatti et alii, 2015) has been only the latest event in the evolution of the San Leo cliff , where fractures and faults of Late Pliocene to Present age have predisposed rock masses to fall, so that the current slope morphology is the result of a very long series of rockfalls (Benedetti et alii, 2011).

Earthquakes in the Valmarecchia area (Northern Apennines, Italy)

Caterina Zei — 2024-10-08

The Valmarecchia area, located between the Emilia-Romagna and Marche administrative regions, is characterized by numerous landslides and has been affected by earthquakes occurring both outside and inside its territory. As earthquakes are one of the main causes of gravitational phenomena, we investigated the occurrence of earthquake-induced landslides, starting from the events that were reported as felt in any of the Valmarecchia municipalities. We analyzed their magnitude and distance from the area and identified the seismotectonic areas that generated them. We found that more than half of the earthquakes that hit Valmarecchia historically could have generated shaking-induced landslides; and yet, based on the ample documentation stored in online portals, we also found that the number of earthquakes for which there exists historical evidence for such phenomena is very limited. This is likely the result to lack of information on the correlation among earthquakes and landslides, possibly justified by the local historical and geographical context and by the seismotectonic marginality of Valmarecchia, located off the main seismogenic trends of the Italian peninsula. We aim to improve knowledge on Valmarecchia seismicity and to illustrate a methodology for identifying both earthquake-induced effects and the areas that are prone to these phenomena.

The San Leo Cliff in the Northern Apennines, Italy: slope instability and risk mitigation measures after the 2014 landslide

Claudio Corrado Lucente — 2024-10-08

The medieval town of San Leo and its fortress have been classifi ed as a “settlement to be consolidated”, following the Italian law. They rise on a rocky, steep cliff that is prone to failure, as well as the entire area surrounding the cliff is subject to slope instability phenomena. Over the past seventy years, a series of consolidation works have been conducted on the rock walls. These interventions focused mainly on the south face, where the town and its access road are located, and on the east face, particularly in the area where the fortress is situated. Since the 1980s, efforts to reduce the risk have also focused on the base of the cliff with the aim to prevent its erosion and undermining. The latter is considered the cause of major rock failures, such as the landslide that occurred in 2014. Despite past interventions, however, landslide risk in the San Leo cliff still remains high. The slope failure of 2014 marks a dividing line: after that a comprehensive multidisciplinary study was started. The study involved different investigation and monitoring techniques in order to understand, prevent, and reduce landslide risk. The in-depth knowledge gained through this study was crucial in managing the emergency after the collapse, providing the essential elements for defi ning risk scenarios and for planning and designing interventions to reduce risk after the emergency phase. These interventions were carried out on the north face of the cliff, where the main landslide occurred in 2014, but also the east and south faces.

Application of numerical methods for the study of the 2014 San Leo landslide (Northern Italy): challenges and lessons learned

Davide Donati — 2024-10-08

The 2014 San Leo landslide is a very peculiar landslide, being controlled by a large number of factors that interacted with each other; each one was in turn critical in driving, promoting, or allowing the slope failure. In the ten years after the landslide event, numerous studies were presented in the form of national and international journal articles, conference proceedings, as well as unpublished technical reports. These projects allowed different aspects and mechanisms to be investigated, progressively enhancing our understanding of the landslide. In this paper, we summarize, review, and discuss the various numerical modelling analyses that have been conducted, in order to outline the foundations on which future investigations may be designed. Considering the in depth understanding that has been gained on the geological, lithological, environmental, and engineering aspects of this site, we suggest that the San Leo plateau may be an ideal engineering geological field laboratory useful in investigating the evolution and instability phenomena that affect sites with similar characteristics within the Marecchia Valley region and beyond.

Evidence of unstable rock cliffs from vibrational behavior: challenges in coupling engineering-geological and geophysical approaches

Salvatore Martino — 2024-10-08

Over the last decades, engineering-geology has increasingly made use of multidisciplinary approaches aimed at detecting physical-mechanical characteristics of the subsoil in the near surface, to better understand and monitor the dynamics of natural processes as potential causes of natural risk. Geophysical investigations by passive seismic in the near surface became over time a fundamental tool to interpretate the vibrational behaviors of rock volumes, already displaced by physical discontinuities (i.e. rock mass joints). The frequencies of oscillation, amplified by dislodged blocks, are polarized in specific directions, and related to eigenmodes which depend on their degrees of freedom, mass, stiffness and damping coefficient. On the other hand, the superposition of soft soil on bedrock induces stratigraphic amplification which may not be polarized if they occur in properly one-dimensional contexts. This contribution focuses on the aforementioned investigation techniques, through a review of case studies which allowed learning their diagnostic potential and, at the same time, conceptualizing their functionality and adaptability (under certain representativeness constraints) to different morphoevolutionary contexts. The hazard zoning for rock landslide, which have been created to date by these techniques, appear to be fully integrated into thematic maps on active landslide processes and related spatial distribution, seismic microzonation maps and related areas of instability, residual risk perimeter maps aimed at preventing access or usability of urbanized areas.

Rock engineering and its obsession with rock bridges: why everything we call real cannot be regarded as real

Davide Elmo — 2024-10-08

Rock bridges are critical in determining the stability of rock slopes and underground excavations. However, measuring them is impossible since their definition extends beyond a mere geometrical problem. Rock bridges are understood primarily in the context of rock mass strength, representing known unknowns akin to the principle of complementarity in physics. The current understanding suggests that while we can measure rock bridges post-failure, their pre-failure definition and measurement elude us. Historically, researchers have focused on the geometric perspective of rock bridges, with limited attempts to investigate actual field evidence. This has led to a disconnect between the theoretical problem and practical measurement. Since Terzaghi first highlighted this issue in 1962, more progress has yet to be made in addressing the fundamental limitations of our understanding of rock bridges. This paper argues for a paradigm shift towards analyzing rock bridges through the lens of rock mass damage and recognizing that rock bridge strength is directionally dependent.