Margherita Cecilia Spreafico

Back Analysis of the 2014 San Leo Landslide Using Combined Terrestrial Laser Scanning and 3D Distinct Element Modelling

Landslides of the lateral spreading type, involving brittle geological units overlying ductile terrains, are a common occurrence in the sandstone and limestone plateaux of the northern Apennines of Italy. The edges of these plateaux are often the location of rapid landslide phenomena, such as rock slides, rock falls and topples. In this paper, we present a back analysis of a recent landslide (February 2014), involving the north-eastern sector of the San Leo rock slab (northern Apennines, Emilia-Romagna Region) which is a representative example of this type of phenomena. The aquifer hosted in the fractured slab, due to its relatively higher secondary permeability in comparison to the lower clayey units leads to the development of perennial and ephemeral springs at the contact between the two units. The related piping erosion phenomena, together with slope processes in the clay-shales have led to the progressive undermining of the slab, eventually predisposing large-scale landslides. Stability analyses were conducted coupling terrestrial laser scanning (TLS) and distinct element methods (DEMs). TLS point clouds were analysed to determine the pre- and post-failure geometry, the extension of the detachment area and the joint network characteristics. The block dimensions in the landslide deposit were mapped and used to infer the spacing of the discontinuities for insertion into the numerical model. Three-dimensional distinct element simulations were conducted, with and without undermining of the rock slab. The analyses allowed an assessment of the role of the undermining, together with the presence of an almost vertical joint set, striking sub-parallel to the cliff orientation, on the development of the slope instability processes. Based on the TLS and on the numerical simulation results, an interpretation of the landslide mechanism is proposed.

Terrestrial Remote Sensing techniques to complement conventional geomechanical surveys for the assessment of landslide hazard: The San Leo case study (Italy)

Abstract The San Leo village, located near to Rimini (northern Italy), was built in the medieval period on the top of a calcarenite and sandstone plateau, affected by lateral spreading associated with secondary rock falls and topples. In fact, a number of landslides endangered the historical town since centuries. In order to describe the structural features driving these slope instability phenomena, a complete Terrestrial Laser Scanner (TLS) survey all around the San Leo cliff was performed. Moreover, Close-Range Photogrammetric (CRP) surveys and conventional geomechanical surveys on scanlines have been carried out. The 3D geometry of the cliffs was extracted and critical areas have been investigated in detail using dense Digital Surface Models (DSMs) obtained from CRP or TLS. The results were used to define the structural features of the plateau, to recognize more fractured areas, and to perform kinematic analyses, in order to assess the joint sets predisposing to slope instability at the cliff scale. The creation of a 3D model was also fundamental for the implementation of the geological model to be used in numerical modelling for hydrogeological characterization and slope stability analyses.

Remote Sensing Techniques in a Multidisciplinary Approach for the Preservation of Cultural Heritage Sites from Natural Hazard: The Case of Valmarecchia Rock Slabs (RN, Italy)

The Valmarecchia area (RN, Italy), located between the Emilia-Romagna and Marche regions, displays peculiar geological features, being characterized by rocky slabs lying on gentle slopes. The main fortified villages of the area, remarkable for historical and artistic assets, were built in the medieval period on these slabs for defense purposes. The area is affected by widespread landslide phenomena, involving both the rocky slabs and the underlying clayey shales. The main phenomena acting on the slabs are lateral spreading, with associated rock falls and topples. In this area, a multidisciplinary project, involving different expertise, like geology, geodesy, geomorphology, hydrogeology, soil and rocks mechanics is ongoing. In this particular context, in order to achieve a clear recognition of the instability phenomena, it is necessary to understand the movement patterns and the eventual differential displacement occurring in the slabs. Monitoring activities, joined with geological and geomorphological interpretation, are one of the fundamental step for a deep understanding of the movements and for the risk management purposes. In many cases, the monitoring system is missing or only poor data are available, therefore an approach for the Permanent Scatterers (PS) data analysis has been used, combining analysis on the PS velocity, on the direction of the movement and statistical consideration on the time series trend. Some preliminary results regarding the rock slab on which the town of Verucchio (RN, Italy) is located are here presented.

Hydrogeological features of a highly fractured rock-slab

In many geological contexts, the hydrogeological features of highly fractured rock slabs can drive slope instability processes. This is the case of San Leo (northern Apennines of Italy), where groundwater processes were recognized as predisposing factor for the last large-scale rock fall that took place the 27th of February 2014. In the present work, the hydrogeological features of the San Leo slab were analyzed by means of spring-discharge analysis, piezometric monitoring data and slug tests. The maximum spring yield, the depletion coefficient and the hydraulic conductivity values were estimated. Time-series analyses were used to better understand the groundwater behavior within the rock slab and to estimate its response to rainfall regime. Moreover, the calculation of the groundwater flow direction and modulus in the unsaturated zone was performed. Results highlight the presence of two systems, which are probably related to the characteristics of different joint sets (aperture, spacing); the hydraulic conductivity values were shown to vary with depth. A first general interpretation of the aquifer behavior is given, which is related to the main structural elements of the slab.

Analysis of the interaction between buried pipelines for the transport of fluids and landslides

The aim of this work is the study of the factors that influence the interaction between buried pipelines for the transport of fluids, e.g. gas and water, and Permanent Ground Deformation (PGD), in particular landslides. Pipelines have a fundamental role both in normal operating conditions and in emergency situations. Eventual leakage of the fluids caused by structural damage could cause environmental disasters, financial costs and abuses of resources. In the present work, the methodology proposed by Suresh et al. (2007) was adopted for the calculation of the structural deformation due to the landslide. Furthermore, sensitivity analysis permitted to highlight the influence of different factors, e.g. the pipelines diameter, on the value of the deformation due to their interaction with landslide. The study was applied in different areas of the northern Apennines, selected as representative of the landslide phenomena occurring in Emilia-Romagna region.