Fabio Pratesi

Badland susceptibility assessment in Volterra municipality (Tuscany, Italy) by means of GIS and statistical analysis

Badlands can be defined as complex and peculiar types of erosional formations that develop in clayey environments and are mainly favoured by lithological and topographic features, as well as by markedly seasonal climate. This work aims at assessing badland susceptibility in Volterra municipality located in Tuscany region (Italy) by means of bivariate statistical analysis implemented in a geographic information system. The Volterra municipality is affected by intense soil erosion processes, including rill and gully erosion usually turned out as badland forms, mostly occurring on Pliocene–Pleistocene clayey sediments. Firstly, an inventory of 234 badland areas was produced on the basis of an available pre-existing database, integrated with the interpretation of aerial photographs and supported by a field survey. Badlands were distinguished in type A and type B, according to different evolutional stage, vegetation presence and consequently different landforms. Then, nine geoenvironmental factors supposed to be predisposing for badland occurrence were chosen and combined with the spatial frequency of badland areas derived from the inventory, through Information Value Statistic approach. The result was a badland susceptibility map that highlights a strong control of lithology, slope gradient and land use in conditioning badland development in the investigated area. The effectiveness of the performed model was demonstrated by a validation test computed through a receiver operating characteristics analysis. The outcomes of this work provide an updated badland database that is useful for soil erosion management and further land-use planning within the Volterra municipality.

Building Deformation Assessment by Means of Persistent Scatterer Interferometry Analysis on a Landslide-Affected Area: The Volterra (Italy) Case Study

In recent years, space-borne InSAR (interferometric synthetic aperture radar) techniques have shown their capabilities to provide precise measurements of Earth surface displacements for monitoring natural processes. Landslides threaten human lives and structures, especially in urbanized areas, where the density of elements at risk sensitive to ground movements is high. The methodology described in this paper aims at detecting terrain motions and building deformations at the local scale, by means of satellite radar data combined with in situ validation campaigns. The proposed approach consists of deriving maximum settlement directions of the investigated buildings from displacement data revealed by radar measurements and then in the cross-comparison of these values with background geological data, constructive features and on-field evidence. This validation permits better understanding whether or not the detected movements correspond to visible and effective damages to buildings. The method has been applied to the southwestern sector of Volterra (Tuscany region, Italy), which is a landslide-affected and partially urbanized area, through the use of COSMO-SkyMed satellite images as input data. Moreover, we discuss issues and possible misinterpretations when dealing with PSI (Persistent Scatterer Interferometry) data referring to single manufactures and the consequent difficulty of attributing the motion rate to ground displacements, rather than to structural failures.

Early Warning GBInSAR-Based Method for Monitoring Volterra (Tuscany, Italy) City Walls

Ground-based synthetic aperture radar interferometry (GBInSAR) remote sensing technique has been repeatedly proved an effective tool for monitoring built environment affected by structural and geological criticalities. In this paper, it is described how this technique can be successfully applied for early-warning procedures and detection of ongoing deterioration processes on archeological and cultural heritage sites. An integrated approach of GBInSAR and terrestrial laser scanner (TLS) technologies was performed on Volterra test site (Tuscany, Italy), where a sudden collapse of a 35-m wide section of city walls occurred on January 31, 2014. The installed early-warning monitoring system is capable of an accurate and focused real-time displacement detection of the south-western side of the city including walls, buildings, and monuments, thus allowing prompt interventions for citizens safety and conservation purposes. The effectiveness of this alert technique became evident when the precursors of a second impressive wall collapse were clearly detected. From the beginning of the GBInSAR monitoring, we measured a constant displacement velocity of 0.1 mm/h in correspondence to a 15-m high wall sustaining the Acropolis and lying an underground parking. After a sudden increase of velocity values up to 1.7 mm/h, the local authorities were alerted so that they had time to interdict the area to citizens and to take adequate safety countermeasures two days before the collapse.

Rating health and stability of engineering structures via classification indexes of InSAR Persistent Scatterers

We propose a novel set of indexes to classify the information content of Persistent Scatterers (PS) and rate the health of engineering structures at urban to local scale. PS are automatically sampled and grouped via ‘control areas’ coinciding with the building and its surrounding environment. Density over the ‘control areas’ and velocity of PS are converted respectively into: Completeness of Information Index (Ici) that reflects the PS coverage grade; and Conservation Criticality Indexes (Icc) which rate the health condition of the monument separately for the object and surrounding control areas. The deformation pattern over the structure is classified as isolated (i) or diffused (d) based on the Velocity Distribution Index (Ivd). Both Ici and Icc are rated from A to E classes using a colour-coded system that intentionally emulates an energy-efficiency scale, to encourage the exploitation of PS by stakeholders and end-users in the practise of engineering surveying. Workability and reliability of the classification indexes are demonstrated over the urban heritage of Florence, Italy, using well established ERS-1/2 (1992–2000) descending, ENVISAT (2003–2010) ascending and descending PS datasets. The indexes are designed in perspective of handling outputs from InSAR processing of higher-resolution time series.

Structural Assessment of Case Study Historical and Modern Buildings in the Florentine Area Based on a PSI-Driven Seismic and Hydrogeological Risk Analysis

C-band medium-resolution Persistent Scatterer Interferometry (PSI) data from ERS-1/2, ENVISAT and RADARSAT-1 were used to establish a classification method preparatory to seismic and hydrogeological risk assessment of historical buildings in urban areas. Tests were conducted over the heritage city of Florence, Italy, using a multidisciplinary approach which takes into account geological and environmental factors of hazards, along with parameters related to conservation history of the monuments and the possible sources of damage commonly found within an urban context. The case study herein presented confirm the advantages of PSI against its well-known limitations, and demonstrate how PSI can be used to support subsequent structural analyses of buildings.

Seismic pounding mitigation of a modern heritage R/C bell tower

Pounding is one of the greatest sources of seismic vulnerability of pre-normative R/C structures, as they have often been built at poor distance from adjacent buildings. The effects of pounding can be particularly severe in slender modern R/C heritage structures, including civic or bell towers. An emblematic case study falling in this class of structures, i.e. a monumental R/C bell tower constructed in the early 1960s to replace the former 19 th century tower of the Chiesa del Sacro Cuore in Florence, is analyzed in this paper. In order to assess the effects of pounding, a non-linear dynamic finite element enquiry was carried out by simulating collisions with a multi-link viscoelastic contact model originally implemented in this study. The survey results show that pounding affects the seismic response of the bell tower and the church as early as an input seismic action scaled at the amplitude of the normative basic design earthquake level. A retrofit hypothesis to prevent pounding is then proposed, which consists in linking the two structures by means of a pair of fluid-viscous dampers. The technical implementation of this rehabilitation strategy and the benefits induced in the response of the bell tower are discussed in detail in the paper.

Damped interconnection-based mitigation of seismic pounding between a R/C tower and a masonry church

Damped interconnection represents an advanced strategy to mitigate the effects of seismic pounding between adjacent structures built at poor mutual distance. The effects of pounding can be particularly severe in slender R/C structures, including civic or bell towers. An emblematic case study falling in this class of structures, i.e. a monumental R/C bell tower constructed in the early 1960s in Florence, is analyzed in this paper. In order to assess the effects of pounding, a non-linear dynamic finite element enquiry was carried out by simulating collisions between the tower and the adjacent masonry church with a multi-spring-damper viscoelastic contact model, originally implemented in this study. The survey results show that pounding affects the seismic response of the two buildings as early as an input seismic action scaled at the amplitude of the normative basic design earthquake level. A damped interconnection-based retrofit hypothesis to prevent pounding is then proposed, which consists in linking the...