PSI - Issue 62

Nicola Perilli et al. / Procedia Structural Integrity 62 (2024) 538–545 Nicola Perilli, Stefano Stacul, Massimiliano Lombardi, Nicola Nenci, Nunziante Squeglia / Structural Integrity Procedia 00 (2019) 000 – 000 3

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Diagnostic Area : Considering that landslides are usually not isolated phenomena as related to conditioning and/or triggering factors, the first area that should be investigated should be large enough to allow the characterization of the geomorphological and geological context of the surrounding zones of the Geomorphological Significative Area and to check if the area within which the bridge is located is currently affected by landslides or is proneness to be affected by landslides. Therefore, the investigation of the Diagnostic Area, with respect to the Geomorphological Significative Area, is also necessary to identify previously mapped (Recognized) landslides, and to check their characteristics including the state of activity, the velocity, and the magnitude (i.e., size). As regards the geomorphological aspects, particular attention will be paid to the characterization of the physiographic units, the main geomorphological units and processes that shape the slopes of the Diagnostic and Geomorphological Significative Areas. Regarding the characterization of the geological context, it should include the definition of the lithologies, of the mapped lithostratigraphy units and, the lithotechnical units outcropping in the Diagnostic Area already involved in landslides or which can promote landslides. Geomorphological Significative Area : First based on a desk study and then confirmed during the Periodic Field Survey of the Relevant Area, the investigation of the Geomorphological Significative Area is aimed to refine the characterization of the topographic surface including the presence of rivers/channels, the lithological features, the accurate characterization of the vegetation cover and of the land use. The accurate investigation of the Geomorphological Significative Area will allow to identify the features of relief, the slopes and the presence of cliffs and terraces; and the relationship between the inclination of the strata compared to the inclination of the slope should be carefully checked. The investigation will also allow to evaluate the degree of disarticulation or dismembering of the rock mass and/or correctly describe the engineering properties of soil, to check and evaluate the type and the density of the vegetation coverage, the type of land use, the changes in land cover over time. Relevant Area : This area is the key area that needs to be carefully investigated. The investigation should provide the accurate characterization of the slope (including the profile of the slope and the position of the bridge with respect to the slope) and, the description of the river crossed by the bridge including its sinuosity, position respect to the riverbanks, and the presence of erosive phenomena at the base of the slope and riverbanks. The investigation should be extended upwards and downwards the bridge. Moreover, the description of the vegetation cover and the land use should also be included to identify precursor evidence of potential landslides, which will be monitored during the subsequent Periodic Field Surveys. Then it is necessary to: • check whether a bridge is already involved in a landslide or is threatened by a potential landslide, • check which is or could be the type of landslide according to the options available in the Field Sheet Form, • evaluate the position of the landslide with respect to the bridge, • recognize the distribution of the activity, referring to how and where the landslide is moving, • identify the presence of source areas of potential landslides (Perilli et al., 2024, in this volume), especially in those situations that can generate rapid to extremely rapid phenomena (i.e., debris flow, mud flow, falls etc…) . Particular attention should be given to the characterization of the engineering properties of the soil, the estimation of its thickness, distinguishing between predominantly fine or predominantly coarse-grained materials. A description of the type of texture, i.e. supported by clasts or matrix, and the evaluation of the percentage of fine fraction and the size range of the clasts is also recommended. For the rock mass is necessary to evaluate the degree of fracturing, the size of the rock matrix and its alteration range. Also, the estimation of the percentage of the pelitic fraction could be useful to distinguish between successions with or without intercalation of pelitic intervals (e.g. Maiolica Formation) and successions characterized by the significant presence of pelitic alternance or even the predominance of pelitic intervals (e.g. Tuscan Shale Formation).