GPR prospecting on masonry walls in a high seismic hazard region: the resilient Castellina Museum of Norcia (Central Italy).

In regions characterized by high seismic hazard, historical masonry buildings are periodically shaked and damaged by strong earthquakes. Their conservation represents one of the major challenges for scientific research and society, especially when  resilient heritages have high artistic and cultural values. After destructive instrumental and historical earthquakes, such historic constructions were subjected to restorations and changes of their original configuration. The evaluation of  masonry mechanical  for the analysis of static and dynamic behaviour of historic structures is conventionally done using invasive methods. However, also the application of  Non-Destructive Testing (NDT) techniques (e.g. geomatic and geophysical ones) is progressively growing, to reduce the amount of invasive interventions. GPR is one of the non-invasive techniques providing high-resolution images, also used for masonry wall diagnostics. We carried out a Ground Penetrating Radar (GPR) survey at the Castellina Museum in Norcia, an historical bounding located in the city centre, damaged by the long-lasting seismic sequence occurred in 2016-2017 (mainshock Mw=6.5). We aimed to obtain non-destructive information on the internal structure of a masonry wall located at the ground floor, being the facade of a formerly existing (later incorporated) edifice, named Palazzo del Podestà. Based on the results of preliminary Sonic tests (ST) surveys, investigating the homogeneity degree of the masonry, possible voids, cracks and degraded areas, we collected several Common Offset GPR profiles, using 1 GHz and 1.5 GHz antennas. The results clearly show the backside of the walls, as well as their heterogenous internal structure. GPR mapping also show a very variable signature across different wall sectors, showing a significant amplitude decay of the main reflections due to an increase of the electrical conductivity, possibly linked to moisture changes or degraded sectors. Further geophysical investigations and chemical analysis will be achieved to shed light on these hypotheses and to assess the state of conservation of the masonry, for a proper design of subsequent remediation interventions. This project is founded by the Università degli Studi di Perugia (Finanziamento di Progetti di Ricerca di Ateneo Anno 2021, P.I. Prof.ssa Carla Falluomini, WP 2-4). The authors thanks the Municipality of Norcia for their kind support and collaboration).