A Diagnostic Method for the Pavement Conservation of the Great Synagogue of Florence (Italy)

The Great Synagogue of Florence is one of the most important and beautiful European synagogues. Its design includes many Moorish-style motifs, typical of Spanish architecture; the pavement is characterized by a geometric four-colour decoration obtained by the use of red limestone, and grey, yellow and white marbles. The temple was damaged several times in the past and very recently its floor showed a worrying collapse in some areas of the hall; the subsidence caused also small cracks, and degradation of the surface stones. For this reason, various diagnostic investigations were carried out; an exploratory test by drilling a stone tile allowed us to know the stratigraphy under the pavement; a dynamic penetrometer test inside this hole permitted us to verify the stability conditions of the terrains. Furthermore, geophysical and geognostic survey through a Ground Penetrating Radar (GPR) and an Electric Resistivity Tomography (ERT), with two drillings equipped with piezometers, made it possible the geotechnical characterization of the synagogue geological substrate. In addition, the materials used in the pavement were collected and compositionally characterized, for possible replacement. The diagnostic investigations provided an overall cognitive framework of the Synagogue’s soil foundations, filling, and floor revetment. In particular, the diagnostics evidenced the presence of numerous voids of different sizes under the pavement. The obtained data represent an essential step to decide the most appropriate restoration campaign.