High definition NDT investigation of large statue pedestal

A number of marble sculptures by Michelangelo Buonarroti are hosted inside the Galleria dell’Accademia in Florence and in recent years their preservation, including seismic risk assessment, has been at the centre of attention by the management of the Gallery. The most important of these sculptures, the David, was carved by Michelangelo between 1501 and 1504. This sculpture has exceptional dimensions: 5.16 meters in height and nearly 6 tons in weight. The marble block used for the statue, from a quarry near Carrara, has unfortunately poor mechanical properties. In the second half of 19th century, the presence of cracks was detected on the marble surface, together with a degradation of the pedestal, which had caused a considerable tilt of the statue in forward direction. After centuries of outdoors exposure, in 1873 David was moved from Piazza della Signoria to the inside of Galleria dell’Accademia, where it was placed in the correct vertical position. The initial statue design was for a view from long distance. The 19th C. pedestal, although smaller than the original one, is 1,60 m high. Still, when looking at David in Galleria dell’Accademia, it appears very small in comparison to the sculpture. The wanted result is the David to look bigger. The pedestal has the important function to physically support this considerable statue. Further, if a system for seismic isolation of David has to be provided, it is essential the knowledge of the pedestal’s internal structure and mechanical characteristics. Unfortunately, the documentation about this new pedestal is quite limited. The non-destructive investigations conducted on the pedestal had the aim of gaining a better knowledge about its construction: inner shape of the outer marble ashlar slabs, construction materials used for the core of the pedestal, presence of possible metal supports, voids. Extensive data collection was carried out on all four sides of the pedestal by means of medium-high and high frequency GPR antennas. Example output data will be shown and discussed.