Ground Penetrating Radar Applications on the Facade of Milan's Cathedral (Italy)

摘要

Ground Penetrating Radar (GPR) has been widely applied to evaluate the state of preservation of the Facade of Milan's Cathedral during the present restoration and maintenance project started in 2003. This technique has already been applied and tested on the interior wall of the Cathedral. For survey on the scaffolding, the GSSI SIR20 instrument equipped with 900 and 400 MHz antennas, was used. The typical goals of the structural survey were: i. marble block thickness; ii. State of preservation of masonry; iii. adhesion of blocks to masonry; iv. presence of cavities, fractures, metallic inserts or other anomalies. The inspected surface was about 2500 m~2 and 4510 marble blocks were analysed; the average thickness was 25 cm; the state of preservation of masonry was quite good, especially in the higher part, while the degree of detachment of the blocks from the masonry was not negligible in some areas. Custom-made ETRadar software was developed to store and integrate the structural information by GPR in the vectorial model of the Facade. This AutoCAD application requires a semiautomatic elaboration process of data. The results are thematic layers of structural features, i.e. fractures, cavities, detachments, marble blocks, cramps etc., drawn in a three-dimensional space down to the investigated depth. Finally, every marble block was defined as closed geometric object in the 3D vectorial model.