NDT for Structural Diagnosis for Marble Columns. The Case of San Marco Basilica in Venice, Italy

Sonic tests are well-known non-destructive analysis technique (NDT). Independently or in combination with other examination techniques, they are widely used to understand and qualify structural elements and their mechanical properties, detect the presence of inner voids and flaws, and control the effectiveness of the structural consolidation. This paper presents the results of the combined analysis method, merging different NDTs such as visual inspection and sonic tomography mapping for columns in San Marco Basilica in Venice, Italy. The aim of the study was to assess the structural properties of these elements and to understand and locate the potential ongoing mechanical deterioration. Tomography maps were constructed in selected horizontal and vertical sections, for more profound study with three-dimensional analysis approach. The performed analysis confirmed the suspected mechanical deterioration in all studied stone elements. Most of the areas that exhibit low sound velocity, overlap with the highly deteriorated exterior zones previously identified though the visual surveys. The NDT approach allowed the identification of the types of structural deterioration, and their profound study in three-dimensional space.