New developments of sonic tests applied to thick masonry structures

Among the different typologies characterizing historic masonry structures, those witch present the most unknown physical and mechanical properties of their internal components, are the structures shaped by massive masonry The reference is made to examples like the lower part of bell towers, high ditch walls of citadels, retaining walls of river and canals, as well as spandrels and piers of arch bridges. How to know the effective structural and load bearing hidden thickness as well as the internal grade of integrity of the wall or pier is still at present a debating issue. Among the wide variety of sonic methods used for detection of internal discontinuities, the Spectral Analysis of Surface Waves (SASW) was developed since decades ago, with different applications, mainly in geothecnical area and reinforced concrete structures, both in the time domain and the frequency domain. in the case of massive masonry elements, techniques analyzing and processing the data with models using phase velocity, frequency-wave number and power spectral analysis seem to present high reliability of detecting the material discontinuities, even of small dimension. Recalling the actual background of sonic non-destructive test different applications, the paper describes the calibration procedure used and the techniques implemented, in term of technological in-situ application and data processing, for the investigation of a retaining masonry wall of an historic water canal near the masonry abutments of a bridge, interested by heavy traffic downtown Milan.