GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 3.2 ___ GNGTS 2023 antennas are available ranging in center frequency from 25 to 1500 MHz. The selection of antenna is dependent on the desired feature resolution and depth of penetration and the typical range is 400 to 1500 MHz. GPR data are collected in either a 2-D (distance and time) or 3-D (x, y, and time) fashion, depending on the application. The data processing steps may include a variety of geophysical algorithms; the steps performed depend on the data characteristics and project goals. The effectiveness of GPR scanning and interpretation is highly dependent on the existing field conditions. Heavily reinforced members may shield radar signals from deeper material or features. Deep, small diameter features are more difficult to detect than shallow, large diameter features. Moisture content and clayey materials limit signal penetration. Ambient electromagnetic noise may distort data. For depth determination, velocity estimation must be performed from a location of known thickness. Typical accuracies for linear feature centreline locations are ± 0.5 to ±2.0 cm. For this specific case it will be used two different system: ● For the bridge deck Stream C multi array GPR combined to a GPS system was used for mapping of buried utilities. The Stream C has 1 main antenna made by 32 dipoles, where 23 are available in VV and 9 in HH respectively. Every single dipole is 4 cm spaced and they guarantee a 92 cm lateral coverage for every single radar scan (Fig.3a). ● For screening the arcs an antenna with central frequency of 900 MHz was used for identify possible structural defects (Fig.3b). References Scott M, Rezaizadeha A, Delahazab A, Santosc C G, Moored M, Graybeale B, Washerf G. , 2003A comparison of nondestructive evaluation methods for bridge deck assessment, NDT&E Int., vol. 36 (pg. 245-55). Soldovieri F, Solimene R , 2010, Ground Penetrating Radar Subsurface Imaging of Buried ObjectsVienna, AustriaRadar Technology IN-TECH(pg. 105-26).