Three-dimensional electrical and seismic tomography for assessing the state of conservation of a masonry wall

Geophysical non-destructive testing has been applied worldwide during last decades for understanding the inner geometry, the constructive materials and the degree of conservation of ancient buildings affected by the ravages of time, human interventions or natural phenomena (e.g. Polymenakos et al. 2005; Tsokas et al., 2013). The integrated approach presented in this work encompasses the use of Electrical Resistivity Tomography (ERT) and seismic tomography aiming to assess the current state of conservation of a Roman masonry building, named "Casa di Diana", located at the Ostia Antica archaeological site (Rome, Italy). Three-dimensional ERT and seismic tomography investigations were focused on an inner wall, made in opus caementicium, prone to both rising damp and cracking phenomena, in order to reconstruct a 3D model where anomalous zones would be highlighted. ERT dataset were inverted with the VEMI interface (De Donno & Cardarelli, 2015), while seismic tomography inversion was performed by means of the algorithm after Cardarelli & Cerreto (2002). Results show that low resistivity and P-wave velocity values can be associated to the presence of the inner mortar, while higher values of both parameters were observed for the existence of the outer brick component. Overall, with reference to a previous work where a small-scale sample of a Roman masonry wall was analysed in the laboratory using seismic tomography (Cardarelli & de Nardis, 1999), the brick part seems to be in good conditions (optimal VP=1400 m/s, recovered VP=1300 m/s), while the low velocity values of the mortar (optimal VP=500 m/s, recovered VP=250 m/s) can potentially represent an anomaly due to degradation phenomena. Therefore this approach can be employed to reconstruct a 3D model of an archaeological wall in order to plan the recovery actions.