Electrical resistivity tomography of a masonry bridge: assessing water infiltration on Prebends Bridge, Durham, UK.

Non-invasive imaging methods are a useful tool in informing conservation actions for historical buildings. Electrical Resistivity Tomography (ERT) is widely used in geophysics to image the subsurface but has been seldom used for non-invasive imaging of small-scale masonry structures. Here, we propose an adaptation of the method allowing non-damaging investigation of larger-scale stone structures. We report results of an ERT survey of Prebends Bridge in Durham, a heritage masonry structure constructed in 1778. Our assessment is based on data acquired on the paved top surface of the bridge, which is subsequently modelled and inverted with the use of open-source software. Final images of the internal structure of the bridge reveal areas of lower electrical resistivity, that we interpret as representing regions of water saturation. Locations of low resistivity areas are in good agreement with the structural defects and patches of seepage observed externally. These results will help inform remediation work, to preserve this historical structure from further water damage. In future studies, time-lapse imaging may help to highlight water pathways unambiguously (through comparison of dry/wet periods), while additional electrode arrays installed on the sides/base of the structure could be used to better constrain 3D internal structure. [ABSTRACT FROM AUTHOR]