Multi-scale water distribution imagery in building heritage using Electrical Resistivity Tomography (ERT) and Infra-Red Thermography (IRT): Application to Gallo-Roman masonry submitted to water-table rising periods
Résumé
The archaeological site of Vaux-de-la-Celle, located at 60 km North-West of Paris, is an outstanding example of
Gallo-Roman heritage in France. The site concentrates various structures built between de 2nd and 4th century
AD. Specially, the theatre, that could accommodate ten thousand people and the temple partially erected with three
Nymphaeum (ceremonial bath). This archaeological site is remarkable for the magnificence of the vestiges and
also for the hydrogeological context related to its location within a valley where the water table reaches level of the
surface. The Temple structure is constructed at the lowest part of the valley with its foundations in direct contact
with the vadose zone where the water table fluctuates. This particular condition provides the basis of the study case
that concerns fluctuations of the water content and distribution within the porous materials and its impact regarding
salt weathering.
Water distribution in a masonry is a determining factor in the frame of the salt weathering processes. The aim of this
study concerns the application of a Non-Destructive Technic (NDT) that allows to determine the water distribution
within the building masonry, in particular the Electrical Resistivity Tomography (ERT) and Infrared Thermography
(IRT) method. The ERT method enables to image the spatial and/or temporal variation of the electrical resistivity
related to the water and salt content distribution within the structure while IRT provides the boundary limit conditions
by the means of surface thermograms.
Experiments in the lab are performed in order to analyse the electrical response of the materials. Indeed, the electrical
resistivity of the materials is measured at different degrees of saturation, going from dried state to complete
saturation. In addition, a water capillary imbibition test is performed on a stone core of a limestone rubble from
the archaeological site. During the imbibition test the changes of the physical proprieties concerning the electrical
resistivity and surface temperature are monitored by applying the ERT and IRT methods. The imagery methods
are combined with numerical models to have a better understanding of the capillary rise phenomena. Finally, this
methodology is applied on a wall of the Gallo-Roman temple of the archaeological site in order to survey the
evolution of water