First Investigations of In Situ Electrical Properties of Limestone Blocks of Ancient Monuments

International audienceIn situ rapid electrostatic investigations on calcareous stones of monuments provide information that strongly correlates with the geological characteristics of the stone and proves to be efficient for provenance identification and successive restoration. With a portable device, it is now possible to scan several thousand blocks on a face of a monument in a few hours. The evolution of the religious building construction practices between the 13th and the 17th centuries is studied. From the petrophysics point of view, the results clearly indicate a marked linear correlation between electrical conductivity and dielectric permittivity. This fact, which agrees with Maxwell–Wagner polarization modelling, confirms the part played by the clay content in the electric properties of the dry carbonate rocks constituting the monument stones. A first test using X-ray scattering analysis shows the part played by the relative content of illite, which is correlated with a decrease of the resistivity

Clay fine fissuring monitoring using miniature geo-electrical resistivity arrays

Abstract This article describes a miniaturised electrical imaging (resistivity tomography) technique to map the cracking pattern of a clay model. The clay used was taken from a scaled flood embankment built to study the fine fissuring due to desiccation and breaching process in flooding conditions. The potential of using a miniature array of electrodes to follow the evolution of the vertical cracks and number them during the drying process was explored. The imaging technique generated two-dimensional contoured plots of the resistivity distribution within the model before and at different stages of the desiccation process. The change in resistivity associated with the widening of the cracks were monitored as a function of time. Experiments were also carried out using a selected conductive gel to slow down the transport process into the cracks to improve the scanning capabilities of the equipment. The main vertical clay fissuring network was obtained after inversion of the experimental resistivity measurements and validated by direct observations

Archaeological Prospecting using Electric and Electrostatic Mobile Arrays

L'article est consultable sous le lien [https://onlinelibrary-wiley-com.inshs.bib.cnrs.fr/doi/10.1002/%28SICI%291099-0763%28199812%295%3A4%3C239%3A%3AAID-ARP106%3E3.0.CO%3B2-N]International audienceThe latest generation of mobile electric and electrostatic arrays allows the measurement of the apparent resistivity over large areas with a high spatial sampling and for several depths of investigation. This paper presents three experiments undertaken over three archaeological sites of three different historical periods (Iron Age, Roman, medieval) and three different subsoil covers (meadow, ploughed field, asphalt). The archaeological structures (ditches, enclosures or walls) are described with a good accuracy. They are integrated in their environmental and geological context