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

3D electrical resistivity tomography technique for the investigation of a construction and demolition waste landfill site

We present the practical application of a 3D electrical resistivity tomography (ERT) geophysical survey conducted in order to calculate the geometrical features and general structure of a construction and demolition waste layer in an old unregulated landfill prior to redevelopment. As traditional geological/geotechnical investigations comprised of cone penetration tests (CPT) failed to provide reliable results, primarily due to the nature of the underlying waste, a geophysical investigation was commissioned and found to be very effective in providing useful and accurate information to the project’s environmental and engineering team. The ERT survey data were collected in parallel equidistant lines and were subsequently merged and inverted as a single 3D dataset. The processed data depicted clearly the interface between the resistive construction waste and the conductive undisturbed host clay layer ranging at depths between 3 and 11 m. As a result of this successful geophysical investigation the total volume of the solid waste materials was calculated to be about 32500 m3. Following the complete removal of the waste it became evident that the ERT geophysical survey results were particularly accurate. As a result, the reclamation constructor was able to carefully plan the required resources for excavating, moving and disposing of the waste. Interpreted ERT data not only defined the thickness of the debris layer and the total volume with a deviation of less than 10%, but also revealed the inner structure of the solid waste layer