Misure di resistività finalizzate allo studio del sito archeologico internazionale di Torracia di Chiusi mediante strumentazione OhmMapper

The paper describes the findings of a geo-electric study conducted at the archaeological site of Torraccia di Chiusi (Siena Province) with the use of soil resistivity modelling. In collaboration with the Departement d’Archeologie et Histoire de l’Art (Universite catholique de Louvain, Belgium) and the Centro di GeoTecnologie (Universita degli Studi di Siena), a new, non-invasive instrument, named the OhmMapper, was used for the first time in an archaeological context to provide geophysical sections of the terrain. The aim of the study was to evaluate the nature and distribution of the buried anthropogenic structures and to properly locate them on the map without the necessity of excavating. The site, located in the valley of the Foci river, has been described as a long lasting settlement (III to VII centuries AD, although ceramics dating to the II century BC have been uncovered). The OhmMapper is a capacitively coupled resistivity meter that measures the electrical properties of rocks and soil without ground stakes used in traditional resistivity surveys. A simple coaxial-cable array with transmitter and receiver sections is pulled along the ground either by a single person or attached to an all-terrain vehicle. The dipole-dipole configuration enables the instrument to immediately pick up the horizontal variations in resistivity, thereby enabling the user to identify structures such as walls or cavities. With the OhmMapper, nine sections were made around the perimeter of the area already excavated to collect data on the presence, depth, and dimensions of anthropogenic structures. The results from the sections were refined and placed on a map using an ArcGIS platform. The interpretation of the nine sections resulted in a new hypothesis on the buried anthropogenic structures and a new model of the natural landscape that existed at the site prior to its construction.