Integrated electromagnetic methods for archaeological prospection and stability assessment of anthropogenic mounds: insights into the English Cemetery in Florence

The archaeological interest in anthropogenic mounds as historical products of human occupation generally con- cerns the understanding of their stratigraphic sequence and the discovery of buried structures. Nevertheless, a further key element relies on the assessment of their stability. This is particularly crucial when the conservation history induced relevant alteration of the former configuration, and a potential collapse might cause damages to heritage and actual risk for public safety. To respond to such dual diagnostic need, we propose an integration approach based on Very Low Frequency Elec- tromagnetic (VLF-EM) qualitative method and 2D-Electrical Resistivity Tomography (2D-ERT), to make the best out of these two techniques in light of their frequencies/bandwidth and methods of soil investigation (15-30 kHz and DC, respectively). We present here the results from the experiments performed on one of the test sites selected to validate the pro- posed methodology, i.e. the Protestant Cemetery (the so-called “English Cemetery”) in Florence, Italy, which is a demonstrative example of a huge sample of anthropogenic mounds within urban and rural environments. Located on a topographic relief, the cemetery testifies a long history since Roman times, as proved by historical documentation and the ceramic findings still now discovered on the (sub-)surface. Converted into a cemetery in 1827, the mound appeared as an anomalous outcrop adjacent to the town walls, prior to the final arrangement and reshaping due to the urban renewal of Florence in 1877, which definitely transformed it into a raised graveyard surrounded by boulevards. A campaign of VLF-EM and ERT measurements was performed to ascertain the presence of a buried part of the ancient eastern wall and identify the key areas of concern for the stability. High values of resistivity were clearly detected and mapped by means of 2D-ERT along the AA’ array intercepting the hypothesized location of the buried wall. This measure was cross-validated with the corresponding VLF-EM anomaly profiles, thereby retrieving reli- able geophysical evidences suggesting the presence of buried remains. To correlate the effects of inner structures and soil properties with the stability condition of the mound, crack pattern survey was carried out over the wall containing the mound, jointly to an inspection of the cavities and the interspaces between the exterior masonry surfaces and the rear terrain. The spatial distribution of the opened cracks allowed the actual threat for the stability of the mound to be assessed also in relation to the current positions of the cypresses, periodically replanted for landscape reasons. Interesting insights were obtained by mapping the inclina- tion and tilt direction of the gravestones and funerary monuments, as superficial indicators of ground subsidence and soil compaction/collapse at the top of the mound. The benefits achieved for site management and tombstones maintenance have encouraged the exportation of this approach (highly adaptable to include also GPR and seismic methods) to other case studies, and open to a sustain- able implementation for the investigation of funerary mounds, such as the Etruscan burial mounds

Il sito di Monte Giovi nell’ager Faesulanus

Forthcoming

Il castellum di Poggio Civitella (Montalcino, Siena)

Forthcoming

An electric and electromagnetic geophysical approach for subsurface investigation of anthropogenic mounds in an urban environment

Scientific interest in mounds as geomorphological features that currently represent topographic anomalies in flat urban landscapes mainly lies on the understanding of their origin, either purely natural or anthropogenic. In this second circumstance, another question is whether traces of lost buildings are preserved within the mound subsurface and can be mapped as remnants testifying past settlement. When these landforms have been modified in centuries for civilian use, structural stability is a further element of concern. To address these issues we applied a geophysical approach based on a very low frequency electromagnetic (VLF-EM) technique and two dimensional electrical resistivity tomography (2D-ERT) and integrated it with well-established surface survey methods within a diagnostic workflow of structural assessment. We demonstrate the practical benefits of this method in the English Cemetery of Florence, Italy, whose mixed nature and history of morphological changes are suggested by archival records. The combination of the two selected geophysical techniques allowed us to overcome the physical obstacles caused by tomb density and to prevent interference from the urban vehicular traffic on the geophysical signals. Eighty-two VLF-EM profiles and five 2D-ERTs were collected to maximise the spatial coverage of the subsurface prospection, while surface indicators of instability (e.g., tomb tilt, location, and direction of ground fractures and wall cracks) were mapped by standard metric survey. High resistive anomalies (> 300 and 400 Ωm) observed in VLF-EM tomographies are attributed to remnants of the ancient perimeter wall that are still buried along the southern side of the mound. While no apparent correlation is found between the causes of tomb and ground movements, the crack pattern map supplements the overall structural assessment. The main outcome is that the northern portion of the retaining wall is classed with the highest hazard rate. The impact of this cost-effective approach is to inform the design of maintenance and restoration measures based on improved geognostic knowledge. The geophysical and surface evidence informs decisions on where interventions are to be prioritised and whether costly invasive investigations are needed

G/R 241 polymorphism of intercellular adhesion molecule 1 (ICAM-1) is associated with Fuchs uveitis

To investigate potential associations of the ICAM-1 gene polymorphisms and Fuchs uveitis in a cohort of Italian patients