The current research discusses the validity of utilizing Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) for the geo-hazard assessment and the detection of the subsurface voids associated with mining activities. The presence of subsurface voids poses a significant safety challenge to any operating mine due to the associated geotechnical risks and the severe consequences for human life, the environment, and mine infrastructure if left unaddressed. Traditional subsurface investigation tools in mines are borehole and probe drilling, which are costly, time-consuming, and unable to provide a comprehensive image of subsurface structures. In contrast, geophysical techniques have demonstrated through decades of research their exceptional ability to obtain a complete subsurface image, surpassing other invasive methods. In this case study, a geophysical survey was conducted at the actively operating Sukari gold mine (SGM) in Egypt utilizing a combination of GPR and ERT to detect unknown subsurface voids. Based on the joint interpretation of both techniques, risk zones were identified and delineated. Moreover, the obtained results were validated through numerical simulations and existing borehole data. This study demonstrates the efficiency of integrating geophysical techniques with geological and mining information in active mines to enhance operational safety by minimizing the risks of subsurface subsidence and failure in a timely/cost-effective way. Additionally, It represents the first published work on identifying subsurface voids in a large-scale operating gold mine in Egypt utilizing near-surface geophysical techniques.

Sorghatmesh mosque is a historical structure that was constructed in Cairo, Egypt, by Prince Saif El-Din Sorghatmesh in 1356. A dual-frequency ground-penetrating radar (GPR) with 250–700 MHz was used to investigate the subsurface of the Sorghatmesh mosque for restoration purposes. A total of 37 lines were surveyed on the ground floor of the mosque. The subsurface utilities were detected, and the status of the concrete base and the medium of the ground floor were assessed. A set of subsurface anomalies were detected and interpreted within the ground floor area of the mosque. In order to validate the interpretation, a trial pit was drilled on the ground floor, allowing for the visual inspection of the subsurface, and a Georadar numerical simulation was carried out to study the responses of the subsurface materials and conditions. For a better comprehension of the results, the ground floor area was categorized into five zones where the GPR interpretations between survey lines are almost similar. This work not only demonstrates the effectiveness of GPR as a non-invasive investigation tool but also highlights the potential of integrating advanced technologies into cultural heritage preservation by offering refined methodologies and insights for future research and restoration efforts.

The application of Electrical Resistivity Tomography (ERT) for the investigation of architectural heritage has numerous limitations. In most cases, we are referring to historic stone buildings and monuments built from limestone, sandstone, or granite blocks, where many features may complicate the interpretation of electrical resistivity data. First of all, there is incomplete or missing information about principles of building construction and the materials used. Another challenge is the heterogeneity of the masonry as a material due to the presence of many joints between the stone blocks, which may be filled with cementitious materials or be completely or partially empty. For medium-scale studies with limited penetration depth, the presence of air in the joints between stone blocks may affect the electrical resistivity distribution and interfere with the detection of the archaeologically relevant anomalies associated, in particular, with the presence of air cavities. Systematic studies of the applicability of the Electrical Resistivity Tomography in such blocky structures are lacking. In this study, the effect caused by masonry geometry was assessed using numerical 3D modelling of the electrical resistivity distribution in a simplified blocky structure consisting of rows of masonry blocks by incorporating joints between them. The purpose is to study how the presence of air-filled joints affects the ability of the ERT method to detect voids in masonry structures depending on the position and size of these voids. The analysis of numerical models provides insights to facilitate the interpretation of ERT results in historical monuments and other structures constructed from stone blocks.