Detection of karst features and associated geohazard using ground penetrating radar and 2D electrical resistivity imaging; case study from Sannur protectorate, Egypt
The current work explores the suitability and advantages of utilizing ground penetrating radar (GPR), and electrical resistivity imaging (ERI) in the hazard assessment process of Sannur cave associated with water inrush, structural instability, and engineering uncertainty in the site. The huge cave was discovered during mining of alabaster stone in the Egyptian Eastern Desert and considered a karst feature hosted in Eocene limestone with a several types of speleothems. The area is well-known for its high degree of karstification due to a long period of water erosion and the development of fractures network. Detailed geological and geophysical studies, including geological mapping of the area, 3D laser scan, fracture trend analysis, 2D GPR, and 2D ERI has been carried out to study the suitability of the site for safe touristic activities. GPR data delineated numerous probable cavities and fractures (fissures) within limestone formation due to karstification processes below the road heading down to the cave conformable to those analysed fractures exposed at the surface. The integration of GPR and ERI data in the yard outside the cave opening shows good correlation in the determination of lithostratigraphic sequence and dimensions of two electrically conductive clay lenses in addition to inferred fractures striking NW‒SE conformable with outcrop studies of fractures in the vicinity of the cave. Recommendations were proposed to be taken into consideration for preparing the site and the results encourage the integrated application of such geophysical techniques for the reconnaissance and further detailed characterization of the karst features within the area.