Localization and shape determination of a hidden corridor in the Great Pyramid of Giza using non-destructive testing.

Built over 4500 years ago, the Great Pyramid of Giza, Egypt, is the only remaining structure of the Wonders of the Ancient World as described by the ancient Greek historian Herodotus. Despite this long existence, only recently has modern science and technology been employed to study this massive stone structure. Cosmic-ray muon radiography throughout the ScanPyramids project has detected a large void above the Grand Gallery of the Great Pyramid and a smaller unidentified void behind the so-called Chevron. The Chevron is an assembly of four large limestone blocks arranged in the shape of two inverted downward open angles. Guided by the muon results, the ScanPyramids teams from Cairo University (Egypt) and the Technical University of Munich (Germany) have carried out three measurement campaigns between 2020 and 2022 to characterize the pyramid's stone at the Chevron and confirm the presence of the ScanPyramids North-Face Corridor (SP-NFC) by employing a range of Non-Destructive Testing (NDT) techniques. This paper presents selected results from Ground Penetrating Radar (GPR) and Ultrasonic Testing (UST) measurements that were deployed to the surface of the Chevron. To support the NDT interpretation and to validate the gathered results, numerical simulations in 2D and 3D for GPR and UST were performed. Additionally, Image Fusion (IF) was used to combine the reconstructed GPR and UST images, allowing for a more informed interpretation and confirmation of features observed in the individual images. This work confirmed that behind the blocks of the Chevron lies a strong air anomaly that can be associated with the SP-NFC predicted with cosmic-ray muon radiography. In addition to providing proof of the existence of the corridor, the multi-modal NDT approach enabled the precise localization of the corridor and the determination of its geometry. Based on these findings, the ScanPyramids team will propose the coordinates for a small-diameter borehole, which will, for the first time, provide direct access to the hidden corridor and allow its inspection. [ABSTRACT FROM AUTHOR]