Rock mass quality and preliminary analysis of the stability of ancient rock-cut Theban tombs at Sheikh ‘Abd el-Qurna, Egypt

The ancient Theban tombs at the hillside cemetery of Sheikh ‘Abd el-Qurna (SAQ), west of Luxor, Egypt, were excavated mainly in the Thebes Limestone Formation and show varying degrees of damage of rock pillars and ceilings. In order to understand the rock mass behaviour in selected tombs and its impact on past failures and current stability, we carried out geological mapping and rock mass quality assessments. Our work provides a geological map and geotechnical evaluation of the rock mass of these SAQ tombs and their surroundings. We mapped and described rock fractures in situ and with remote sensing data, and estimated the rock mass quality of the different members within the Thebes Limestone Formation using the Rock Mass Rating (RMR) and Geological Strength Index (GSI) systems. In addition, we conducted a rock pillar analysis. Analyses and mapping were supported by new high-resolution terrain models computed from ground-based and aerial photogrammetry and from terrestrial laser scanning. Our analyses show that the tombs at SAQ have been cut into poor to very good quality rock masses. Rock failures of ceilings and pillars were frequently facilitated by local, unfavourably oriented persistent discontinuities, such as tension cracks and faults. Other failures were related to the disintegration of nodular limestone into individual nodules upon weathering. Our data suggest that, in 18th Dynasty monumental tomb construction, low-strength rock masses rarely resulted in modifications of the planned tomb design in order to minimise the risk of rock falls and collapses.