Geological-geomechanical setting for the stability analysis of the rock hewn churches of lalibela (Ethiopia)

This paper deals with the geomechanical characterization of the Lalibela (Ethiopia) rock-mass within which the famous UNESCO cultural heritage hewn churcheswere excavated. The churcheswere excavated into a layer of ignimbrite embedded between basalts flows. On the base of a detailed field survey, geological and geomechanical data were collected in order to perform experimental stability analysis (by a FEM code) on one of the hewn churches (Biet Gabriel Rufael church). For this purpose, the church has been considered as a rock-mass excavated for a quarry or mining site. Due to the high seismicity of the near Ethiopian Rift, stability analysis also took into account the seismic input, according to the indication of Eurocode 7 and Italian rule NTC 2008. The results of the experimental FEM stability analysis points in favor of a positive verification for the stability of the Biet Gabriel Rufael church even in the event of input from the expected earthquake in the Ethiopian Rift. In presence of interest, this positive result can be applied to all the hewn churches of Lalibela.