Geotechnical Risk Assessment and Geological Origin of Building Fracturation in Agadez City (North Niger)

Abstract

The Agadez city is built on the faulted and fractured sandstone formation of the “Agadez Sandstones”, which was deposited in unconformity on the Precambrian basement of the Aïr Mountain. The present study focuses on the geotechnical risk assessment and geological origin of building fracturation in Agadez city. A methodological approach integrating measurement of fractures planes affecting the buildings and their statistical analysis has been implemented. Statistical analysis of obtained data showed that in 100 fractured buildings, about 3% of buildings are at risk of collapse (very high risk), 64% of buildings are fractured (medium risk of collapse), and 34% of buildings are cracked (lower risk of collapse). These results showed as well that the nature of the material (rheology) influences the buildings fracturation. Indeed, buildings made from cement are more easily fractured than buildings made from clay materials. Statistical analysis of fracture planes reveals that the geotechnical risk associated with building's fracturation propagates in NW-SE, corresponding to the major directions of risk propagation, mainly dipping in northwest sectors (zones) of the Agadez city. The interpretation of geological and geophysical data combined with those obtained in the case of this study, reveals that the risk associated with buildings fracturation in Agadez city is caused by geological seismic events and or anthropogenic activities (explosive firing on the uranium mining sites like Somaïr and Cominak).