Abstract
The Tunisian territory (area of diapirs) is exposed to the risks of ground movements linked to water, some of which are related to the phenomenon of dissolution of gypsum, allowing the appearance of underground cavities which present natural risks and set people in danger. The analysis of the hazard was determined by the field study coupled with the application of geophysical methods to locate and map the cavities and identify their dimensions and their positions in the subsoil. In the region of El Fahs (40 km NW of Tunis): we used a non-destructive method, georadar (GPR) with a 200 MHz antenna band-width, and an electric method, by using the electric tomography of which we have applicated the sequence of dipole-dipole measurement. The results ob-tained were examined and interpreted according to 2D profiles. The geophysi-cal methods of GPR and electrical tomography aim to detect many calvities in different depths. However, the geological radar was able to identify several cavities and the zones of dissolution whose investigation depth did not exceed the first 3 meters. On the contrary, the electric tomography method allowing the presence of several deeper underground cavities with larger dimensions ex-tended to 64 meters. To conclude, the geological and hydrogeological contexts of the terrain studied and on the state of the soil and subsoil allow us to better understanding the mechanisms of the establishment of the dissolution phe-nomenon and the appearance of cavities in the basement. The analysis of the predisposing factors present in the study area shows that the geodynamic con-text of the Triassic ascent takes place according to a precise thermodynamic process that favors the phenomenon of dissolution of the gypsum.
Highlights
Around the world, natural disasters linked to the presence of holes and the collapse of the ground are different and multiple, causing significant socio-economic damage
The Tunisian territory is exposed to the risks of ground movements linked to water, some of which are related to the phenomenon of dissolution of gypsum, allowing the appearance of underground cavities which present natural risks and set people in danger
The analysis of the predisposing factors present in the study area shows that the geodynamic context of the Triassic ascent takes place according to a precise thermodynamic process that favors the phenomenon of dissolution of the gypsum
Summary
Natural disasters linked to the presence of holes and the collapse of the ground are different and multiple, causing significant socio-economic damage. The Triassic in this area is characterized by generally evaporitic facies which will be exposed, in the presence of acidic water, to the phenomenon of dissolution of gypsum materials and the presence of numerous cavities and underground caves [6] The latter is susceptible to the collapse of the ground, which presents natural risks for the population and which can cause damage to infrastructure or buildings. The risk of soil collapse linked to the dissolution of gypsum is an unstable or dangerous situation requiring a decision and which must be resolved in these types of projects This natural phenomenon imposes more economical investment on developers, and even sometimes causes socio-economic damage. These techniques have given good results in recognition of the locality and the depth of certain underground cavities
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