TITLE:
Geophysical Investigation of the Triassic Salt Material Hazard: El Fahs Case Example (Northern Tunisia)
AUTHORS:
Mohamed Khaled Bouzid, Adel Klai, Romdhane Haddad, Mohamed Chedly Rabia
KEYWORDS:
Triassic Materials, Natural Hazards, Underground Cavities, Thermodynamic Process, GPR, Electric Tomography
JOURNAL NAME:
International Journal of Geosciences,
Vol.11 No.11,
November
9,
2020
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.