Geotechnical characterization of the quaternary alluvial deposits in Tunis City (Tunisia)

• Evaluation and mapping of the spatial variability of geotechnical parameters.
• In situ testing are helpful for mechanical parameters identifications.
• Quaternary alluvial characterization for safe urban extension.
• Geotechnical characterization of the underground horizons.

Tunis City is always in perpetual extension. The urban extension takes place in areas covered by quaternary alluvium. To evaluate the spatial variability of geotechnical parameters, 190 boreholes and in situ tests, across the quaternary deposits, were selected with a series of physical properties and mechanical parameters. To accomplish this research, the adopted approach was divided into four steps: (1) data collection; (2) geotechnical data georeferencing; (3) interpolation methods and (4) establishment of maps showing the spatial variability of the geotechnical parameters. Results of this study show that the quaternary deposits provide high water infiltration capacity and form the main aquifer of the study area. The low topography in Tunis City emphasizes the problem of flooding. The presence of sensitive clay causes a swelling–shrinkage behavior of the soil if the clay is dry. The disorders and damages caused by the swelling clay are especially located in the Ksar-Said Bardo–Mannouba, in Bab Saadoun, in the eastern part of Sebket Essijoumi and in the southwestern side of Tunis lagoon. On the other hand, in situ tests show that quaternary deposits contain strong shallow foundation level and vary from 0 to 5 m of thickness. These levels are made up by sand, tuff and hard clay. Muddy soils, in the Tunis City and its surrounding area, have a poor geotechnical characteristics and cause differential and absolute risk of settlement. The good bedrock in these locations is defined by muddy and sand levels and it exceed 60 m of depth. The existence of a higher concentration of gypsum causes local disorders such as the Henchir El Yahoudia site.