Physicochimical,mineralogicaland Geotechnicalcharacterization of the Earth of the 9th District of the City of Ndjamena in Chad With a View to the Construction of Hydraulic Structures

The work carried out in this paper aims at the physicochimical, mineralogical and geotechnical characterization of the soils used in the construction of dikes in the 9th district of the city of NDjamena in Chad in order to guide those responsible for the construction of structures related to this soil.Physicochimical,mineralogical and geotechnical analyses were conducted. The results obtained show that the soils used for the construction of the dikes (existing structure is a dam made of earth without a coating at the time) are fine soils with a percentage of the fines that varies between 38.7% and 73.1% at the 80μm screen. According to the GTR classification, these floors belong to classes A2 and A3.The plasticity index of the soils studied ranges from 18 to 35. These values confirm that the soils used are plastic soils. The porosity is in the range of 34.23% to 40% and the void index is between 0.36 and 0.59. These soils are very sensitive to water, compaction and deformation.Chemical analysis shows us that Silicon oxide is the most dominant constituent (63.29% to 80.22%) followed by Aluminum oxide (10.49% to 18.15%) and iron oxide (3.22% to 5.87%).Mineralogical analysis confirms that Quartz is dominant (56.24% to 46.5%) followed by Kaolinite (27.41% to 12.07%), illite (12.38% to 9.43%), k-feldspar, plagioclase and other minerals. The presence of smectite shows that the soils are made up of clays that have a high swelling capacity. Thus, the use of these soils in hydraulic structures such as dikes and dams requires special treatment so that it can effectively perform their roles.