Geotechnical Characterization Of Borrow Materials For Unpaved Roads In Niger: Case Studies From The Tahoua And Agadez Regions.

In most developing countries, particularly Niger, unpaved roads account for more than 70% of the national road network. Their widespread use is justified by the availability of construction and maintenance materials in the immediate vicinity of project sites. However, these roads have limited durability because of the characteristics of the borrow materials used and the unsealed nature of the roadway. This study assessed the suitability of these borrow materials for the construction and maintenance of unpaved roads through laboratory testing, including particle-size analysis, Atterberg limits, Proctor compaction tests, and CBR tests. The results show Class B and C1A1 soils, with liquid limit values generally consistent the recommendations of the CEBTP guide. However, the plasticity index values for 14 of the 15 soil samples are below the CEBTP recommendations. Regarding CBR, only 3 of the 15 samples yielded values below 30, which is below the recommended threshold for traffic volumes exceeding 30 vehicles per day. This study highlights the significant potential of local materials for the construction of earthen roads in Tahoua and Agadez regions. However, their optimal use requires improvement measures to ensure the stability, durability, and performance of the road infrastructure, as discussed below.