Geotechnical Evaluation of Soils in Numan and Its Environs , North East Nigeria

A geotechnical evaluation of some soils in Numan, Adamawa, North –East, Nigeria has been carried out. This was done to determine the suitability of the soils for use as subgrade/filling, sub-base and base course materials for road construction. The samples were collected from five different areas, at surface and sub-surface levels. The areas are New Demsa, Farei, Dowaya, Numan Town and Imbru. The soil samples were subjected to laboratory investigations in conformity with the American Association of State Highway and Transportation (AASHTO) and the Bristish Standard Institution (BSI) Standard specifications. Results of the geotechnical tests indicate that the proportion passing the BS sieve NO.200 ranges from 20. 92% to 39. 02% whereas plasticity index and consistency index ranges from 14.05 to 22. 01 and 1. 42% to 2. 16% respectively. The compaction test result revealed an optimum Moisture Content (O.M.C) Value of 11. 60% and a maximum Dry Density (M.D.D) Value ranging from 91g/cm 2.08g/cm The California Bearing Ratio Values ranges from of 8% to 24%, whereas the plastic limit values ranges from 30% to 51%. Soils at New Demsa, Farei, Numan Town and Imbru are thus considered suitable for use as sub-grade/filling materials, while the soil at Dowaya is unsuitable for use as subgrade/filling and sub-base material. This is probably why the road at this area failed after construction.