GEOTECHNICAL EVALUATION OF SOILS IN NUMAN AND ITS ENVIRONS, NORTH EAST NIGERIA (original) (raw)

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 sub-grade/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 3 2.08g/cm 3 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 sub-grade/filling and sub-base material. This is probably why the road at this area failed after construction. BACK GROUND INTRODUCTION In highway design and construction, careful attention is not only given to sampling and testing of the aggregates which are required to provide a pavement that will be sound and durable; but also to the subsoil materials which will provide support for the pavement (Okagbue and Uma, 1988). In selecting the route for the highway, one of the important factors considered is the geotechnics of the subsoil. At least a casual study of the subsoil through which the highway must pass is exceedingly helpful. From it the general stability of the area can be determined. Furthermore experience has shown that subsoil conditions along a highway route can be a crucial factor in the serviceability and good performance of the highway (Weinert ,1968; Earquhar, 1980). It is therefore very crucial to determine the geotechnical properties of soils in order to establish whether a particular soil is suitable for use as fill, grade or sub-base materials. Some of the roads in Numan area have failed and hence constitute potential hazard to pedestrian and motorists alike because of lack of informed geotechnical data on the sub soil conditions. Most of the previous work done in the study area are mainly regional (Falconer, 1911) and have described the geology of the Upper Benue Trough in terms of sedimentary and stratigraphic aspects. Subsequently, (Carter et al, 1963) gave some details on the geology, geological structure, hydrology and water quality of the old Northern Nigeria in which the study area is included. Offodile (1976) wrote on the origin of the Benue Trough and Geology of the cretaceous of the valley. Braide (1992) studied the sedimentation and tectonics of the Yola arm of the Benue Trough with emphasis on facies architecture and their provenance significance. Offodile (1976), also gave some details on the sedimentation, tectonics and hydrolithological characteristics of part of the Benue Trough. Head (1988) indicated the various methods to be employed in the treatment of expansive soils and gave out the procedure to be adopted in the laboratory. Obiefuna et al., (1999), gave detailed account of the geological and geotechnical evaluation of selected gully sites in Yola area of Adamawa, north–east, Nigeria and recommended on how to tackle the environmental hazards.