Geotechnical, Geochemical and Mineralogical Evaluation of Mine Spoils of the Jos- Bukuru Tin Field, Central Nigeria: Implications for Utilization as Road Construction Material.

The use of locally available and accessible soils for the construction of roads, has become necessary due to the high cost associated with the procurement of soils with good engineering features. A geotechnical, geochemical and mineralogical approach has been adopted to evaluate the mine spoils of the Jos – Bukuru tin field for road construction. X–ray diffraction analysis indicates that mineral phases in the soil are quartz (77.38%), kaolinite (18.70%), hematite (1.57%), rutile (0.42%), goethite (1.56%), gibbsite (0.31%), and a negligible amount of montmorillonite (0.06%) which suggests that the undesirable problem of swelling and shrinking of the soil when utilized for road construction will not be expected. The geochemical test result shows that the investigated soils based on the silica–sesquioxide ratio are residual soils that are not ‘’true laterites’’ and have an average composition of 71.81 wt. % of SiO 2 , 17.56 wt.% of Al 2 O 3 , 9.03 wt. % of Fe 2 O 3 , 0.86 wt. % of TiO 2 0.07 wt. % of P 2 O 5 and less than 0.05% of CaO, MgO, K 2 O, MnO and Na 2 O. The oxides of silica, iron and aluminum help in cementing or binding the soil particles together. The results of geotechnical investigation show that the soils are poorly graded with an average fine (silt and clay) composition of 56.03%, California bearing ratio (CBR) of 34.64%, maximum dry density (MDD) of 1.65g/cm 3 , optimum moisture content (OMC) of 18.99%, angle of internal friction (ɸ) of 12.15 O , cohesion of 30.77 KN/M 2 and coefficient of permeability of 1.24x10 − 3 mm/sec respectively. The Atterberg consistency limit shows that the liquid limit, plastic limit, plasticity index and linear shrinkage values have averages of 38.68%, 23.16%, 15.53% and 10.33% respectively. This investigation revealed that the soils can be utilized as subgrade in road construction and as sub-base only when adequately compacted. This is due to the high percentage of fines and plasticities of the soil.