Geotechnical, geochemical and mineralogical evaluations 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 indicated 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 suggested that the undesirable problem of swelling and shrinking of the soil when utilized for road construction will not be expected. The geochemical test result showed 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 SiO2, 17.56 wt.% of Al2O3, 9.03 wt. % of Fe2O3, 0.86 wt. % of TiO2 0.07 wt. % of P2O5 and less than 0.05% of CaO, MgO, K2O, MnO and Na2O. The oxides of silica, iron and aluminum help cement or bind the soil particles together. The results of geotechnical investigation showed 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/cm3 , optimum moisture content (OMC) of 18.99%, angle of internal friction (ɸ)of 12.15O , cohesion of 30.77 KN/M2 and coefficient of permeability of 1.24x10-3 mm/sec respectively. The Atterberg consistency limit showed 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. Based on the requirement of the Federal Ministry of Works and Housing, only a few of the soil samples satisfied the requirements for use as a sub-base material for the construction of roads. The undesirable soil samples that did not meet the requirement mentioned can be improved using suitable admixtures.