GEOTECHNICAL INVESTIGATION OF THE SUB-SOILS CONDITION AROUND YELWA NORTH CENTRAL PART OF NIGERIA FOR THE CONSTRUCTION OF INFRASTRUCTURES

Abstract

Investigation of the geotechnical conditions of the Sub-soils around Yelwa North Central part of Nigeria was carried out in order to know the possible causes of the infrastructural failures in the area. The investigation involves in-situ collection of the disturbed and undisturbed soil samples and were analysed in the laboratory based on British Standard (BS) method for soil testing for civil engineers. Results of the study reveals that; The Atterberg limit (Liquid limit ranged from 33.0%  to  43.0%, Plastic limits from 16.23% to 26.37%, Linear shrinkage  from 7.86%  to 15.71%, Plasticity index from  7.63%  to 24.77%). The Sieve analysis shows that; the percentage passing of the soil samples ranges from 31.62% to 67.60% which indicates poor materials. The Direct shear test revealed that the cohesive strength (c) ranges from 13 kN/m² to 24 kN/m², angle of internal friction (ø)° from 12° to 16° and unit weight (ϒ) from 18.17 kN/m³ to 20.87 kN/m³. From the Consolidation test; the Total settlement (Pc) ranges from 0.0008 m to 0.013 m, Coefficient of Consolidation (Cv) from 87.657 m²/yr to 109.325 m²/yr and Volume Compressibility (Mv) from 0.0048 kN/m² to 0.0205 kN/m². The Soil pH ranges from 6.4 to 7.4, Specific gravity (SG) from 2.57 to 2.73, and Natural Moisture Content (NMC) from 8.48% to 25.77%. The Compaction test revealed that; the Optimum Moisture Content (OMC) ranged from 13.22% to 20.60%, Maximum Dry Density (MDD) from 1.59 g/cm³ to 1.88 g/cm³which shows that the soil are mostly of silty-clay material and       Un-soaked value of California Bearing Ratio (CBR) ranges from 50.88% to 96.51%. The findings have revealed that, the sub-soil is characteristically fair to poor, and this required a form of geotechnics. Information acquired from the findings are expected to serve as guide in the choice of design and construction and as a baseline subsurface soil compendium for the construction of infrastructure in the study area and for further studies.