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/cm3 which 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.