GEOTECHNICAL CHARACTERIZATION OF SOILS AND SOME SELECTED ROCK TYPES IN AKURE, SOUTH WESTERN NIGERIA FOR ENGINEERING APPLICATIONS

Abstract

A variety of twenty soil samples (SLN1-SLN20) and ten rock samples were selected for the study in Akure metropolis. The rocks were studied for their characteristics, petrography and Uniaxial compressive strength. The soil samples were testedfor Natural moisture content, Specific gravity, Particle size distribution, Atterberg limits, Compaction and Uniaxial compressive strength and shear strength. The result of the petrographical studies shows that micro cracks, cleavages and undullose extinction, which are evidence of stress characteristics the petrography of the Charnockitic rock. Other rock types exhibit various degrees of microstructures. The UCS of Charnockitic rocks, Quartzite and Porphyritic granite are believed to have been lowered by the textural and petrographic characteristics. The textural and micro structural characteristics have more influence on the UCS of the rocks. It was further discovered that micro structural and textural characteristics influenced the UCS of rocks more than the mineral content and incipient weathering. It was observed from the geotechnical tests that the moisture content of the soils samples ranges from 8.75% to 28.5%. The moisture content of the soil samples was influenced by seasonal change, clay content, organic content and drainage condition. The liquid limit value ranges from 23.5% to 60.4% and the plastic limit value ranges from 15.8% o 36.2% and the plasticity index values were low, medium and high from all the samples. The specific gravity value for the soil samples fall within the reported specific gravity value for lateritic soils of 2.5-4.6. The compaction test conducted on the soil samples shows optimum moisture content value ranges from 15.3% to 36.8% while the maximum dry density value is between 1366kg/m3 and 1831kg/m3 From the results obtained, it was revealed that rocks with coarse texture are of lower UCS values of less than 20MPa and also discovered that weathering decreased the UCS value. Based on these discoveries, rocks with coarse texture and evidence of weathering should be avoided in engineering construction process. Samples from locations SLN3, SLN9, SLN10, and SLN14 have a low swelling potential therefore are good for construction purpose. Samples from locations SLN2, SLN4, SLN8, SLN11, SLN13, SLN15, SLN16, SLN18, SLN19 and SLN20 are expected to have medium swelling potentials so such soils can be treated if want to be used as sub grade and base materials while sample from locations SLN1, SLN5, SLN7, SLN12 and SLN17 are expected to have high swelling materials showing that soil samples in these areas are problematic.