INVESTIGATING THE INTEGRITY OF THE SUBSOIL AS FOUNDATION SUPPORT MATERIALS FOR A HOSTEL BUILDING, FUTA, SW, NIGERIA

The integrity of subsoil as foundation support material for a hostel building at the Federal University of Technology, Akure, Nigeria was investigated. All tests were carried out in accordance with the ASTM, AASHTO and Federal Ministry of Works and Housing standards. Thirty-three samples were collected from top, middle and base layers of eleven pits. The results of natural moisture content (NMC) for top, middle and base layers averaged 14.7%, 22.37% and 20.5% respectively. Gravel percentages averaged 26.9, 29.1 and 24.6; sand 42.1, 36.4, 36.9; and fines 31.0, 34.5 and 38.5 respectively. The liquid limit (LL) values are 32.45%, 37.25%, 37.6%; plastic limit (PL) 23.8%, 24.9% and 25.1%; plasticity index (PI) 8.4%, 10.64% and 12.38%; linear shrinkage (LS) 8.4%, 8.1% and 7.3%; specific gravity 2.64, 2.66 and 2.63; maximum dry density (MDD) 1582kg/m³, 1638.9kg/m³ and 1768.7kg/m³; optimum moisture content (OMC) 22.7%, 20.73% and 18.7%; and shear strength 24.5Kpa, 29.5kpa and 32.4kpa respectively. A very strong positive correlation exists between % fines and LL, PL, PI, MDD, shear strength and UCS with a very strong negative existing between %fines and LS and OMC. It was observed that the top soil is critical considering the geotechnical parameters, while middle and base soils are marginal. The soils of the top and middle layers are non-compact in tandem with the lower bearing capacity and shear strength, while the base soil is characterized by a higher bearing capacity and shear strength. Conclusively, with a little treatment, the base layer is suitable as support for the foundation.