Investigation of the Integrity of Subsoil as Foundation Support for a new Hostel Building, FUT, Akure, Southwestern Nigeria

Abstract

This research investigated the integrity of subsoil as foundation for a new building at the Federal University of Technology, Akure, Nigeria. All tests were carried out in accordance with the ASTM, AASHTO and Federal Ministry of Works and Housing standards. Eleven pits were dug while three samples were collected from top, middle and base layers of each pit totaling thirty-three. The results of natural moisture content (NMC) for the top layer averaged 14.7%, percentages of gravel, sand and fines averaged 26.9, 42.1 and 31.0 respectively, liquid limit (LL) 32.45%, plastic limit (PL) 23.8%, plasticity index (PI) 8.4%, linear shrinkage (LS) 8.4%, specific gravity 2.64, maximum dry density (MDD) 1582kg/m³ while optimum moisture content (OMC) averaged 22.7% and shear strength 24.5Kpa. The middle layer has average NMC of 22.37%, percentages of gravel, sand and fines 29.1, 36.4 and 34.5 respectively, LL 37.25%, PL is 24.9%, PI is 10.64%, LS 8.1%, specific gravity 2.66, MDD is 1638.9kg/m³ while the OMC is 20.73% and shear strength is 29.5kpa. Base layer has average NMC of 20.5%, percentages of gravel, sand and fines 24.6, 36.9 and 38.5 respectively, LL 37.6%, PL 25.1%, PI 12.38%, LS 7.3%, specific gravity 2.63, MDD 1768.7kg/m³ while the OMC is 18.7% and shear strength is 32.4kpa. % fines has a very strong positive correlation with LL, PL, PI, MDD, shear strength and UCS while it has a very strong negative with LS and OMC. It was observed that the top soil is non-critical considering the LL specification, while middle and base soils are intermediate. The inadequacy of the top and middle soils was noticed as a result of the non-compact state considering the bearing capacity and shear strength, while the base soil is characterized by fair MDD and high shear strength. Conclusively, the base layer is suitable as support for foundation.