Empirical Relationship between Gravimetric and Mechanical Properties of Basement Rocks in Ado-Ekiti, Southwestern Nigeria

Abstract

Gravimetric and mechanical parameters of Basement rocks in Ado-Ekiti, South-western Nigeria were correlated for engineering foundation studies with the aim of establishing an empirical relationship between the two parameters. Field operations revealed Charnockite, Migmatite, Granite Gneiss and Quartzite as principal basement rocks in the study area. Fresh rock samples were taken from thirty (30) locations cutting across the geology of the study area. Simple pendulum principle and Archimede’s principles were employed to determine the gravity and the specific gravity of the rock specimens repectively. The mechanical analyses (uniaxial compressive strength, shear strength, Young’s modulus, Bulk modulus and Poisson’s ratio) for the thirty rock samples were determined employing standard method. This is applicable to all engineering foundation studies to determine the compence of such areas for engineering developments. The engineering studies revealed the reliability, stiffness, soundness and resistance of the subsurface rocks to the prevailing overhead loads. The results indicated that the gravity and specific gravity values ranged from 935055.46 mgal to 1038167.647 mgal and 2.61 to 2.83 respectively. The values of Uniaxial Compressive Strength (UCS), Young’s modulus (E), Shear modulus (μ), Bulk modulus (K) and Poisson’s ratio (N´) ranged from 49–107 mpa, 1003–3321 mpa, 416–1310 mpa,707–2728 mpa and 0.232-0.316 respectively. The cross plots of the mechanical parameters with gravity and specific gravity showed good correlation with coefficient of correlation (R) ranging from 0.52 to 0.84 and 0.52 to 0.81 respectively. Results validation exercise also indicated that some of the Uniaxial Compressive Strength and Poisson’s ratio have good representation in the derived empirical equation with the two geophysical parameters in this study. The established relationship between the gravimetric and the mechanical parameters revealed that; the mechanical strength of rock is a function of the gravitational pull effect on the rocks and that migmatitic and granitic rocks possessed more mechanical strength than the gneissic and quarzitic rocks that characterised the study area. Some of the equations generated has been found reliable and useful in the determination of the mechanical properties. The physical methods adopted being faster, cheaper, proven and more comprehensive would solve some engineering problems in examining the engineering properties of these basement rocks related terrains.