Determination and establishment of empirical relationship between magnetic susceptibility and mechanical properties of typical basement rocks in Southwestern Nigeria

Abstract

Magnetic susceptibility and mechanical properties of rocks in a typical basement complex Southwestern Nigeria were correlated with the aim of establishing empirical equations relating the two parameters and evaluate the parameters as related to its competency in hosting civil structures. A total of thirty rock samples were taken across the geology of the area and subjected to mechanical properties determinations. Magnetic susceptibility measurements were carried out on in-situ fresh rock outcrops and it ranges from 2.1 × 10-4 to 9.5 × 10-4. This signifies the amount of iron content in the rocks and its level of induration. The values of uniaxial compressive strength (UCS), Young’s modulus (E), shear modulus (µ), bulk modulus (K) and Poisson’s ratio (Ѵ) ranges 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 the magnetic susceptibility exhibit a direct linear relationship. The relationship shows a good correlation with coefficient of correlation (R) ranging from 0.60 to 0.85 for uniaxial compressive strength, bulk modulus and Poisson’s ratio. The magnetic susceptibility relationship with shear and Young’s Modulus are relatively weak with coeffecient of correlation (R) of 0.44 and 0.47, respectively. This implies that, magnetic susceptibility measurement may not be reliably applicable in determination of the stiffness of rocks and the rate of resistance of rocks to prevailing shearing loads. The validation results show that, reliable mechanical properties of rocks can be estimated from magnetic susceptibility measurements using the established empirical equations. Key words: Magnetic, susceptibility, mechanical, properties, rocks.