Empirical Study of Rock Mechanics Parameters Influencing Underground Mine Design at Coal Deposits in Kogi State

Reliable rock mechanics data are fundamental to safe and cost-effective underground mine design, yet the coal-bearing sequences in Kogi State, North Central Nigeria, have not been characterised by systematic laboratory testing and in-situ measurement in recent studies. This study empirically characterises rock mechanics parameters relevant to underground mine design at coal deposits in the Shintaku and Ogboyaga fields of Kogi State. Laboratory testing was conducted on core samples from four diamond drill holes, measuring uniaxial compressive strength, indirect tensile strength (Brazilian test), Young's modulus, Poisson's ratio, and triaxial shear strength parameters using ISRM suggested methods. In-situ stress measurements were made using hydraulic fracturing at two borehole locations. Geomechanical classification using the Coal Mine Roof Rating system was applied to logged core intervals. Results indicate that immediate roof sequences are predominantly weak mudstone and shale with uniaxial compressive strength averaging 22 megapascals, classifying as poor to fair quality in the CMRR system. In-situ horizontal stress magnitudes are 1.8 times vertical stress, indicating a high horizontal stress environment with implications for entry stability. Coal seam strength averages 15 megapascals, below values typically relied upon for pillar design. The study provides calibrated empirical design inputs for room-and-pillar mining and recommends a mechanised longwall feasibility assessment for the deeper sections of the Shintaku field. Keywords: rock mechanics, underground coal mining, Kogi State, mine design, geomechanics.