THREE-DIMENSIONAL NUMERICAL MODELLING OF A TWO-UNIT COAL MINE PANEL FOR PROPOSED ROOM AND PILLAR MINING, OKABA, KOGI STATE

Abstract

This research focused on the design of a two-unit coal mine panel using RS3 geotechnical software. The underground room and pillar mining system is proposed to avoid the high stripping cost involved in removing the constantly increasing overburden required to gain access to the coal seam existing behind the current excavation face. Representative samples for each lithologic unit were collected from the Okaba coal mine and laboratory test was carried out to determine their geotechnical properties. The values of these properties were used as input parameters for the numerical model, together with the average thickness of 16 m, 36 m and 2.6 m for laterite, shale and coal respectively. The two-unit coal mine panel was developed in four stages and the result for maximum principal effective stress, total displacement, maximum shear strain and the strength factor model was computed and analysed. The average densities for laterite, shale and coal samples were 1.94 g/cm³, 2.16 g/cm³ and 1.07 g/cm³ respectively. The cohesion, angle of internal friction and tensile strength for laterite were 50.2 kPa, 32.7º and 0.059 MPa; that of shale were 208 kPa, 31.6º, and 3.27 MPa; and that of coal were 231.7 kPa, 27.5º and 3.39 MPa respectively. The UCS, Young’s modulus and Poisson ratio were for laterite 0.24 MPa, 0.11 GPa and 0.32; that of shale were 3.2 MPa, 1.2 GPa and 0.3; and that of coal were 1.242 MPa, 0.52 GPa and 0.27 respectively. The result of the analysis showed a maximum principal effective stress of 5295.71 kPa, a maximum total displacement of 0.019 m, a maximum shear strain of 0.0048 and a strength factor of 0.88. These parameters showed a high correlation at similar locations in the numerical model and attained their highest values at the centre of the developed mine panel. It was recommended that an immediate extraction could begin using the room and pillar mine plan as portrayed in the numerical model and that the excavation should be adequately supported at the centre of the excavated mine panels.