Geotechnical Assessment of Slope Stability in Open-Pit Coal Mines in Benue State, North Central Nigeria

Open-pit coal mining operations in Benue State, North Central Nigeria, are associated with recurrent slope failures that endanger workers and disrupt production. This study conducts a geotechnical assessment of slope stability conditions at selected open-pit coal mines in Benue State. Field mapping of geological structures, including joints, faults, and bedding planes, was carried out using a Brunton compass. In-situ rock quality designation (RQD) measurements and laboratory testing of shear strength parameters on collected rock core and soil samples were performed. Slope stability analyses were undertaken using the limit equilibrium method with Bishop's simplified circular failure criterion in RocScience Slide2 software. Results identify planar and wedge failure modes as dominant instability mechanisms, governed principally by the orientation of bedding planes relative to slope faces. Factor of safety values below 1.2 were calculated for several existing bench configurations. The study recommends slope geometry redesign incorporating reduced bench heights, installation of catch berms, and dewatering of pit walls through horizontal drains to reduce pore water pressure. Regular geotechnical monitoring using slope inclinometers and survey prisms is also advocated. These findings provide practical guidance for mine planning engineers at Benue coal operations and contribute to national documentation of geotechnical hazards in Nigerian coalfields. Keywords: slope stability, open-pit mining, Benue State, geotechnical, coal mining.