Analysis of Ground Control Hazards in Underground Limestone Mines in South West Nigeria

Underground limestone mining using room-and-pillar extraction methods in South West Nigeria presents distinct ground control hazards that require systematic management to prevent fatal roof falls and pillar failures. This study analyses ground control conditions and hazard management practices at underground limestone operations in Ondo and Ekiti states. Geotechnical characterisation was conducted at four underground mine sites, including mapping of joint sets, measurement of pillar dimensions, and assessment of roof span conditions using the Stability Graph method. Rock mass quality was classified using the Rock Mass Rating and Q-system. Historical ground control incident records were reviewed, and interviews were conducted with mine managers and underground workers. Findings indicate that pillar width-to-height ratios at two of the four mines are below the minimum recommended values for the prevailing rock strengths, indicating inadequate factor of safety against pillar collapse. Roof spans in several rooms exceed safe limits for the measured rock quality, with unmaintained support systems at two operations. Ground control incidents, including minor falls and rib spalling, occur at an average rate of 2.4 per month across the study sites. The study develops site-specific pillar design recommendations and safe roof span tables for each operation and recommends mandatory ground control management plans as a licensing condition for underground mines. Keywords: ground control, underground limestone mining, South West Nigeria, pillar design, roof stability.