Pillar stability analysis for partial pillar extraction. A case study at an underground coal mine in southern Africa

This paper investigates the applicability and operational characteristics of different partial pillar extraction methods for a room-and-pillar coal mining project located in the region of southern Africa. Three partial pillar extraction methods, i.e. the Pillar Splitting method, the Duncan method and the Lift Left-Right method are evaluated using three-dimensional finite element analysis. Multiple 3D models were developed for each method by varying the geometry of the remnant pillar during partial pillar extraction. Pillar strength was estimated using the Salamon and Munro equation and pillar stress was obtained from the numerical models. Surface subsidence was also calculated for each room-and-pillar panel. All three methods meet the stability factor requirement for safe secondary extraction. The Lift Left-Right method exhibits the highest stability factor while the Pillar Splitting method is the most favorable in terms of surface subsidence.