Application of the yield pillar technique for successful depillaring under stiff strata

Abstract Related in this paper is a case study of double-section contiguous depillaring of a 12.6 m thick coal seam under massive and uncaveable sandstones. Drilling results indicate the sandstones to be 20–55 m thick with high RQD values. Depillaring has been so far completed in five extraction panels, leaving properly designed yield pillars in the goaf for prevention of air blasts. The paper gives the design procedure adopted for yield pillars and the results of long-term pillar displacement monitoring.