Stability study of coal pillars due to induced stress driven spalling during development and mechanised depillaring at different depths of cover

Induced stress driven spalling in coal pillars depends on several factors including depth of cover, in-situ stresses and presence of weak planes. A solid coal pillar generally experiences spalling at a higher depth. Fender and snook/rib experiences considerable spalling during depillaring even at lower depth below strong and massive rock mass. The spalling in pillars leads to instability at working places including goaf encroachment during depillaring. This paper discusses the measurement of induced stress driven spalling during development of a seam having weak roof-pillar interface at 850-900 m at CSM mine in Czech Republic. Spalling is also examined in different form of coal pillars during mechanized depillaring at 250 m depth at Godavarikhani 11 Incline mine in India. Finite difference based numerical modelling was carried out to assess the behaviour of the pillars. Ultimate non-elastic region was observed up to 9 m near the roof-pillar interface due to presence of weak plane and around 8 m at middle height of the pillar at the higher depth. At the moderate depth of around 250 m, maximum vertical induced stress was observed over a fender. Spalling of 2 m and 1.5 m was observed in the fender and pillar respectively.