Effect of pocketing pillar — A numerical and laboratory study

Coal pillars are the main support element for underground coalmines. If pillars are under-designed, significant safety, production and operational hazards would be produced. 15 major collapses have occurred in NSW and Queensland in the last 10 years. Over 12 people have been killed and over $10,000,000 of surface damage sustained; or if pillars are over-designed, resources would be wasted and productivity would be jeopardised. Although there are empirical formulae ready to use for regular shaped pillars (square pillars), there are still deficiencies in the methods used to estimate the strength of irregular shaped pillars, such as the irregular pillars caused by pocketing operations, which are sometimes encountered in Australian mining operations. As a result of this, some unplanned pillar failures have occurred. The purpose of this research was to investigate the strength of irregular pillars caused by pocketing in relation to square pillars. It is found that pocketing in pillar produces no noteworthy PCFS reduction when pillar starts yielding. However, it does significantly reduce PRFS accordingly with the pillar mechanical property. It seams that the friction has little influences on PRFS.