Stability analyses of bleeder pillars in longwall mines by displacement-discontinuity method

Caving in coal mines releases significant amounts of dust and gas. This is exhausted from the mine by forcing the air to travel through the caved zones into a set of roadways known as bleeders. These bleeder entries are operated for the life of the mine, and therefore, they have to be kept in stable condition. Caving operations in coal mines are associated with longwall mines and complete pillar extraction. The pillars adjoining the caved zone sometimes show rib failures, posing a hazard for mine personnel travelling through the entry. In this paper, we present the results from analyses of bleeder pillars that are near the caved zones and are susceptible to damage because of the transfer of load during the caving process. In this study, bleeder pillars were simulated in a displacement discontinuity program. Results showed that the vertical stresses on bleeder pillars increased while the safety factor of bleeder pillar decreased during the caving process; however, when the caved zone completely consolidated, both the stresses and safety factor did not change for the remaining extraction. When similar extraction was performed at deeper depths, vertical stress on pillars increased significantly.