User:ABOOBAKR AMIRI

ABSTRACT Pillar is an area of coal left to support the overlying strata in a mine, they are crucial for the stability of pillar supported mining methods in general and specifically for coal mine in Bord and Pillar mining method, in the development stage and depilating stage. In mining, the loading environment on pillars is highly complex with a combination of normal and shear stresses. It is also known that with an active working face, constant redistribution of stresses will occur to maintain stress equilibrium. Bord and Pillar's mining is the oldest mining method of coal deposits, and this method is still being used for recovery of coal from underground mines, due to its simplicity in the excavation method, good safety measures, and ventilation. The key to successful Bord and Pillar Mining is selecting the optimum pillar size and stability of the pillar. If the pillars are too small the mine will collapse. If the pillars are too large then significant quantities of valuable material will be left behind reducing the profitability of the mine. Historically, coal pillar design has been based on the factor of safety (FOS) or stability factor (FS), and Pillar width/height (w/h) ratio. The factor of safety has been determined according to their estimated strength of coal Pillar and the assumed overburden load acting upon them. The acceptable width/height (w/h) ratio is generally taken less than or equal to 2.0, depending on the rock mass's physicomechanical conditions of the mine. A higher ratio than 2.0 has often caused coal pillar failure. The significance of this project is to maximize both reserve recovery and mining efficiencies without any discernible increase in geotechnical risk, particularly in the thick seam and higher cover depth mining situations. At a time when mining economics are at best marginal, the ability to remove unnecessary design conservatism without negatively impacting those catastrophic risks that relate to global mine stability should be of interest to all mine operators and is an important topic for discussion amongst the geotechnical society.