Long-term stability evaluation and coal pillar design methods for strip mining

The coal pillar will peel and scale down under the effects of underground water,weathering,etc. ,leading a progressive pillar failure. Based on the progressive peeling behaviors of coal pillar and properties of peeled coal depos- it,this paper established a non-evenly peeling pillar model;the factors affecting pillar peeling and the relationship be- tween pillar peeling and safety factor had been analyzed;a long-term stability evaluation method for strip pillars had been proposed;finally,the synergic relationships among recovery ratio,subsidence control and safety factor has been discussed. Analysis results shows that the pillar peeling is affected by bulk factor of coal,angle of repose and width- height ratio of mining tunnel,and the degree of pillar peeling can be determined by peeling angle. The increase of pil- lar width-height ratio can reduce the effects of peeling angle on pillar stability. This model can be utilized in long-term failure risk evaluation for strip pillars.