Suitable layout of gate roads related to slice mining in an ultra-thick unstable coal seam

We determined a suitable gate road layout in slice mining in an ultra-thick unstable coal seam, using theoretical analysis and numerical calculations. Based on plasticity theory in terms of limiting equilibrium, the width of chain pillar in the upper slice was calculated to be 18 m. The stress distribution in the chain pillar after the upper slice was mined out was described with numerical simulation. The extent of the effect of stress on the upper chain pillar on the lower solid coal was obtained on the basis of an elastic solution of a distributed force loaded on a half-plane. Three layout designs for lower gate roads were proposed and a stability factor was introduced to analyze the stability of the lower pillar with numerical calculation. Gate road translation was determined as the most suitable layout method, which maximizes the extraction rate on the basis of the pillar stability.