Design of coal pillar with roadway driving along goaf in fully mechanized top-coal caving face

Small coal pillar with reasonable width plays important roles in not only improving recovery ratio and eliminating dynamic disasters, but also in keeping the stability of entry surrounding rock. In order to analyze reasonable layout of gob-side entry driving in fully mechanized top-coal caving face (FMTC face), numerical simulation, in-situ measurement and theoretical calculation are carried out. The stress redistribution rules of coal mass in dip direction are put forward by metering the stress after coal extraction. At the same time, mechanical characteristics of coal pillars with different widths, 3 m, 5 m, 7 m, 10 m, 15 m and 20 m, respectively, are obtained by analyzing stress field, displacement field and fractured field characteristics. Reasonable width of district sublevel coal pillar is determined by calculating the width of limit equilibrium region and the cracked range of the entry surrounding rock due to mining of adjacent face based on the results of in-situ measurement and numerical simulation. The engineering practice proves that the width of coal pillar is scientific and reliable. It provides a scientific basis for reasonable layout of gates and determining parameters of the coal pillar in FMTC face. It can be favorable to improve maintenance states of entry, and also benefit to improve the recovery in FMTC face, and it provides beneficial lessons for determining reasonable width of gob-side entry driving of other similar conditions.