MINE PRESSURE MEASUREMENT IN COAL PILLAR AND ITS APPLICATION TO ROADWAY DRIVEN CLOSE TO GOAF

Roadway driving close to the goaf is one of the effective methods to reduce the non-mineable coal reserve confined in the pillar and to raise coal productivity.The method is widely applied in the coal mines with relative simple hydrogeological conditions,such as the coal mines in North Anhui Coal Field,Lu′an Coal Field and so on.Because the stress condition in roadways close to goaf is rather different from the normal ones,the goaf roadways have high strata pressure and it is difficult to maintain.In order to solve the problems,many scholars have made site investigations by observation,numerical and physical simulations,and the structural analysis of the roof strata.But few long-term observations about mine stress and roof-floor closing displacement in the coal pillar,in which the goaf roadways are planned to drive,are reported.To understand the stress and the displacement,a special appendix opening is driven from the roadway in work face 655,the Second Liuqiao Coal Mine;and the measurements were made for about 146 days.According to the observation,it is found that the pillar can be classified as 3 zones in stress conditions as follows:(1) the plastic zone,0-4 m from the edge of the pillar;(2) the zone of abutment pressure on integrated coal,4-10 m from the pillar;and(3) undisturbed zone,10 m and above.In plastic zonet,he strata pressure is reduced with time,and the reducing speed is attenuated with time to zero after 146 days when the coal was mined.The strata pressures in other zones remained high during the observation.Therefore,the suitable place for the goaf roadway is seen in the plastic zone;and the pillar between the roadway and the goaf should not be larger than 4 m and not be earlier than 146 days after the coal is mined.The achieved results are successfully used in the mines of northern part of Anhui Province.