Study on width optimization of narrow pillars in strip Wongawilli mining

Strip Wongawilli mining is a kind of efficient and environmental mining method, which has great significance in high quality marginal coal recovery, surface subsidence control and work face safety.It is initially search in strip Wongawilli mining these days in our country compared to mature application in US and Australia.In order to study the characteristics of narrow pillars, in hedong L21001 coal mine, the coal pillar’s stress characteristics are analyzed, the calculation method of coal pillar size is obtained, two different mining plans are proposed, FLAC^3D software is used to analyze the plastic zone, displacement and stress characteristics of surrounding rock near roadway, safety precautions in adopted in working face.The results show that the total width of narrow pillars are 60 m in the initial mining phase.The 1.5 m-wide narrow pillars play a temporary supporting role.With the work face moves on, the narrow pillars will collapse at monment or lose their supporting ability in a short time.When 1 m and 3.5 m narrow pillars are used simultaneously, the smaller naorrow pillars will collapse but the larger narrow pillars have a strong bearing capacity, which can ensure the safety of continuous mining machine.When the roof is caved in, the stress of the original rock is transferred to the narrow pillars, and stress concentration is formed around the narrow pillar.The stress concentration coefficient is 2-3.The narrow pillars effectively bear the load of the overlying strata, making the roadway and the overlying strata in the stress reduction zone.The field measurement shows that the surface displacement of the roadway in the middle of the branch lane is larger than that at both ends of the branch lane, the subsidence of roof in the second plan is smaller, so is the plastic zone.The optimized plan has higher reliability and maximizes economic benefits on the premise of ensuring safe and efficient production.