Study on stability of district sublevel coal pillar with longwall face re-mining in shallow depth coal seam

In order to determine the type and stability of the district sublevel pillars in shallow coal seam when converting room-and-pillar mining into longwall mining,t he theoretical calculation method was adopted to analyze the type mechanical characteristics and stability of the segment pillars during repeated mining in the room-and-pi Ilar mining area and the mechanical model of the pillar was established,and effective bearing width calculation formulas of four different types of segment pillar were prese nted: two-pillar-and-one-roadway without backilling,threepillar-and-two-roadway without backilling,two-pillar-and-one-roadway with backilling,and three-pillar-and tworoa dway with bakilling. Taking Gongjiata Coal Mine in Erdos area as the research object,the instability coefficient of the four kinds of segment pillars were obtained. The resu Its indicated that the instability coefficient of two-pillar-and-one-roadway segment pillars with and without backilling and three-illar-and-two-roadway segment pillars witho ut backlilling was greater than or near 1 ,which meant instability risk. The results also showed that the instability coefficient of the three-pillar-and-two-roadway segment pill ars wasO.64 ~ 0. 87. It could ensure pillars were stable during longwall mining,which could meet the requirements of mining safety and maximize the coal production.