Experimental study of caving and distribution of gangues influenced by roof fracturing in pillarless mining with gob-side entry retaining

GAO Yubing; HE Manchao; YANG Jun; MA Xingen

Abstract：Directional roof fracturing is one of the key techniques of gob-side entry retaining formed by roof fracturing and pressure release.To study the influence of roof fracturing on caving and distribution of the gangues,field tests were conducted in the S1201 mining panel of Ningtiaota coal mine.Based on the caving characteristics of the gangues,the caving step length of the main roof,the caving speed of the gob roof,the maximal diagonal size of the gangue body,the filling ratio of the gangue rib and the bulking stability of the gangues ware chosen as key characteristic parameters to explore caving and distribution laws of the gangues under different fracturing conditions.It was found that the variations of roof fracturing played a significant role in caving and distribution of the gangues in the gob area.Enhancing fracturing effects could help increase caving step length of the main roof,improve filling ratio of the gangue rib and reduce unstable range of the retained entry.The gangue size decreased and the caving speed accelerated with enhancement of roof fracturing.The fracturing height had a positive relation with the periodic weighting step and filling ratio of the gangue rib.The results indicate that as the charging amount increased from 1.2 kg to 1.6 kg,the average roof weighting step increased by appropriately 3 m,the filling ratio of the gangue rib increased by 5 ％ and the distance of the gangues to be stabilized decreased by 20 m.As the charging amount continued to increase to 2.8 kg,the average roof weighting step increased by 30％,the filling ratio of the gangue rib increased by 4％ and the distance of the gangues to be stabilized decreased by 9 m.In addition,the roof fracturing height also had remarkable effects on gangue caving.As the fracturing height increased from 7.5 m to 9.0 m (design height),the average roof weighting step increased by 2.3 m,the filling ratio of the gangue rib increased by 3.35％ and the distance of the gangues to be stabilized decreased by appropriately 23％.However,as the fracturing height continued to increase,there were no more obvious changes on the characteristic parameters.