Method for Determination of Mined-out Roof Expansion Coefficient of Self-formed Roadway Without Pillar

With the background of gangue rib formed by fine sandstone roof of 6302 working face in Baoshan Coal Mine, the field measurement method of bulking coefficient and its influence on roof deformation of roadway are studied. By analyzing the mechanism of bulking coefficient and combining with engineering practice, the model of measuring bulking coefficient by natural calibration alignment method is established and the method of measuring broken expand coefficient in field is confirmed. And the field measurement shows that there are three stages of roof from collapse to compaction in goaf: the bulking coefficient decreases from 1.83-1.88 to 1.37-1.42 in rapid compaction stage; and in the initial stable stage, which slows down to 1.35 to 1.39. Then in the stage of slow compaction, and the change value of coefficient of fragmentation and expansion is less than or equal to 0.01. Furthermore, there is a certain correlation between the deformation law of roadway surrounding rock and the variation law of gangue bulking coefficient in goaf, which also has three sections, and the final movement amount of roadway roof and floor is 296 mm and 135 mm respectively. According to the gangue bulking coefficient in goaf and the surrounding rock deformation law of roadway, temporary reinforcement support is needed in the roadway during the gob-side entry retaining, and the supporting distance shall be at least 120 m.