Similar model study on the principle of balanced mining and overlying strata movement law in shallow and thin coal seam based on N00 mining method

Abstract

To study the principle of balanced mining and the overlying strata movement law in the shallow and thin coal seam using the N00 mining method, based on theoretical analysis, similarity experiments, and on-site measurements in Xintai coal mine, the characteristics of balanced mining and roof movement law between the N00 mining method and traditional mining method were compared and analyzed. The balanced mining characteristics of the N00 mining method were analyzed from four aspects: the movement characteristics of the strata, the damage coefficient of the strata, the subsidence displacement of the strata, and the development of the strata's cracks. The fracture characteristics analysis of the strata showed that the three zones of the overlying strata in traditional mining method are “collapsed zone (I)”, “fractured zone (II)”, and “curved zone (III)”, while the three zones of the overlying strata in the N00 mining method are “collapsed zone (I)”, “curved zone (II)”, and “protected zone (III)”. Through the analysis of the damage coefficient of the strata, it was found that the N00 mining method uses the bulking characteristics of the strata to increase the damage coefficient of zone I, decrease the damage coefficient of the other two zones, and reduce surface damage. Through the analysis of the roof subsidence displacement, it was found that the N00 mining method reduces the subsidence of zone I, II and III by using the bulking characteristics of the strata, and the model surface has basically no subsidence displacement, while the traditional mining method still has subsidence displacement at the top of the model. Through the analysis of the cracks development of the strata, it was found that compared with the traditional mining method, the N00 mining method has more developed cracks in zone I and more complex cracks, and the number of cracks in the other two zones is less than that of the traditional mining method. Finally, through on-site measurements, it was discovered that traditional mining method are prone to significant surface subsidence displacement, whereas the N00 mining method mitigates this phenomenon by means of cutting-strata, expanding the range of zone I, making the strata fully bulked, increasing the damage coefficient of zone I, increasing the number of cracks in zone I, reducing the damage coefficient of the strata near the surface, curtailing the subsidence displacement in surface-proximal strata, reducing the incidence of cracks in the strata close to the surface, safeguarding the surface strata, and ultimately achieving balanced mining.