Study on surface deformation law of coal pillar-filling combined control

Aiming at the problems of coal resource recovery under buildings in mining area, difficulty in normal production and continuation of working face and large surface deformation, based on the roadway-by-roadway cemented filling method in Albas No.2 Coal Mine, FLAC^3D simulation software and mining subsidence prediction analysis software are used to compare and study the influence of the change of the filling rate of cemented slurry with coal gangue and fly ash as aggregate on the surface deformation law and the internal stress distribution characteristics of the filling body when different coal pillar widths (6 m, 12 m, 18 m and 24 m) are retained.The results show that the combined control of protective coal pillar and cemented backfill can effectively reduce the subsidence of overlying strata, but the surface subsidence centered on the coal pillar does not show a completely “asymmetric” distribution and tends to gradually show a “flat bottom” phenomenon with the increase of coal pillar width.The vertical stress peaked in the middle of the filling body (21.85 MPa), and the decreasing trend extended to both sides.The optimal scheme of combined control is that the protective coal pillar is 12 m and the filling rate is 85%.At this time, the deformation of the ground structure (ε≤1.4 mm/m, i≤2.4 mm/m) meets the Class I fortification standard of surface building (structure) protection.Compared with the 6 m protective coal pillar, the horizontal movement value of the surface is reduced from 4.72 mm to 2.78 mm, with a decrease of 41.10%.