关键词: 露天转地下　, 境界顶柱　, 顶柱厚度　, 隔一采一　, 胶结充填　, 废石散体充填

Abstract: After the transition from open-pit to underground mining,unreasonable crown pillar thickness under the influ ence of mining disturbance can easily induce goaf collapse and slope instability,seriously affecting the safe production of the mine.Taking a mine in Southwest China that has transitioned from open-pit to underground mining as the background,a sys tematic study on the mechanical stability and reasonable thickness of the boundary crown pillar was carried out using a com bined method of theoretical calculation and numerical simulation.In theoretical analysis,a simply supported beam mechanical model and the cusp catastrophe theory were employed to derive the calculation expression for pillar thickness and clarify its reasonable range.In numerical simulation,a three-dimensional numerical model was established using FLAC3D software to sim ulate the mechanical response characteristics of the ore extraction-backfilling process under seven working conditions,where the pillar thickness was gradually reduced from an initial 40 m to 10 m in steps of 5 m.Key mechanical indicators such as plastic zone propagation,stress distribution,and vertical displacement were analyzed.The results show that when the pillar thickness is 10 m,the plastic zone penetrates to the surface,leading to overall instability of the goaf.At a thickness of 15 m,the plastic zone does not connect with the upper boundary of the pillar,and the pillar structure remains stable.The tensile stress at the upper boundary of the pillar exhibits a trend of "first decreasing,then increasing,and then decreasing again" with increasing pillar thickness,with the minimum tensile stress occurring at 15 m.The vertical displacement decreases with increasing pillar thick ness and tends to stabilize when the thickness exceeds 15 m.Based on the study results and field conditions,the optimal boundary pillar thickness is determined to be 15 m.The findings can provide a reference for determining reasonable reserved pillar thickness in similar mines.

Key words: open-pit to underground,crown pillar within boundaries,crown pillar thickness,skip-one-mine-one,cemented filling,non-cemented filling