The Law Of Stratum Movement Induced By Underground Mining In Fenghui Coal Mine And Long-term Stability Evaluation Of The Goaf Site

The strata movement and surface subsidence caused by underground mining makes a large area of land collapse.After mining,there will be a long-term residual settlement process in the goaf.When building above the goaf,if the surface residual movement deformation and residual differential deformation of the goaf are too large,the safety of the new construction will be threatened.Based on the Fenghui coal mine,this paper establishes a three-dimensional geological model,and uses FLAC^3D to study the law of strata movement and surface subsidence induced by mining in multiple underground working panels of Fenghui coal mine.At the same time,the residual deformation process of goaf in Fenghui coal mine is simulated by equivalent parameter transformation method,and the long-term stability of the goaf site is evaluated.The main results are as follows:(1)After the panel is excavated,the roof caving directly and contacts with the floor,leaving only a part of cavity area near the open-off cut and stop-working line.Due to the influence of topography,the surface subsidence basin of each panel is inclined to the side with higher topography.The mutual influence of overburden movement after mining at adjacent working panels is mainly manifested in that mining at subsequent working faces will lead to the destruction of the stable overburden structure and further subsidence of the subsided surface.After all panels are mined,the surface subsidence basin is elliptical with the long axis in the east-west direction,and two sub-basins appear in it.(2)During the calculation of residual deformation of goaf,the surface residual settlement gradually increases and then tends to be stable with the strengthening of the parameters of broken rock mass.After the residual deformation calculation completed,the residual displacement of overlying strata near the open-off cut and stop-working line is larger than that in the middle of goaf.What's more,as the panels are mostly gathered in the the west side of the middle of goaf group,and the sizes of the panels in this area are large,so the biggest residual settlement of the site appears on it.However,the places with large residual horizontal deformation,large residual inclined deformation and large residual curvature of the surface are distributed on both sides of the mining boundary of the goaf group,and are roughly parallel to the mining boundary.(3)The long-term stability of the site is evaluated by four indexes:residual settlement,residual horizontal deformation,residual inclined deformation and residual curvature,and the site is divided into unstable zone and basic stable zone.In the unstable zone,the residual differential settlement reached 400mm,the maximum residual differential horizontal deformation reached 3.5mm/m,and the maximum residual differential tilt deformation reached2.5mm/m.If construction activities are carried out in this area without treatment,the uneven residual differential deformation will seriously threaten the safety of the structure.