Preliminary study on theoretical analysis of surface movement range in mining steeply inclined ore body in metal mine

To reveal the law of surface movement in mining steeply inclined ore body of metal mines and effectively predict the range of surface movement, taking the surface movement of the hanging wall of steeply inclined orebody mining in Gongchangling Iron Mine as an example, a mechanical model for calculating surface principal stress distribution and surface prone-cracking range was established. The topography, waste rock back filling and mining depth were considered in the mechanical model. Based on the mechanical model, the mechanical relation between the subsidence angle and the surface prone-cracking range was established, and the definition of subsidence angle was supplemented: the subsidence angle is the angle measured from the horizontal of the moving boundary line, a straight line with a displacement of 0 from the edge of the deepest extraction level to the surface and the largest surface cracking range. A trial calculation method for calculating the subsidence angle was proposed: by presetting different subsidence angles, the subsidence angle corresponding to maximum surface prone-cracking range calculated by mechanical model is the real subsidence angle. After the real subsidence angle is obtained, the surface prone-cracking range and depth can be determined by the mechanical model. At the same time, based on the limit equilibrium principle, the mechanical relation between the surface prone-cracking range and the slip of block was established, and the calculation method of the surface potential collapse range was proposed: the range can be determined by setting up limit equilibrium equations for potential sliding blocks corresponding to different cracking points in the surface prone-cracking range, and determining whether the blocks will undergo shear slip in turn. The subsidence angle at hanging wall caused by underground mining of the footwall iron-bearing belt of Gongchangling Iron Mine is 60°, the horizontal distance from the location with initial slip risk to the initial mining location is 130m, and the potential slip angle is 55°. According to the field experience of combined open-pit and underground mining in Gongchangling Iron Mine, timely and compact backfill of underground goaf and optimization of mining space-time sequence and mining intensity can effectively control surface movement, and realize safe combined mining of open-pit and underground in metal mine.