Research on safety roof thickness and surface risk zoningmethod in mined-out area of open pit coal mine

In order to realize the three-dimensional dynamic control of the risk of mined-out area in open-pit coal mine, and to ensure the safety of open pit mining equipment and personnel during the period of passing through the mined-out area, the hidden geological disaster exploration and control engineering practice in the gob of large open-pit coal mine in Pingzhuang mine area of Pingshuo mining area, the combination of numerical analysis, physical simulation and on-site measurement was used to study the development law of cracks in the overlying rock mass and the deformation and failure of surrounding rock and the influence of equipment on the ground. Through the research, a method for determining the safe roof thickness of the longwall working face mined-out area was established, based on the height of the overburden "two belts" and the influence depth of the equipment on the ground, and a surface hazard zoning method of mined-out area was also proposed,based on the gob plane projection boundary, the separation range boundary, the inner boundary of "masonry beam" structure area and the movement basin fracture boundary. Combined with the characteristics of various open-pit mining equipment and the difference of the requirements for safe operation environment, the corresponding hazard zones were determined.