Mechanical Model for Calculating Surface Movement Related to Open-Pit and Underground Caving Combined Mining

Abstract

Surface movement under the combined mining of open-pit and underground caving is the main problem affecting safe and efficient mining. Taking the combined mining of Dahongshan Iron Mine as an example, a mechanical model for calculating surface movement range was established to reveal the movement mechanism. The topography, the caving zone, the gravel filling of the caving zone and mining depth were considered, and the surface principal stress was calculated. Based on the mechanical model, the mechanical relationship between the subsidence angle and the surface 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 zero displacement 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 the maximum surface prone cracking range calculated by mechanical model was found as the real subsidence angle. The subsidence angle calculated by the mechanical model was 60°, consistent with the observed subsidence angle of 64° in the Dahongshan Iron Mine, which verifies the reliability of the model.