Evolution characteristics of mining fissures in overlying strata of stope after converting from open-pit to underground

Abstract

The mechanical properties and engineering response characteristics of rock under the interaction of slope rock mass and underground mining have always been a major difficulty in research. In this paper, the deep ore body of No. 2 pit of Jinning Phosphate Mine was taken as the engineering background. In order to reveal the deformation and failure process and evolution laws of fractured rock masses, semi-quantitative indicators such as the shape, quantity, density, size, distribution range, spatial position, and rock mass movement angle of the developed fissures were analyzed. In addition, the morphological equation of the outermost fracture zone of the slope, the surrounding rock of the underground stope, and the overlying rock mass was established after the open-pit was converted to the underground. Combined with the physical model experiments (model slope height was 200 m; slope angle was 55°), MatDEM numerical simulation showed that (1) after the pillar mining was completed, the fissures at the left and right ends of the overlying rock mass were mostly long fissures with medium and high angles (30° ~ 90°), while the middle part and near the main fissures were mostly small fissures with low angles (0° ~ 30°). ( 2) The fracture evolution of the overlying rock mass in the mining area was a dynamic stratification process that extends upward in turn, accompanied by shedding, falling, and collapse. This study can provide theoretical guidance for the safe and effective mining of gently inclined phosphate rock.

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