Research On Movement Features Of Covering Layer During Open Pit To Underground In Xingshan Iron Mine Of Shougang

In the process of open pit to underground, in order to attain a better effect of stagnant water and to prevent rock burst, a rational structure covering layer is necessarily paved on the bottom of open pit before mining in mines which utilize sublevel caving method without sill pillar. The covering layer will change underground mining activities happen, simultaneously, it will affect the layer thickness and structure. So it has a great significance to investigate movement features of covering layer for identifying a rational structure and thickness of covering layer.Take Xingshan iron mine from open pit to underground Shougang an example, a similar experimental conditions is established accoring to the similarity law, a similar physical model of covering layer from open pit to underground was designed and constructed. According to the different combinations of granulometric composition, thickness, humidity and ore drawing condition, mobile physical simulation experiments of covering layer were finished, at the same time, the establishment and use of numerical simulation software PFC2D model reproduced the moving process of loose layer. Through the comparative analysis of results of physical simulation and numerical simulation, the movement rule of covering layer in the process of underground mining was obtained.From the study of model, the covering layer was changed with the underground mining activity. The movement rule of covering layer was affected by the ellipsoid of ore drawing, its affect limitation range was depended on the height of loose ellipsoid, the general height of covering layer is close to 1.5 times of drawing ellipsoid's. In the process of the downward covering layer, the movement speed along the axis of loose ellipsoid is fastest. The downward speed of fine-grained covering rock is faster than the one of coarse-grained covering rock. If the rock lumpiness between the border of ore and rock is too thin, it will cause over early ore dilution, it is suggested that the rock lumpiness of the border should be as near as the average limpiness of underground mining. According to the experimental study of thickness of different covering layers, when the thickness is small, the surface of covering layer is rugged to be waved and disadvantaged of the function realization of stagnant water, wind-prevention and rock burst, so it is suggested that the covering layer thickness of Xingshan iron mine should be better more than 40m.