Development of the Methods for Discharging a Rock Mass during Second Working at a Rockburst Hazardous Iron Ore Deposit
At the Sheregeshevskoye iron ore deposit, which is hazardous for rockbursts, development of the methods for unloading a rock mass during second working is studied. In the formation of the main volume of ore mining, four areas are involved, located at the depths of 400-600 m and more. Development of ore bodies is accompanied by the dynamic phenomena in the form of shocks, shots, and stabbing. According to the level of stresses acting in the rock mass, the sites are classified as hazardous for rockbursts. In the process of mining the Novy Sheregesh site by the system for the development of the sublevel caving from top to bottom, a rock ledge with a diameter of 100 m and a height of 250 m was formed. Assessment of the stress-strain state of the rock mass was carried out, which showed the location of zones of concentration of stresses and shocks in the western and eastern parts of the vicinity of the mined-out spaces. Zones of inelastic deformations are formed along the entire area of the worked-out spaces, and are removed deep into the massif by 5-10 m. To reduce the intensity of shocks and stress values, the layouts of horizontal unloading wells with their subsequent camouflage blasting were developed and tested. The wells allowed to relieve the rock ledge from high stresses and shocks for 2-3 years. With additional drilling of unloading wells with a total length of more than 2000 m in the rock ledge from drift № 4, horizon + 185 m and from port № 34a, the number of shocks decreased by 2-3 times with an explosive mass of 123-137 t/year.