Rockburst prevention in deep ore pillars by forming relieve slots (for the Lovozero raremetal deposit)

Abstract

Lovozero GOK which develops the Lovozero rare metals deposit is the only supplier of raw materials for the rare metal industry in Russia. The depth of mining at the deposit having reached 600 m is gradually increasing and should reach 900 m. The Federal Service for Environmental, Technological and Nuclear Supervision RF refers the deposit to rockburst-prone and dangerous starting from a 400 m depth. With increasing depth, there is a danger of rockbursts in pillars supporting the overburden, for which it is necessary to provide for appropriate preventive measures. The study has examined the problem of stress distribution in shock-hazardous near-track pillars with discharge slots for the conditions of the Lovozero deposit which is tectonically highly stressed. A variant of the prevention of shock hazard in pillars is provided through the formation of discharge gaps in the sides of the mine, with the help of which the stress concentration is transferred from the excavation boundaries to the pillar's core. The relieve slot formation weakens the bearing capacity of the pillars. However, the formation of unloading slots creates conditions for the middle part of the pillars under volumetric compression, as a result of which the pillars carrying capacity increases. The analysis of the increase in strength of the pillars when working under the conditions of volumetric compression is produced using the shape factor (determined by the formula E. Zern). The data obtained indicate that in low wide pillars, which are contoured at depths above 500–550 m, the weakening effect of the gaps is leveled by the shape of the pillars. Developing preventive measures for shock hazard, the specific bearing capacity of the pillars with / without discharge gaps has been calculated at their location at depths up to 900 m from the surface for the conditions of the Karnasurt mine, which is planned to be mined in the coming years

Keywords

• pillars
• rockbursts
• slots
• bearing capacity
• Zern coefficient
• deepening