Development of Seismic Activity Zones in Undermined Rock Mass in Hybrid Opencast/Underground Mining in Kirovsk Mine

The seismic activity in undermined rock mass in a mine at the Khibiny Massif is analyzed over the period from 2008 to 2020. The influences on deformation, tensile fracturing and caving in undermined rock mass are revealed. Three zones of deformation of different nature and velocity are identified in undermined rock mass in Kirovsk Mine: the zone at the juncture of underground and opencast mining; the zone of overhanging rocks; the zone of two- and three-side buttress at the edges of operating deposits. It is found that mining with head-on fronts, with formation of a support pillar and with overhanging of an uncaved rock mass beam is adverse. The pillar collapses later on and deformation of the pillar-supported rock mass during breaking of the butt section on sublevels occurs in the dynamic mode with high seismic activity both in terms of the number of seismic events and their energy emission. It is found that the width of the seismic activity band and the caving pitch of the overhang depend on the height of undermined rock mass.