Geomechanical behavior of crown pillar between ground surface and mined-out void roof in mining blind ore body on Sheregeshevsky deposit

Abstract

Sheregesh Mine extracts ore reserves at the Levels of +255 ÷ +115 m in four sites at the depths of 470–700 m and deeper and produces annually more than 4.5 Mt of ore. The upper ore edge in Podruslovy site is spaced at 290–320 m from ground surface. The major ore reserves occur within the depth interval from 300 to 700 m below ground surface. Enclosing rock mass is composed of limestone, porphyry, skarn and other rocks which belong to stability class II. Considering the physical and mechanical properties of ore and enclosing rocks, the effective stresses and the geodynamic phenomena observable beneath the Level of +255 m, Sheregesh Mine operates in the rockburst-hazardous conditions. The geomechanical behavior of a crown pillar between ground surface and mined-out void roof in mining the ore body in Podruslovy site under conditions of rockburst hazard is assessed. The influence of the room-and-pillar and subsoil caving variants on the roof of the mined-out void is shown. The mathematical modeling delineates the concentration zones of stresses and inelastic strains in adjacent enclosing rock mass. The sizes of the crown pillar are estimated experimentally using geophysical methods. The pillar thickness ranged 420 to 300 m, then, three boreholes drilled from ground surface showed the thickness variation in the range from 309 to 12.7 m. Using the gravimeter survey in combination with orthophotomap, the outlines of the underground void and the ground surface subsidence are determined. The configuration layouts of holes for dry rock backfill by-pass for filling the void in Podruslovy site are presented.