Microseismic Analysis to Identify Stress Redistribution and Minimize Rockburst in DMLZ Cave Abutment,PT Freeport Indonesia

摘要

Seismicity has been interrupting production of DMLZ(Deep Mill Level Zone)block-cave mine.B-value analysis shows that seismic mechanism is caused by mining excavation.Excavation such as undercutting and mucking,triggers stress redistribution in rock mass.The seismic location plot with certain magnitude for recent six months indicates seismic is concentrated in the southern or active abutment consisting of diorite lithology.Subsequently,the lateral seismic evolution per a certain period also shows seismic concentrated in the southern abutment in the beginning and moved finally to the western abutment but seismic energy is concentrated in the southern abutment.Vertical seismic evolution shows seismogenic zone peak rises proportionally to production activity rate.A graph between seismicity and mining production shows seismic background rate for non-production activity and this rate can increase to 6-10 times because of production activities.Seismic events can trigger damage in rock mass called rockburst.Rockburst potency in rock mass is assessed by three parameters:strain energy density(SED),σc/σ1,and burst prone index(BPI).SED shows diorite and limestone are high rockburst rocks but skarn has the lowest rockburst potency.Ratio of σc/σ1 shows high rockburst potency occurs in three DMLZ rock masses.BPI in the tunnel vault is higher than the sidewall with the value is inversely proportional to cave front distance.Next,the back analysis of major rockburst cases indicates rockburst occurred in the active abutment that had not been undercut for a month or no undercutting activities.In short,objectives of this paper are to identify the cause of mining seismicity,divide abutment based on seismic and lithology,analyze changes seismic as well as energy concentration per a period laterally and vertically,observe relationship between mining production and seismicity,and analyze rock mass causes as well as tendency to rockbursting.Three advancement things of this research compared to the previous ones:it shows abutment division based on lithology and seismic,the relationship between seismicity to mining production,and solutions to minimize rockburst.