MICROSEISMIC ANALYSIS TO IDENTIFY STRESS REDISTRIBUTION IN CAVE ABUTMENT AND MINIMIZE ROCKBURST IN DEEP MILL LEVEL ZONE, PT FREEPORT INDONESIA

• Main Author: Perangin-angin, Paulus
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/43966
• Institution: Institut Teknologi Bandung

Seismicity has been interrupting production of DMLZ (Deep Mill Level Zone) block-cave mine. Its b-value is 1.27 indicating the seismicity is caused by excavation. The combination result of seismic and geology data shows this seismicity concentrates in Diorite. Lateral seismic evolution shows seismic concentration changes from southern or active abutment to western one (both abutments comprise Diorite). However, seismic energy generally concentrates in southern abutment. Next, vertical seismic evolution shows seismogenic zone rise is proportional to mining production rate. A graph between undercutting, mucking, and seismic indicates a normal seismic rate (background) occurs when production activities stop but this rate increases 6-10 times when the production (undercutting and mucking) operates. The rise of seismicity increases rockburst potency in rock mass. It can be predicted by strain energy density (SED), ????????/???????? ratio, and burst prone index (BPI). SED shows Diorite and Limestone have high rockburst potency but Skarn rockburst potency is the lowest. In this study, cave material numerical modelling can also be done to calculate ????????/???????? and BPI. ????????/???????? shows rockburst potency in the abutment which is proportional to cave front distance. On the other hand, BPI can show rockbust tendency on vault and sidewall of extraction level tunnels at certain distances from the cave front. BPI is generally proportional to deviatoric stress but inversely proportional to panel distances from the cave front. Based on seismic, numerical and damage observation analyses, rockburst is summarized to occur in the active abutment that is not undercut for a month or more. Therefore, undercutting should be done continually in the area. In short, this research successfully find a relationship between main causes and seismic concentration changes laterally or vertically (related to mining production), causes along with rockburst potency of rock mass, and recommendation to minimize hazard in DMLZ.