Analysis of Ground Support Stability and Monitoring at Extensive Vug Zone at Big Gossan Underground Mine, PT Freeport Indonesia


Mr Sitorus Eric, Mr Fadlan MaulanaSinaga, Mr Yali Irab, Mr Meiharriko Lubis, Mr Daulat Napitupulu, Mr Arjuna Ginting, Mr Anindito Mahendra

Big Gossan mine is sublevel stoping with paste backfill method which have 20 levels, from 2470/L as the lowest until 3180/L as the highest. As the mine being developed at 2510/L at 2009 UG Geotechnical has found indication of vug zone, rock type is silicified-weak skarn altered, RQD 60-70%, and Q value ranging from 3 to 6. Level 2510 plan to be maintenance area which will be utilized until end of mine. The dimension of vug zone is 7 mL x 11 mW x 24 mH, recommendation given was to install steel sets and fill the first 5 m above of the steel sets with paste. At 2013 failure has occurred which is caused the steel set bent. Geotechnical Dept. conducted analysis using GPR (ground penetrating radar) to conform the actual height of the paste above the steel set, after that it was decided to fill the vugzone full with paste, however this action will increase the load applied on the steel sets. Intensive monitoring is being undertaken since then. The objective of the monitoring is to observe if there is any deformations at the steel sets by using prism and surface laser scanner. The data obtained from 2013 until 2017 show no significant deformation of the steel sets therefore the area is safe to be utilized.