Analysis of overbreak effect on rockbolt cost in Extraction level Panel 29 West at PT freeport Indonesia using Monte Carlo regression and simulation analysis

Abstract

Grasberg Block Cave (GBC) is an underground mine with a block caving method managed by PT Freeport Indonesia. Grasberg Block Cave (GBC) consists of six mine levels including the Extraction Level Panel 29 West. One risk that can occur in the implementation of tunnel construction is overbreak. Overbreak can increase the damage that causes changes in the size of the width or height of the design, thus causing changes in the amount of rockbolt used. This study aims to determine the effect of overbreaks on the amount of rockbolt used, as well as to predict the overbreak and cost of rockbolt incurred on Extraction Level Panel 29 West. Data processing methods used were simple linear regression analysis and Monte Carlo simulation. Based on regression analysis, it is known that there is a significant influence between overbreaks on the amount of rockbolt used. A strong correlation (correlation) between overbreak value and the amount of rockbolt is shown by the correlation coefficient (r) of 0.63 and the coefficient of determination (r2) of 0.40, which means the effect of overbreak on the amount of rockbolt is 40%. Monte Carlo simulation results and regression analysis show overbreak predictions of 11.54 meters, so the number of rockbolts used increases from 10 units of resin bars and 9 units of cable bolts to 11 units of resin bars and 10 units of cable bolts. This caused costs to increase by $88.12 or 11% from the initial design cost of $ 837.33 to $925.45.