Development of a drill energy utilization index for aiding selection of drill machines in surface mines

Drill machines used in surface mines, particularly in coal, is characterized by a very poor utilization (around 40%) and low availability (around 60%). The main purpose of this study is to develop a drill selection methodology and simultaneously a performance evaluation technique based on drill cuttings produced and drilling rate achieved. In all 28 blast drilled through were investigated. The drilling was accomplished by 5 different drill machines of Ingersoll-Rand and Revathi working in coal mines of Sonepur Bazari (SECL) and Block-II (BCCL). The drills are Rotary and Rotary Percussive type using tri-cone rock roller bits. Drill cuttings were collected and sieve analysis was done in the laboratory. Using Rosin Ramler Diagram, coarseness index (CI), mean chip size (d), specific-surface area (SSA) and characteristic particle size distribution curves for all the holes drilled were plotted. The predictor equation for drill penetration rate established through multiple regressions was found to have a very good correlation with an index of determination of 0.85. A comparative analysis of particle size distribution curves was used to evaluate the drill efficiency. The suggested approach utilises the area under the curve, after the point of trend reversal and brittleness ratio of the respective bench to arrive at drill energy utilization index (DEUI), for mapping of drill machine to bench. The developed DEUI can aid in selecting or mapping a right machine to right bench for achieving higher penetration rate and utilizations.