A methodology for estimation of the specific rock energy index using corrected down-the-hole drill monitoring data.

A methodology developed to estimate with accuracy the instantaneous specific rock energy using corrected downthe-hole (DTH) drill monitoring data is presented. A specific rock energy profile can be generated for every hole, and thus a drilling site can be mapped for this index. A special data acquisition system was developed to measure and register the following operational variables: penetration rate, torque, hole depth, pull-down force, air pressure, revolutions per minute (rpm) and the hammer percussion frequency, the latter obtained by sound recording and signal processing. The measured data are fed into two simulation models that estimate the power absorbed by the rock through impact, and then the specific rock energy index. The first of these models simulates the thermodynamic cycle of the DTH hammer, rendering the piston kinetic energy at impact, impact velocity as well as impact frequency. The second model is used for stress wave propagation analysis to estimate the effective energy delivered to the rock. Correlations were found between the specific rock energy and penetration rate, and between the specific rock energy and impact frequency, as well as between the penetration rate and applied torque, and between the penetration rate and impact frequency. [ABSTRACT FROM AUTHOR]