Drillability predictions in Aravalli and Himalayan rocks – a petro-physico-mechanical approach

Dolomite, siliceous dolomite, phyllite, schist, leucogranite, pegmatite and gneissic rocks from the Indian Aravalli Hills and Bhutan Himalayan mountains were studied to examine the influence of petrographic and physico-mechanical properties on rock drillability. From petrographic assessments, a measure of grain size distribution, i.e. ‘granularity index’ and a ‘modi­fied saturation index’ are proposed. Extensive rock mechanics and drilling experiments were also perfor­med to correlate physico-mechanical properties with intact rock drillability. Statistical analysis revealed that no single petrographic parameter could completely explain the variance in drill penetration rate (DPR). The proposed indices and the petro-physico-mechanical approach helped in the rapid assessment of DPR in hard rocks.