Drillability assessments in hard rock

Drillability is an important parameter in order to assess the influence that intact rock properties have on performance prediction and cost evaluations in connection with drill-and-blast tunnelling, TBM tunnelling, excavations by roadheaders and hydraulic impact hammers and also rock quarrying. Especially in hard rock conditions, drillability will be of great importance for selection of excavation method and a successful project execution. Unanticipated situations and/or inappropriate assessments can result in considerable delays and great risk of cost overruns. Reliable predictions are therefore required; prediction of net penetration rate and tool wear, time consumption and excavation costs, including risk and assessing risk linked to variation in rock mass boreability, establishing and managing contract price regulation. Several methodologies are available to assess drillability (i.e. rock strength, rock surface hardness, rock brittleness, rock abrasivity or rock petrography). This paper includes a review of the state-of-the-art and discussion of relevant parameters that involves drillability assessments in hard rock conditions.