ORIGINAL PAPER Applications of NTNU/SINTEF Drillability Indices in Hard Rock Tunneling S. Zare • A. Bruland Received: 11 December 2011 / Accepted: 10 April 2012 / Published online: 4 May 2012 Ó Springer-Verlag 2012 Abstract Drillability indices, i.e., the Drilling Rate Index TM (DRI), Bit Wear Index TM (BWI), Cutter Life Index TM (CLI), and Vickers Hardness Number Rock (VHNR), are indirect measures of rock drillability. These indices are recognized as providing practical character- ization of rock properties used in the Norwegian University of Science and Technology (NTNU) time and cost pre- diction models available for hard rock tunneling and sur- face excavation. The tests form the foundation of various hard rock equipment capacity and performance prediction methods. In this paper, application of the tests for tunnel boring machine (TBM) and drill and blast (D&B) tunneling is investigated and the impact of the indices on excavation time and costs is presented. Keywords Drillability indices  DRI  BWI  CLI  VHNR  Hard rock tunneling 1 Introduction The Drilling Rate Index TM (DRI), Bit Wear Index TM (BWI), and Cutter Life Index TM (CLI) are registered trademarks of the Foundation for Scientific and Industrial Research (SINTEF) and NTNU in Trondheim, Norway. In the following text, the trademark symbol is omitted to ease readability. The drillability tests were developed at the Norwegian University of Science and Technology (NTNU) in the early 1960s. Recent developments have focused on specifica- tions and creation of new tests and procedures (NTNU 1998a, b, c; Blindheim and Bruland 1998; Dahl et al. 2007). The DRI, BWI, and CLI are indirect measures of rock drillability. Because of the weakness of BWI for prediction of drill bit life in drill and blast tunneling, the wear parameter Vickers Hardness Number Rock (VHNR) is used instead of BWI in the updated prediction models (NTNU 1998a, 2007b, 2009). The DRI and BWI were developed at the Department of Geology and Mineral Resources Engineering at NTNU in the years 1958–1961 (Selmer-Olsen and Lien 1960). The method was tested in the field during the next 10 years, resulting in minor adjustments. The CLI was developed at the Department of Civil and Transport Engineering at NTNU in the years 1980–1983. Systematic follow-up of drilling and boring in rock quarries and tunnels has been carried out since 1972. The data have been normalized and related to the drillability indices of representative rock samples. These indices are recognized as providing practical characterization of rocks applicable in time and cost pre- diction models available for hard rock tunneling and sur- face excavation (NTNU 1998a, b, c, d, e, f, g, h, i, j, 2007a, b, c, 2009; Zare 2007). Apart from the NTNU laboratory (in cooperation with SINTEF), where several thousand tests have been done for many projects around the world, several other laboratories have also set up equipment to perform the same tests. Even though there are some publications that show the tests and procedures, there is not a sufficient number of publications focusing on application of the indices and S. Zare (&) Department of Mining, Petroleum and Geophysics Engineering, Shahrood University of Technology, Shahrood, Iran e-mail: zare@shahroodut.ac.ir A. Bruland Department of Civil and Transport Engineering, Norwegian University of Science and Technology, Trondheim, Norway 123 Rock Mech Rock Eng (2013) 46:179–187 DOI 10.1007/s00603-012-0253-y