One of the main cost items in tunneling projects using tunnel boring machines (TBMs) in rock and soil is the cost of changing of damaged or worn cutting tools. Cutter change is a time consuming activity which can have a major impact on the daily advance rate (AR) and therefore, on the time and cost of constructing the tunnel. Accurate estimation of TBM performance and related completion time and cost requires reliable assessment of disc cutter wear by using appropriate methods. This study introduces a new empirical model for predicting cutter wear in moderate to very strong pyroclastic and mafic igneous rocks based on data collected from a long tunnel constructed by mechanized method in Iran. This includes monitoring and analysis of field data including cutter wear, geological parameters, and operational data from Karaj water conveyance tunnel project. The field data compiled in a database was subjected to statistical analysis for development of relationships between disc cutter life and geological parameters. Results of the analyses indicated reasonable correlations between intact rock parameters and tool wear. Some empirical equations are offered for predicting disc cutter wear in similar geological conditions. These equations were developed based on data from very blocky to blocky pyroclastic rocks and blocky to massive mafic igneous rocks with a UCS range of 30 to more than 150 MPa. (C) 2014 Elsevier Ltd. All rights reserved.