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Einstein, H.H., Thompson, D.E., Azzouz, A.S., O’Reilly, K.P., Schultz, M.S., and Ordun, S. (1983). Comparison of five empirical tunnel classification methods – accuracy, effect of subjectivity and available information. In: Proceedings of the 5th ISRM Congress, 10-15 April, Melbourne, Australia. ISRM-5CONGRESS-1983-107