1. Bieniawski, Z.T., Estimating the Strength of Rock Materials, J. S. Afr. Min. Metall., 1974, vol. 74, pp. 312–320.
2. Mathews, K.N., Hoek, E., Wyllie, D.C., and Stewart, S.B.V., Prediction of Stable Excavation Spans for Mining at Depths Below 1000 Meters in Hart Rock, Golder Associates Report to Canada Centre for Mining and Energy Technology (CAANMET), Department of Energy and Resources, Ottawa, Canada, 1980.
3. Bulychev, N.S., Mekhanika podzemnykh sooruzheniy (Mechanics of Underground Structures), Moscow: Nedra, 1989.
4. Laubscher, D.N., A Geomechanics Classification System for the Rating of Rock Mass in Mini Design, J. S. Afr. Min. Metall., 1990, vol. 90, no. 10, pp. 257–273.
5. Hoek, E., Wood, D., and Shah, S., Modified Hoek-Brown Criterion for Jointed Rock Masses, Proc. ISRM Symp.: Eurock 92 Rock Characterization, J. A. Hudson (ed), British Geotechnical Sociiety, London, 1992.