Document Type

Conference Paper

Publication Date


Publication Details

This conference paper was originally published as Hossaini, SMF, A comparison between Hoek-Brown and Bieniawski criteria for coal and rocks, in Aziz, N (ed), Coal 1998: Coal Operators' Conference, University of Wollongong & the Australasian Institute of Mining and Metallurgy, 1998, 213-223.


The applicability of Bieniawski and Hoek-Brown empirical strength criteria has been assessed for different groups of coal and various types of intact rocks by using a vast number of published triaxial test data from various places. Analysis of individual data sets revealed that the traditional forms of the criteria do not have a perfect agreement with the data. A strong negative correlation has been observed between B in Bieniawski's criterion and m in Hoek and Brown's criterion with uniaxial compressive strength of materials. Both criteria have been modified and empirical relationships have been introduced for coal as follows: m = 62.903 - 34.213 (log Pc) 0.9772 0.8889 B = 10.152- 4.709 (Log Pc ) Similar relationships have been developed for different rock types as well. A comparison between the applicability of each of the above approaches with the conventional criteria reveals a very significant advantage for new approaches and a supremacy for the Bieniawski criterion in all cases particularly in the case of coal. The modified Bieniawski criterion fits coal as well as different types of rocks with excellent accuracy. The modified Hoek-Brown criterion gives a good result for rocks but does not fit coal data quite well. In other words, Hoek-Brown criterion is not an suitable one for coal.