Improving the GSI Hoek-Brown criterion relationships

The aim of this paper is to expand the database linking the GSI and the Hoek-Brown criterion parameters mb, s and a. The database includes in situ stress failures of rock masses and of laboratory testing where rock mass quality has been interpreted. Assessment of the database showed that whilst the current relationships provide reasonable fits to the data, improved fits could be found by using equations developed by the authors. The new equations are similar to the existing ones. The substantial change is the one that is proposed between GSI and a, which allows the parameter a to vary between 0.5 for GSI =100 and 1.0 for GSI≤10.