Rock mass classification systems are widely used by geologists and geotechnical engineers for the classification, empirical design, and numerical modelling, especially during the first stages of a mining project, such as for Scoping and Pre-Feasibility studies.
The most used systems in the mining industry are represented by Laubscher RMR, Bieniawski RMR, Barton Q, Laubscher & Jakubec IRMR and Hoek-Brown GSI, consisting of empirical methods that characterise, in a simple and fast way, the rock mass quality while offering engineering applications to the geotechnical design, such as ground support design, pillar strength estimation, fragmentation, rock mass strength, caveability, among others.
The authors have been involved in all the engineering stages of numerous large mining projects, from the scoping to the construction, passing through due diligence and peer review. When reviewing the geotechnical data base of these projects, common and frequent errors seem to repeat, related to the collection of the basic geotechnical parameters.
The most frequent errors are associated to a mistaken distinction among natural and mechanical discontinuities, erroneous joint counts and consequently FF/m calculation and a wrong assessment of the RQD. Other typical errors have been detected in the assessment of the joint condition, most of them referred to the characterisation of the Joint Alteration (Ja) Barton parameter.
The aim of this paper is to show the impact of the geotechnical errors and mistakes over the geomechanical design, quantifying the variation in terms of rock mass strength, caveability, pillar strength, factor of safety, etc., that will produce a negative impact on both the capex, opex and high risk for a mining project and/or operation.
