A methodology for rock mass characterisation and classification to improve blast results

The rock mass description has been for a long time considered as a first step prior to all civil and mining projects involving rock mechanics problems. In this paper, a methodology is proposed which aims at the characterisation of the two rock mass components: discontinuity network and rock matrix. It was developed within the frame of the EU research project LESS FINES (Proceedings of the Second World Congress on Explosives and Blasting Technique, 10-12 September 2003, Prague, Czech Republic, pp. 335-343). Three quarry sites were chosen for the analysis: El Alto (Spain), Eibenstein (Austria) and Klinthagen (Sweden). The discontinuity network was described using the 3D stochastic simulations of discontinuity networks using the SIMBLOC program methodology. Several parameters assessing the density (specific surface), the interconnectivity (interconnectivity index) and the anisotropy (anisotropy index and anisotropy vector) of the discontinuity network as well as the 3D fractal dimension of the rock mass were introduced and evaluated for the three sites. The rock matrix microstructure was characterised by the means of the experimental determination of several mechanical and physical parameters. Laboratory measurements performed on cores coming from the blasted blocks allowed a fine characterisation of this microstructure status. The analysis of the results led to a precise characterisation of the differences between the sites and between the zones/benches of a same site and to the classification of these zones according to the discontinuity network intensity and the rock matrix continuity. Moreover, some implications could be pointed out with regards to the explosive energy types recommended for each rock mass class.