[en] Big quarries are mined out in the Tournai's region (Belgium) for cement or crushed raw materials production.
The development of this industrial activity is due to famous outcrops of carboniferous limestone in the region. The rock masses
in the area are characterised by three sets of discontinuities among which two have a near vertical dipping; and these sets are
intersected a time to time by some typical faults. It is generally recognised that, when subjected to the effect of percolating
water, the limestone undergoes a weathering leading to very poor material on the mechanical point of view. Such a material
cannot be used as crushed rock. When designing the rock blast, the mining engineer has to plan and drive the operations in
order to decide about the most suitable destination for the mined out material, i.e. crusher of waste dump.
A particular method has been developed in this paper to assess continuously the quality of the rock being drilled for blast
holes. This uses the drilling logs (i.e. weight on bit, rate of penetration, and rotation torque) to evaluate the strength of the rock
mass.A mechanical 'energy index' that can be related to the destruction specific energy is defined.A correlation is then built
with the GSI (Geological Strength Index) as described by Hoek and Brown (1997). The working method involves the definition
of the GSI per zone and a specific treatment to assess the magnitude of the corresponding energy index. This can be used to
update the geological map of a quarry based mainly on the directions of natural fractures.
