Block size determination around underground openings using simulations

The in situ block size of the rock mass may be the single most important parameter influencing the stability and strength of some underground openings. Rock masses can often reasonably be characterized by a simple size-strength classification. The actual block size distribution is the product of the interaction between the joint orientation, spacing and persistence of that rock mass. Despite the importance of in situ block size, it is currently difficult to quantify. Block size is typically estimated as one of three indices, Rock Quality Designation (RQD), Volumetric Joint Count (Jv), and Block Size Index (Ib). These, being index properties do not quantify actual block size. The Centre de Technologie Noranda has initiated standardized scanline mapping techniques for the purposes of characterizing the discontinuities. This data is being used to quantify block size. Algorithms have been developed which simulate the division of a specified volume of rock by a number of joints or joint sets. These joints can be generated stochastically, based on summary statistics and inferred distributions of the field data, or deterministically, using the actual joints measured along the scanline.