Determining the size and shape of blocks from linear sampling for geotechnical rock mass classification and assessment

Classifying and assessing geotechnical aspects of rock masses involves combining parameters in various ways, guided by empirical considerations, to derive quantitative geotechnical parameters. Geological structures and the deformation history of rocks underpin the nature of rock masses. The kinematics of a deforming rock mass may occur as sliding along throughgoing discontinuities or as distributed sliding on block faces. Distributed sliding will tend to disrupt the continuity of planar structures such that data on the size and shape of blocks is needed, rather than relying on discontinuity orientation data alone. Orientation and spacing data can be combined to provide a geometric analysis of block systems from linear samples, such as drill core. Dihedral angles and spacing of sequential pairs of discontinuities provides a sample of the size and shape of blocks that can be interpreted stereologically. Further detail can be derived by combining neighbouring intersections that enclose or partially enclose individual blocks. The shape and size of a block can be represented on a stereograph with the enclosing faces shown as poles and their perpendicular distance from an arbitrary point inside the block shown as a number. Identifying the size and shape of specific blocks rather than relying on statistical methods is beneficial to critical aspects of design such as analysing keyblocks that would be exposed during excavations. The detailed characterization of block size and shape is also a step toward interpreting the kinematics of rock mass deformation and the analysis of rock masses as ultra-close packed dilatant granular systems.