Applying photogrammetry and semi-automated joint mapping for rock mass characterization

Rock engineering in blocky rock masses demands a sound knowledge about the joint network, since it consists of planes of weakness than can lead to block instabilities. However, collecting data about the joint network is time consuming, seldom very detailed and depends strongly on the experience of the mapping geologist. Additionally, the characterization is reduced to the identification of the most relevant joint structures with their characteristic orientation and spacing. Other parameters, like the in situ block shape and the block size distribution or the main orientation of the blocks are seldom collected or determined, if at all. With the emergence and increasing application of digital surface mapping techniques in rock mass characterization, like ShapeMetriX^3D or the Discontinuity Set Extractor, the time needed on site could be reduced and the degree of detail in the mapping of discontinuities is improved significantly. The work presented in this study displays a continuous work flow from the data collection in the field to the determination of the block size and shape distribution, generated by the intersection of joint sets. For the process, a marble quarry in Styria (Austria) was digitized, using photogrammetry. The joint sets are semi-automatically identified with the Discontinuity Set Extractor whose results are transferred into the software ShapeMetriX^3D, where the joint set spacing along with its standard deviations are determined. These parameters are used to generate statistical representation of representative rock mass units, using 3DEC (Itasca Consulting Group, Inc.) and determine the block sizes, block shapes and main orientation of the blocks in a row of simulations.