3-D DIGITAL ROCK MASS DISCONTINUITY CHARACTERIZATION USING HIGH-RESOLUTION PHOTOGRAMMETRIC OR LASER SCANNER POINT CLOUDS

Both digital photogrammetry and laser scanning can be used to characterize hydrogeologically or geomechanically important discontinuities in natural outcrops, quarry or mine walls, and roadcuts. Point clouds produced by either method characterize rock exposures using tens of thousands to hundreds of thousands of x-y-z values that can be referenced to any geographic coordinate system and manipulated to extract information on the number, mean orientation, and orientation variability of discontinuities. One approach is to identify individual planar elements and calculate their orientations by fitting planes to the points that comprise each element. This is a virtual version of traditional geologic fieldwork in which the geologist identifies each significant surface, measures its orientation, and plots the result using a lower hemisphere projection. A complementary approach is to create a triangulated irregular network (TIN) among the points and assume that the resulting triangles represent portions of geologically significant surfaces such as faults or joints. The orientation of each triangle can be calculated as the numerical solution to a three-point problem and the results plotted on a lower hemisphere projection for analysis and interpretation. In cases where clusters of diplines or poles represent sets of systematic discontinuities, each triangle can be assigned a cluster membership and the results mapped onto a 3-D rendering of the TIN to visualize the discontinuities. Clusters can be identified using either qualitative interpretation or statistical techniques such as hard or fuzzy cluster analysis. As illustrated in this presentation, k-means cluster analysis can be supplemented with human judgement to create detailed and geologically realistic models of discontinuity distributions in structurally complicated rock masses.