Methods of automatically extracting rock discontinuity orientations from digital images and 3D models generated using current laser scanning technology are under development. Using a series of image processing algorithms, fracture traces can be delineated from digital images of exposed rock surfaces and in turn, used to determine discontinuity data. Field studies suggest that the discontinuity data collected from digital images compares favorably to data collected using more traditional manual methods. Algorithms for the processing of raw point clouds, created by laser scanning exposed rock surfaces, have been developed. A novel method of triangular mesh generation rapidly creates a 3D model of the scanned surface. The triangular elements of the mesh are grouped together using their normals as a similarity measure, resulting in the identification of larger fracture patches that represent discontinuity surfaces. Refinement and validation of this process has been initiated through a series of field studies. Additional algorithms that expand the application of automated rock mass characterization using digital images and 3D laser scans are under development, with the ultimate goal of creating a software package integrating both technologies and adaptable to any field requiring rock discontinuity analysis.
1. INTRODUCTION
Rock, by its nature, is a complex geologic material and the design of structures in and on rock can be a multifarious problem. Rock engineering is further complicated by the typically discontinuous state of rock masses, where individual elements of rock material are separated by structural discontinuities that include bedding planes, faults, joints, and other types of fractures.
For most rock engineering applications, the material strength of the intact rock between discontinuities is high relative to the expected stresses. In these cases the deformation of the rock mass is generally controlled by the discontinuities, and the behavior of the rock mass, under varying conditions of stress and strain, is dependent upon the nature, distribution, and properties of the discontinuities [1]. These properties include orientation, surface roughness, length, persistence, aperture, spacing, filling, and termination [2]. The most crucial property is orientation (i.e., the direction that a discontinuity is dipping and the angle of its dip), which influences the potential for a rock mass to move, the direction of movement, and the volume of material in motion [3].
There are various engineering situations where knowledge of discontinuity properties is important, and a variety of approaches can be taken in order to analyze the stability and behavior of a rock mass given those characteristics. In mining, discontinuities are central to blast design, blasted fragment size and shape, downstream mineral processing operations (i.e., crushing, grinding, and leaching), open pit slope stability, and the design and stability of underground workings. In civil/geotechnical engineering, collection and analysis of discontinuity data is critical to the design and support of foundations/abutments, dams, tunnels, and road cuts. Likewise, the effect of discontinuities on the stability of underground storage areas and the amount of fluid flow around and through those openings, or in fractures themselves, is of utmost importance in the fields of environmental and petroleum engineering.
