The importance of the collection and analysis of data on discontinuities cannot be overemphasized. Problems which include sampling difficulties, risks, limited access to rock faces and exposures, and the delay in data collection has led to a high need for data collection tools and analysis techniques that can overcome these problems. Great developments have been made towards automated measurements using both optical imaging and LiDAR scanning methods but there is still more room for improvement. Discontinuities manifest themselves as ‘facets’ that can be measured by LiDAR or fracture ‘traces’ that can be measured from optical imaging methods. LiDAR scanning alone cannot measure ‘traces’ neither can optical imaging methods measure ‘facets’. This is complicated by the fact that both ‘facets’ and ‘traces’ are often present in the same rock cut, making the selection of an appropriate measuring tool very difficult if not impossible. In this paper, we present our research on the development of robust software to determine 3-D discontinuity orientations from combined LiDAR and optical imaging techniques.
There are breaks or cracks in every rock mass . Discontinuity is the most general term which suggests a break in the continuity of a rock fabric with no implied genetic origin (Fig. 1a). Discontinuity can be defined as a significant mechanical break or fracture of negligible tensile strength, it has a low shear strength and high fluid conductivity when compared to the rock itself . Discontinuity influences all the engineering properties and behavior of rock . When dealing with discontinuous rock masses, the properties of the discontinuities become a prime importance since that determines to a large extent the mechanical behavior of the rock mass . The presence of discontinuities in a rock mass can affect engineering designs and projects, which include the stability of slopes in a rock mass, the stability and behavior of excavations in a rock mass and the behavior of foundations in a rock mass. The presence of discontinuities also affects rock properties such as the strength of the rock and the hydraulic conductivity of the rock which is responsible for the transportation of groundwater and contaminants . Thus, the importance of the analysis of discontinuities in of a rock mass cannot be overemphasized.
1.1. Rock Falls on Highways Highways that traverse through rocky terrains often require that artificial vertical slopes be cut by blasting techniques to facilitate the highway construction. A constant danger to the motoring public is for large blocks of rock to fall or slide down, at worst killing and injuring members of the motoring public, and at best blocking the highway and impeding traffic flow. Many of these failures result because of release along planar cracks or discontinuities in rock mass. Whether or not failure occurs will depend on the orientation of the cracks, individually or in combinations (Figure 1.1).
1.2. Prediction and Mitigation of Rock Falls The cracks or discontinuities tend to cluster in terms of their orientations, into typically three or more sets, which tend to be mutually orthogonal, or roughly at 90 degree to each other (Figure 1.2). Knowing the orientations of the discontinuities can lead to stability prediction based on well established analytical tools as described by Hoek and Bray .