Automated rock mass characterisation using 3-D terrestrial laser scanning

The research that is presented in this thesis investigates the possibility of using point cloud data from 3-D terrestrial laser scanning as a basis to characterise discontinuities in exposed rock massed in an automated way. Examples of discontinuities are bedding planes, joints, fractures and schistocity. Discontinuities divide the rock mass in separate intact rock blocks. The characterisation of the discontinuities in the rock mass is of importance, since they determine to a large extend the geomechanical behaviour of the entire discontinuous rock mass. The conventional way of characterising discontinuities is by manual survey, i.e. geological compass and measuring tape. With the compass the orientation of a discontinuity (dip direction and dip angle) is measured. Orientations are usually plotted in a stereonet in order to identify discontinuity sets. With a measuring tape, discontinuity spacing and persistence is determined. The spacings are usually linked to sets and defined in term of (normal) set spacing. The conventional field methods are simple and effective, but biased, time-consuming and hazardous. Alternatives to the conventional methods for surveying rock faces are two different remote sensing methods: 3-D terrestrial laser scanning and photogrammetry. Both methods yield a detailed 3-D model of the exposed rock face in the form of a point cloud. Laser scanning and photogrammetry both have their advantages and disadvantages. However, the operational advantages and the larger accuracy and resolution that is attainable, makes laser scanning a more attractive field method and is therefore selected as the data acquisition method in this study.