Use of 3D Laser Scanner for Rock Fractures Mapping

Abstract

In the process of investigation, design and upgrading of rock slopes, the orientation and spacing of the structural discontinuities or joints in the rock mass are thoroughly mapped in the field so that any unstable blocks can be identified and stabilization measures designed. The orientation of the structural discontinuities is traditionally measured manually using geological compass placed directly at the exposed surfaces. Scaffolding is usually erected so that the geologist can physically access the exposed rock surface. A large number of measurements are usually required in order to obtain a statistical mean of the fracture orientation. With the ongoing advances of digital technology, 3D laser scanning technique can be used to replace direct physical access and large number of manual measurements can be completely eliminated. A prototype system is described in this paper that combines the non-contact measurement technologies of photogrammetric imaging and 3D laser scanning to create dimensionally accurate and pictorially correct 3 dimensional models and orthoimages of a rock fractures. By taking photographs from at least two different locations, lines of sight are mathematically intersected to produce the 3D coordinates of the key reference points in a rock face. Automatic 3D laser scanning unit is then used to produce the 3D coordinates of the entire rock surface. By overlapping the images rectified from photogrammetry technique with the coordinates from 3D laser scanning in an Autodesk 3D Studio Max environment, the coordinates of any objects in the photographs can be selected and their orientation such as dip angle and dip direction calculated automatically. A case study is presented to compare the orientations of fracture planes measured using geological compass and the orientations from the prototype system developed.