Characterization of Underground Rock Masses Employing Structure from Motion: Application to a Real Case

Abstract

We propose an inexpensive and easy-to-use methodology for remote characteriza-tion of underground rock masses at the tunnel face. The method is based on the joint use of the Structure from Motion (SfM) photogrammetric technique and a Discontinuity Set Extractor (DSE) software, in which a high-density 3D point cloud is created using a commercial SfM software (Agisoft PhotoScan). To maintain the real features of the tunnel face, such digital model must be orientated and scaled; therefore, a ?portable orientation template? is employed. The point cloud is then introduced in DSE, where discontinuity orientation data are ?extracted? and analyzed to identify joint sets. The measurements obtained with the SfM + DSE approach have been compared with those obtained with a traditional analysis based on manual compass measurements. Both techniques identify the same number of discontinuity sets with orientation differences within the uncertainty range associated to manual measurements.