Rapid photogrammetric method for rock mass characterization in underground excavations

Underground excavation mapping and rock mass characterization are critical for ensuring the safety, proper design, and maintenance of underground infrastructure. Traditional mapping methods typically involve manual inspections and measurements that require contact with the tunnel surface, which can be time-consuming, expensive, and pose safety risks to personnel. In recent years, photogrammetry has emerged as an alternative method for generating high-resolution digital 3D models of tunnels, enabling rapid and remote rock mass measurements. In this paper, we present a method for tunnel and stope scanning using photogrammetry and remote rock mass mapping from 3D models. Two case studies are presented to demonstrate the effectiveness of the proposed method. In the first case, a multi-camera rig consisting of action cameras is used for videobased photogrammetric reconstruction of underground tunnel excavation. The rock mass data is then extracted from the model and visualized. In the second case, a drone workflow is used to map out rock mass features in stopes. Images taken with the drone are processed to create a 3D point cloud of the stope, which is then used to extract discontinuities from the rock mass surfaces. The orientation and spacing of these discontinuities are measured and visualized on top of the photorealistic 3D mesh of the stope for inspection. The proposed method significantly reduces the data capture process. The advancements in camera and software technologies have made it possible to acquire rapid and accurate 3D models of underground excavations that can be used as a source of rock mass data. Our results demonstrate that photogrammetry is a robust approach for underground rock mass inspection and remote mapping.