3D geological modelling in support of underground mining industry

The present paper describes a working approach that involves the combination of Terrestrial Laser Scanning (TLS) and traditional geological surveys for creating the three-dimensional model of an underground quarry located on the Apuan Alps (Italy). The final model includes information on the geological structure and marketable marble varieties. TLS can be used to obtain detailed and accurate geometrical information in short working times by generating several point clouds that can accurately model the detected surfaces. The study area comprises a network of tunnels, for a total length of about 140 meters, and 20 different scan positions were necessary to cover the entire area. In order to register all the point clouds data to a unique reference system, a topographic survey was conducted. The coordinates of some optical targets, positioned at specific locations within the excavation area, were measured by employing a Total Station and two GPS receivers. Differential GPS surveys and post-processing procedures have guaranteed a sub-centimetric accuracy of the targets and, consequently, of the point clouds. From the 3D use of the data, the new topographic map of the quarry was generated at a scale of 1:500, and several 2D cross sections were created for better understanding of the quarry's actual scenario. The structural and morphological limits of the quarry surfaces were restituted directly from the point cloud data. Further, “non uniform rational basis-spline” surfaces (NURBS) were created by employing a specific modelling software, which allowed to create the 3D model of the quarry. The application of NURBS surfaces, instead of meshes has turned out to be a better option in terms of speed, accuracy, control of operations and for the requirement of powerful compute. Detailed traditional geological were carried out and a new geological map including the marketable marble varieties was created. Five detailed geological cross sections were drawn by combining both surface and sub-surface data. Finally, the 3D geological model of the area was generated. The combination of the two models has helped in understanding the relationship between quarry and marble deposit and it allowed to make exact measurements of distances and to quantify the extractable marble volumes. The present working approach can be adapted in different geological contexts, since it allowed to obtain a huge amount of data in short working times without sacrificing details and accuracy. Such properties make of it an important instrument to improve cultivation plans for both safety and commercial reasons.