Modeling a Shallow Rock Tunnel Using Terrestrial Laser Scanning and Discrete Fracture Networks

Discontinuity mapping and analysis are extremely important for modeling shallow tunnels constructed in fractured rock masses. However, the limited exposure and variability of rock face orientation in tunnels must be taken into account. In this paper, an automatic method is proposed to generate discrete fracture networks (DFNs) using terrestrial laser scanner (TLS) geological mapping and to continuously calculate the volumetric intensities (P32) along a tunnel. The number of fractures intersecting rectangular sampling planes with different orientations, fitted in tunnel sections of finite lengths, is used as the program termination criteria to create multiple DFNs and to calculate the mean P32. All traces and orientations from three discontinuity sets of the Monte Seco tunnel (Vitória Minas Railway) were mapped and the present method applied to obtain the continuous variation in P32 along the tunnel. A practical approach to creating single and continuous DFNs (for each discontinuity set), considering the P32 variations, is also presented, and the results are validated by comparing the trace intensities (P21) from the TLS mapping and DFNs generated. Three examples of 3DEC block models generated from different sections of the tunnel are shown, including the ground surface and the bedrock topographies. The results indicate that the proposed method is a practical and powerful tool for modeling fractured rock masses of uncovered tunnels. It is also promising for application during tunnel construction when TLS mapping is a daily task (for as-built tunnel controls), and the complete geological mapping (traces and orientations) is available.