Innovation of digital geotechnical mapping techniques in underground excavations with the Mapper

Josephine Morgenroth, our Research and Technical Partnerships Manager at RockMass Technologies applied the new trace discontinuity mapping function of the Mapper to Rio Tinto’s drill and blast and Tunnel Boring Machine (TBM) tunnels at the Kemano hydroelectric facility near Kitimat, Canada with the help of the geotechnical and tunnel engineers at Hatch.

The construction of this project involves excavating a TBM tunnel through the Coast Mountains of British Columbia, which is a highly technical and logistically impressive feat. The challenging nature of the project site requires innovative technologies (and people!) to ensure its success. Mapping of geological structures in the tunnels, as well the subsequent generation of as-built drawings, is a crucial step in the evaluation of excavation performance during and after tunnel construction.

Josephine Margaroth Undergroun Tunnelling Boring MachineJosephine’s case study involved a comparison of conventional mapping methodologies, typically a tedious paper-based process, with our digital mapping solution. In conventional mapping, geotechnical data is collected manually and then transcribed to a compatible format based on the software that is being used for post-processing or visualization.

The new trace discontinuity mapping method was performed at Kemano and compared to conventional compass measurements, as well as RockMass’ existing 3-dimensional Axis Mapping (3DAM) method to provide a basis for comparison across several methods of data collection and to compare accuracy.

Trace discontinuities present a challenge during typical geotechnical mapping exercises, as they do not have much (if any) exposure and their orientation is generally estimated using a compass and visual inspection. In larger drill and blast and TBM tunnels, traces may also be difficult to reach or estimate visually. Following the method set out in 3-D Structural Geology: A Practical Guide to Surface and Subsurface Map Interpretation (Groshong, 1999), the orientation of a geological feature can be calculated if the coordinates of three points on its surface are known.

Combining this with the georeferenced point cloud captured by the Mapper allows users to take a scan of a tunnel wall or face, select three points along with a trace feature, and automatically calculate its dip and dip direction. This method of trace orientation calculation takes a matter of seconds.

The study at Kemano showed that using the Mapper to capture trace discontinuities in TBM and drill and blast tunnels obtained more accurate geotechnical data in a digital form, allowed for quicker data capture and analysis, and can result in more reliable excavation design in the long term.

Stay tuned for our upcoming publication in the EUROCK 2022 proceedings where we will release the full outcome of the case study.