Issue link: https://geospatial.trimble.com/en/resources/i/1480682
Change in plan Tunnel surveying is a specific breed of project that requires unique techniques and skill sets. It's challenging to create and manage a geodetic control network, operate in a GNSS-restricted environment and maintain high accuracy over a long, linear distance underground. It also requires a solid understanding of geodesy to anticipate how the vertical alignment of the tunnel is affected over its length. Not only do the Maursund and Kågen tunnels have these general complexities, they have multiple layers of challenges in addition to the 24/7 traffic flow issue. Neither one has been designed with a pre-defined shape, making it more difficult to guide construction. All the rock material that is extracted is immediately reused by other firms so there isn't the option to measure stocks and calculate volumes. None of the machinery—save one grader with a Trimble SCS900—is equipped with machine control. And in the Maursund tunnel, a technical building, measuring 5.4-m wide, 4-m high and 19-m long, needed to be constructed and assembled into a confined space with a tolerance of 0.5 m. When the renovation first began in January 2021, the original plan was to run one, two- person survey team with a total station and occasional scanning, and they would alternate every week. However, given the scale, seing and project deadlines, this approach proved problematic within the first two months of work. "Measuring and establishing control for the carriageway—one of the most essential jobs to ensure we create the required width and height—with a total station requires constant seing up, measuring and seing out, which is quite time consuming," says De Vuyst. "So in order to keep up, they had Drilling out space for Maursund's technical building. On the rig's screen the operator can see the driving box to help guide the drilling. Above: Viewing two scans on the TSC7. The smoother green scan captures a section of the Maursund where reinforcement materials have been installed. The rougher red one doesn't yet have reinforcements installed. Center: The SX12 outside the Maursund tunnel. The American Surveyor / July/August 2021 20