Lighting the Way By Mary Jo Wagner
When professional surveyor Sylvia De Vuyst ar - rived in the northern edges of Norway in March 2021 for a significant tunnelling project, she wasn’t sure what to expect. Freshly hired as the tunnel surveying manager for Mesta, a civil engi - neering construction company based in Lysaker, Norway, De Vuyst would be the lone surveyor responsible for the NOK $211 million (US $24.8 million) renovation of the Maursund and Kågen Tunnels, two critical passageways that connect the cities of Nordreisa on the mainland and Skjervøy on Kågen island. Each about 2 kilometers long, the Maursund Tunnel (Maursund) travels under the North Sea, reaching a depth of −92.5 meters (−303 ft) below sea level and a 10-percent grade in some areas; the Kågen passes through Kågen mountain, which is vulnerable to avalanches and landslides. Built in 1991, both structures will undergo extensive upgrades including widening their carriageways, installing new LED lighting, Co / No2 gas meters, new water and frost protection, and new drainage systems, and building new road surfaces. After one week in the dark, damp tunnels, one project requirement became abundantly clear to De Vuyst: she’d need to be agile. “A major challenge with the Maursund is that it needs to stay open 24/7 to allow traffic to pass through at set times,” says De Vuyst. “This means that many times a day the diggers and bolt riggers need to move to the side, big trucks need to drive out and sometimes I need to stop my survey work. So when we’re clear to work, we have to maximize our productivity. To ensure construction stays on target and pace, I need to be efficient, reliable and precise.” Instead of using the traditional total station––the typical domain of tunnel surveys––De Vuyst opted to replace convention with a scanning total station. Combining the high accuracy total station point measure - ment with the speed and precision of 3D scanning, De Vuyst is manag- ing two tunnel environments where tolerances are tight, space is at a premium, visibility is low and expectations are high––on her own. And she’s matching the frenetic pace of the digging, blasting and bolting at six times the speed of multiple-person crews. 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 geo-
detic 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,
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November 2021 csengineermag.com
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