Pushing a tunnel under railway infrastructure: a timed operation, brilliantly executed by BESIX

Global Me@BESIX Group 2 min read

At Cheratte, in the Province of Liège in Belgium, BESIX is removing two level crossings for Infrabel, the railway network manager, and replacing them with tunnels under the tracks, safer alternatives for local traffic. These are the tracks of line 40, linking Liege and Maastricht, i.e. the east of Belgium and the south-east of the Netherlands. One of the tunnels being installed by BESIX will be used for car and pedestrian traffic. The second, smaller tunnel is dedicated to cyclists and pedestrians.

On the weekend of 18 and 19 September 2021, our BESIX teams had a 53-hour window of opportunity to push and install the main tunnel under the railway tracks. This meticulously planned operation can be seen in full in the video below.

“We previously built the tunnel right next to the tracks. It is an imposing concrete structure, weighing 1,100 tonnes, 14.4 metres long and 7.2 metres high. The operation on 18 and 19 September consisted of pushing it into its final position”, explains Arnaud Fobe, Junior Project Manager at BESIX.

The mass of the tunnel is not the only challenge of the operation. The site itself is unique in that it requires the teams and their machines to work up to 3.5 metres below the level of the nearby river Meuse. The lower part of the site is therefore only dry thanks to a pumping system that operates 24 hours a day.

The third challenge is timing.

“The 53-hour window we had was tight. In concrete terms, the trains had to be able to run one minute before the window opened and one minute after. In between, we had to carry out all the operations, including dismantling the tracks, earthworks, pushing and installing the tunnel, and then completely restoring the railway infrastructure”, continues Andy Gaone, Construction Manager at BESIX.

The success of the operation depended on meticulous preparation and precise planning. The first 4 hours were dedicated to the rail work, including cutting the rails and removing two 65-metre sections of track. This was followed by 14 hours for the removal of ballast and the excavation of 3,200 m³ of soil, plus 3 hours for the dewatering of the excavation and the installation of the pushing system.

“Pushing of the tunnel took place in the late afternoon of Saturday, from 4pm to 9:30pm. The structure had to be driven 25 metres. This is an operation that has to be very precise. The operation is slow and delicate, and at no time did we have the right to make a mistake, from the start to the final positioning”, says Dylan Marichal, Junior Technical Engineer at BESIX.

Next comes the backfilling and load-bearing tests, followed by the actual reinstallation of the railway infrastructure, which includes ballast, levelling, track laying and the various works involved, such as welding.

“In the end, the operation lasted 49 hours and on Monday morning, at 1.30 a.m., the tracks were ready to serve the trains of line 40 again”, says Arnaud Fobe.

Today, trains travel between Liege and Maastricht as if nothing had happened.

“The weather was superb throughout the weekend and many visitors came to take part in the event: local residents, colleagues, families and friends of the various people working on the site. Thank you all for your support”, concludes Sophie Grouvel, BESIX Project Manager.