Morgan Sindall has pushed an 11,000t curved concrete box into place under the East Coast Main Line near Peterborough, in what was claimed to be a UK engineering first.
The tunnel at Werrington, which will enable slower-moving freight trains to pass underneath the passenger route and use an adjacent line northwards, was installed over nine days this month.
The 155m curved concrete box tunnel, which is heavier than the Eiffel Tower, was eased into place at a rate of 150cm per hour, using four hydraulic jacks.
Teams removed three of the tracks, lifted the overhead wires and dug out spoil from the site. Once the tunnel was eventually underneath, they then put everything back in place ready for regular services to resume.
The next stage of the project at Werrington, part of the £1.2bn East Coast Upgrade, involves work to install two new tracks inside the new tunnel and the associated signalling system, ready for it to come into use at the end of 2021.
Paul Rutter, route director for Network Rail’s East Coast Route, said: “Our teams have completed this challenging piece of engineering in a creative way, which also allowed a reduced train service to continue for those who still had to travel.
“Over the nine days, we’ve made major progress on this vital project which will bring faster, more reliable journeys for passengers on the East Coast Main Line.
“I’m so proud that this project has shown itself to be one which is industry leading and that our teams have had the opportunity to use this new technique for the first time in the UK on one of the country’s most famous railway lines.”