Tunnels facilitate first UK curved jacked-box structure

UK-based Morgan Sindall broke through on the second of two tunnels on Network Rail’s Werrington Grade Separation project, on 1st August 2020. Boosting around 7 meters per day, a Lovat RM132 3.5 m-diameter EPB machine has excavated two guide tunnels. The tunnels form a part of an ambitious civil engineering project that will see installation of the UK’s first-ever curved jacked-box structure.

Mott MacDonald and Tony Gee have done the engineering design for the project, and Tunnelcraft has supplied the specialist labor.

The project which is located at north of Peterborough, is part of the £1.2bn East Coast Upgrade, which intends to facilitate faster journeys between London and Scotland and increase train capacity. The ‘dive under’ will allow two new tunneled rail lines to pass under the East Coast Main Line (ECML), as a result separating freight traffic from high-speed passenger trains. This will remove a major traffic jam from a nationally-important rail line.

The segmentally-lined 155m-long tunnels, located about 7m below ground in clay soil, will operate as a guideway for the dive-under structure – a curved, large, insitu-poured concrete box which will be installed below the East Coast Main Line. Tunneling under live rail lines dictated the use of an EPB TBM to downgrade surface settlement.

Once the soil above the tunnels is removed, specialist firm Jacking Structures will start pushing the box into position. At the moment, being constructed beside the railway, the concrete box with 155m length, 9.5m width and 5.1m height will be pushed into place on guide rails installed inside the tunnels. As jacking progresses, the box will break out the top third of each tunnel. Once in place, the 1m-thick 11,000t structure will sit above the tunnels which are designed as permanent as they will provide temporary support for the box until backfilling and other supporting structures are in place. It is expected to have the box jacking into position nearly in fall 2020.

Source: Tunnels and Tunneling