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Crowning glory

King's Cross

In advance of Tube Ticket Hall construction, contractor Gleeson MCL sliced the crown off a section of the Thameslink running tunnel, which runs beneath the edge of the Tube Ticket Hall on the north side of the Euston Road.

The railway line was closed completely for five days during Christmas 2002 to allow the contractor to slice off a 10m length of the tunnel crown and replace it with the steel and concrete composite roof that will form the floor of the new ticket hall above.

Gleeson - working as subcontractor to CTW - initially installed a temporary structure around the tunnel in advance of the closure. Ground above the shallow tunnel crown was excavated - leaving enough fill to maintain the tunnel's arch action - and large pits dug either side of the tunnel walls and filled with concrete to form buttresses.

Steel columns were cast into the concrete and linked by props to create figoal postfl frames around the 10m length to be removed. These were designed to prevent the tunnel walls being pushed inwards when the crown was removed.

During the closure, which started on Christmas Day, the contractor erected a crash deck in the tunnel, dismantled the existing crown and installed the composite roof structure.

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