The construction of a twin-box structure to carry the new high-speed railway, HS2, over motorways in the West Midlands will require the weekend closure of some carriageways, starting at the end of this month.

The first closure will be from 9 pm on Friday, 26th to 5 am on Monday, 29th June, when the northbound carriageway of the M42A will be closed from junctions 5A to 7, and the M6 southbound between Junctions 6 and 7.

The 300-metre-long ‘twin box’ structure, which will span both carriageways of the M42 near Solihull, will enable vehicles to drive through it while HS2 trains travel over the top.

To support the structure, two supporting walls have been constructed on either side of the motorway, and a central pier of 46 supporting columns on the central reservation is nearing completion.

Now that the walls are structurally complete, engineers are continuing with the installation of a beamed roof over the box. This will take place over four weekends between now and September, when 175 prefabricated beams, each 23-metre-long and weighing between 56 and 92 tonnes, are installed. A 300-tonne crawler crane will be used to lift them into position to bridge the gap between the supporting walls and columns.

The new structure will carry four railway lines over the M42, and is between HS2’s Packington and Pool Wood embankments, and less than a mile from the new HS2 Interchange Station to be built in Solihull.

Other major structures to carry HS2 are being built alongside the Water Orton twin viaducts and the M6 South viaduct. Because of the scale and complexity of the operation, National Highways has been closely involved, both with agreeing to the work schedule and setting access dates to the north and southbound carriageways.

“This is a huge moment for the project, and a clear sign of the progress we are making as we begin bridging the gaps over the region’s motorway network. This is British engineering at its very best, and it’s fantastic that a UK-based firm has led the way in developing this innovative design solution for the twin box, with manufacturing taking place in the Midlands.”

Agnes Usciak, HS2 Ltd’s Senior Project Manager for the works