Box sliding has been used on the railways before, but according to HS2 this will be the first box slide of its kind over a motorway in the UK.
BBV will construct the 10,000 tonne bridge box – a base, walls and top slab – on land next to the motorway. It will then be slid into position.
The bridge was originally designed as a traditional structure, which would have meant two years of motorway lane width reductions, 50mph speed limits and weekend and night closures.
The box slide method means only two one-week closures of the motorway over a 12-month period. It also means the workforce does not need to work in such close proximity to a live carriageway for so long.
BBV has started preparing for the construction of the Marston Box bridge near Junction 9 of the M42 in north Warwickshire. The M42 will be closed for one week for the first stage of preparation work between Christmas and New Year 2021, with plans to move the structure into place during a week’s closure in winter 2022.
During the one-week motorway closure this Christmas, the team will remove the motorway surface, excavate approximately three metres deep across the footprint of the structure, remove a redundant fuel pipeline, and remove an existing drainage system and reinstall it elsewhere. Ground improvements will also be made in preparation for the box slide.
Two tower cranes will be erected next to the motorway to service the construction of the guide raft and the box structure in early 2022. The guide raft, a reinforced concrete slab, will be constructed first and then the box constructed on top. It will be a reinforced concrete box structure with base, three walls and top slab, with part of the jacking mechanism cast into the base of the box.
The box slide itself involves a jacking system designed by specialist contractor Freyssinet, which will push the box across on the guiding raft. Once moving, the box can reach speeds of more than two metres per hour, so the whole operation of the box slide should only take four days, with a week closure required for the preparation, box slide and re-opening of the M42. That’s the plan.
David Speight, client project director at HS2 Ltd, said: “At HS2 Ltd we’re always looking for innovative ways to reduce our impact on local communities, and this UK-first ‘box slide’ provides a quicker and safer solution. We’re working very closely with National Highways to ensure traffic management plans are in place, with a clearly signed diversion route to minimise any impacts during the motorway closure.”
BBV site agent Chris Hurrell said: “Through forward-thinking methods such as the ‘box slide,’ we are able to significantly reduce disruption for the travelling public, using the skills and expertise of over 100 of our people across a range of disciplines, to cut the motorway closure period to just two weeks over a 12-month period.”