UK’s first ‘box-slide’ bridge to run over M42

Architect’s impression of Marston Box rail bridge over the M42

Joint venture company Balfour Beatty VINCI (BBV) is to build the UK’s first ‘box-slide’ railway bridge over the M42 motorway in North Warwickshire.

The railway bridge will carry HS2 passenger trains north to Crewe and south to Birmingham, as well as onward destinations such as the new Interchange Station in Solihull or London Euston.

Project leaders have decided to use the 10,000 tonne box-slide bridge structure in order to minimise disruption to motorway users during construction. 

David Speight, Client Project Director, 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.

The bridge was originally designed as a traditional structure, however this “would have meant significant traffic disruption for motorway users, with around two years of reduced lane widths, 50mph speed limits and weekend and night closures,” HS2 Ltd said.

The new ‘Marston box’ bridge structure, which comprises a bass, three walls and a top slap, will be built on an area of land next to the motorway.

According to HS2 Ltd, once construction of the box bridge is complete, a “hi-tech raft will then glide it into position” in single movement.

Employing the box-slide method - which has the added benefit of keeping construction workers safe as they do not need to work close to the M42’s live carriageways, as would be the case when building a traditional bridge - will mean that the M42 will only have to be closed twice over the course of 12-month period.

“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,” said HS2 Ltd.

BBV is currently preparing for the bridge’s construction near Junction 9 of the motorway in North Warwickshire. 

These works will see the contractor will remove the motorway surface, excavate the ground to approximately 3m deep across the footprint of the structure and remove a redundant fuel pipeline and an existing drainage system.  

Two tower cranes will also be assembled on the site. These will be used to help site workers “service the construction of the guide raft and the box structure in early 2022”.

While the structure of the guide raft will be comprised of a reinforced concrete slab, part of the jacking mechanism - which was designed to “push the box across on the guiding raft” by engineering company Freyssinet - will be cast into the base of the bridge itself.

According to HS2 Ltd, the process of installing the bridge using the guide raft will see it reach speeds of over 2 metres per hour, “so the whole operation of the box slide should only take 4 days”.

BBV will carry out both preparatory works and the box slide itself during the second week-long closure of the M42, which is currently expected to take place in the Winter of 2022.

Speaking of the upcoming motorway closure, Frank Bird, National Highways Senior Network Planner, said, “We’ve been working closely with colleagues at HS2 Ltd to plan this closure over the Christmas period when we know that major A-roads and motorways are quieter.

“While we appreciate this closure will cause some disruption on this part of the M42, we’ll be lifting and completing hundreds of miles of roadworks across the country between Christmas and New Year to help keep traffic flowing.

Appealing to drivers who use the route, he said, “We’d encourage all motorists to familiarise themselves with the diversion route before setting off and to leave additional time for their journeys.

“We’d also like to remind people about the importance of checking their vehicle before setting off on their journeys.

“Simple things like checking your fuel and oil levels, tyre pressures and that all lights are working properly, can keep you moving and the network flowing.”