Radlett Freight Interchange Project Completes 6,000T Bridge Slide Under Midland Main Line

The Radlett Strategic Rail Freight Interchange (SRFI) project in Hertfordshire reached a significant milestone in December with the completion of a complex box slide involving a 6,000t bridge structure.

This operation was conducted beneath the Midland Main Line rail network near St Albans, forming part of a broader initiative to create a new rail-to-road freight depot on the site of the former Radlett Aerodrome.

The development is aimed at enhancing freight transport connections and requires the establishment of a new rail link to the Midland Main Line. This involves constructing an embankment and an underbridge that will enable the new rail chord to travel beneath the existing four tracks of the Midland Main Line.

Principal contractor VolkerFitzpatrick spent nine months constructing the cast in-situ underbridge next to the rail line.

The process involved cutting out a 60m section of track and removing approximately 12,000m3 of soil from the 19th century rail embankment to make space for the structure.

To move the underbridge, VolkerFitzpatrick utilised Freyssinet’s innovative Autoripage technique. This method involves pre-casting the structure on a guiding raft adjacent to the operational railway and lubricating it with bentonite liquid clay, allowing for a smoother sliding process into position.

This approach not only minimises disruption to rail services but also enhances safety by segregating construction activities from live rail operations.

The permanent structure measures 61.38m long by 16.55m wide. The temporary guiding raft measured 79.6m in length and 17.37m in width.

The sliding operation was executed during a scheduled rail blockade over the Christmas period.

A pre-slide test was conducted on 20 December 2024. This was followed by the main sliding operation which commenced at 4.58pm on 22 December and concluded at 5.20am on 23 December, meaning it was successfully completed in just 12 hours and 22 minutes – three hours faster than originally planned. This efficiency highlights the collaborative efforts of Freyssinet UK, VolkerFitzpatrick and other partners involved in the project.

The total sliding distance was 62.5m, using 46 strands per cable and a sophisticated hydraulic jacking system comprising 12 jacks.

The average sliding speed observed was approximately 5m per hour, with peak speeds of around 15m per hour.

Watch a timelapse of the operation below.

The underpass is essential not only to enable further works on the project but will also carry the two road rail line feed into a new rail terminal area and allow the construction of the associated warehousing.

The Radlett SRFI is being constructed on behalf of Segro, which will own the new interchange to serve the Midland Main Line railway via a new two road rail connection.

The multi-million pound development also incorporates a new underpass as well as overhead line equipment works, lineside civils, installation of switches and crossings for the main line connection and signalling.

The Radlett SRFI represents a critical investment in the UK’s freight transport infrastructure, likely to boost efficiency in logistics and distribution while showcasing advancements in construction technology.

It will be one of 20 SRFIs in the UK and the only one serving the London area. It will span approximately 405ha, incorporating 335,000m2 of advanced, highly sustainable logistics warehouse space, enveloped in 240ha of managed woodland, conservation grazing and public country park.

New underbridge structure successfully installed beneath Midland Main Line

VolkerFitzpatrick divisional director, rail and depots Paul Lilley said: “This milestone marks a significant achievement for VolkerFitzpatrick and showcases our commitment to delivering complex infrastructure projects with precision and care. With an unprecedented tight schedule to deliver over a nine day period, the successful installation of the underbridge is a testament to the teams meticulous planning, technical expertise, and the dedication. We are proud to contribute to a development that will leave a lasting positive impact on both the local community and the national supply chain.”

Segro senior director Charles Blake said: “The successful installation of the jack box is a critical first construction milestone in the development of the SRFI at Segro Logistics Park Radlett, and the result of months of meticulous planning, preparation and delivery to ensure it could be completed during the Christmas period when the railway was already scheduled to be closed.

“In the context of the wider development it is a relatively small component, but it is vitally important to ensuring that the freight terminal will be capable of operating by the time the first building has been constructed and reinforces our commitment to rail freight being at the heart of this development.”

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