Construction of new road access below one of the UK’s busiest freight railway lines demanded careful oversight to ensure the planned closure did not overrun.

  • Owner
    Highways England
  • Client
  • Delivery date
  • Engineer

Key figures of the operation

A contract to improve highway access to the port of Immingham in the east of England included the creation of new links into the existing road network. As part of this, a two-lane highway bridge had to be installed below the railway that serves the port, widening the existing access.

Sliding a reinforced concrete bridge box, measuring 39x18x11m high, utilising Freyssinet Autofoncage® method required the use of four 1,000 tonne strand jacks and associated hydraulic equipment to move the structure. To ensure a successful operation, the system was tested 48 hours before the main slide.

  • 3,750t
    Weight of new bridge (tonnes)
  • 41m
    Distance the bridge was moved (meters)
  • 3.4m/h
    Speed of bridge sliding (meters/hour)
Immingham bridge UK underpass

Minimising down-time

Disruption of this vital supply route had to be kept to a minimum, hence a 76-hour blockade was scheduled to take place during the Christmas break. Planning began several years ahead of the line closure, at which time Freyssinet’s Autofonçage® bridge sliding technique was identified by scheme designer Jacobs as a good fit for such a time-sensitive operation.

Forward planning

In the Autofonçage® procedure, the new structure is built offline, but adjacent to its final position, before being ‘floated’ into place on a bed of bentonite. Live jacks at the rear of the structure push it towards the embankment along cables that are recessed into channels in soffit of the base slab of the box, and attached by passive anchors to the raft at the end closest to the railway. Final trimming of the earthworks can continue at the leading edge of the structure while it is being jacked forwards.

Immingham bridge UK underpass
Immingham bridge UK underpass

Offline advantage

This technique has major advantages over the traditional alternative of piling and excavating – which is very crane-dependent and easily impacted by poor weather – and even over other bridge sliding techniques.

Its key benefit lies in the fact that all preparatory work for the slide can be done with the railway line open, as temporary works do not encroach on the embankment.


The elimination of crane-dependent operations worked strongly in the project team’s favour when the planned rail possession coincided with the worst UK winter for some years. In these circumstances, the value of the extensive contingency planning that had preceded the closure became apparent.

When the embankment showed signs of becoming unstable due to the extremely heavy rain, the team had the right equipment on hand to remove the loose material and trim it back to a stable profile.

Immingham bridge UK underpass
Immingham bridge UK underpass

European standard

The operation at Immingham was only the second time the Autofonçage® procedure had been carried out in the UK, although Freyssinet had been using it widely in Europe for two decades.

Work started on Christmas Eve after the railway line was closed at 22.00 hours, with rails being removed and the embankment excavation following on. The box slide began at 9pm on Christmas Day and despite the weather, took less than 12 hours to complete, enabling the railway to be reinstated and the blockade lifted within the planned schedule.

Risk reduction and contingency planning meetings started in the design phase, two years before the box slide. Initially, Freyssinet contributed to Jacobs’ risk register, which was subsequently adopted and developed by Costain. We became an important part of the integrated project team, attending specific risk meetings with Costain and their other subcontractors.

Our contribution was highly valued, especially by the earthwork’s contractor. Costain invested time developing ‘what if’ scenarios with the supply chain and, collectively, contingency measures were identified.

Project manager, Freyssinet UK

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