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Case study

Replacing a railway overbridge within severe time limitations

18 September 2017

Self-propelled modular transporters: number of advantages over using a crane

Replacing a railway overbridge within severe time limitations
Self-propelled modular transporters: number of advantages over using a crane

In 2013 a routine inspection of the Network Rail owned bridge (TCC 27A) carrying Awsworth Road, Ilkeston, over the operational railway identified severe corrosion to the north parapet steel girder.

The triple-span TCC 27A had an eventful 116 year history including two separate train strikes and being raised by over a metre. But the 25m bridge was now beyond economic repair and required full reconstruction.

With limited rail access leaving just 29 hours to demolish and replace the bridge deck, a collaborative team from Network Rail (NR) and AMCO used careful planning, innovative methodology and an emphasis on safe working practices to achieve successful project delivery.

Old brigde needing replacing
Old brigde needing replacing

Minimising rail network disruption

Aiming to minimise disruption to the rail network, the actual demolition and replacement of the bridge deck was planned for completion in a single train-free 29-hour operation in December 2016. Not only was this a short amount of time for such a complex scheme of work it was also a fixed date booked a year in advance that could not be rearranged without significant delay and cost. Detailed planning and prioritisation was crucial.

Preparatory works began onsite in September 2016. The road was closed to traffic and a compound was created on land leased by Ilkeston Juniors Football Club. The changing rooms were relocated by AMCO in order to minimise disruption to the club's scheduled practices and matches.

Prioritisation of works

Priority works were those that could not be completed once the new bridge deck was in place. The highest priority was the construction of the new deck on trestles in the compound. 250 tonnes of weathering steel were delivered to site and an equal weight of reinforced concrete cast on top and left to cure.

This produced a single span 33m bridge deck which HBPW designed with longevity in mind. Alongside this the parapets of the old bridge were removed, the approach road was excavated to create a horizontal working surface and the abutments were reduced to the desired post-installation level. Auger piling was then undertaken to enable construction of new bankseats on which the longer, wider deck would sit.

Challenges in preparatory works

The preparatory works were themselves not without challenges. Extensive probing successfully identified that the many bell pits in the heavily-mined area were unlikely to hamper the major works but ground conditions slowed construction. The auger pile bores filled with more water than anticipated.

In addition, a power cable conflicted with the planned works but was only identified once onsite as the power company had recorded it in an incorrect location.

Solutions included a back-up piling rig and relocating the cable

Both of these issues were solved by the highly experienced NR-AMCO team. A back-up piling rig was one of many contingencies anticipated in the planning stages and collaboration with the power company identified a safe way to relocate the cable to allow works to continue.

These and several other quick thinking solutions from the project team meant that the preparatory works were completed well in advance allowing everyone to focus on the innovative plan that had been developed for the 29 hour operation.

Installing the bridge replacement

New bridge after construction
New bridge after construction

Unlike most bridge replacements the old and new decks were moved using self-propelled modular transporters (SPMTs), rather than lifted by cranes. Despite many of the project team being unfamiliar with SPMTs, using these innovative machines had three benefits: precious time would be saved, wind susceptibility was significantly reduced and a nearby pond was spared from being infilled to accommodate a crane - thereby reducing the environmental impact of the project.

The size of the compound made manoeuvring the bridges a challenge. AMCO produced phasing diagrams and carried out trial drives to refine plans and provide assurance of success. Crucially, this identified that one of the temporary supporting trestles for the new bridge had to be completely removed to provide room for the SPMTs to drive the deck onto the track.

Removal began at 9am. New deck landed 8pm

With both NR and AMCO team members onsite the old bridge removal began at 9am. Three SPMTs were used to lift the old deck and move it to trestles in the compound. Two of these then realigned to lift the new bridge into place while the old bridge's supporting piers were dismantled.

The new deck landed at 8pm, with the whole operation completed after just 20 hours, including the placement and removal of track protection measures.

Lessons learned

After significant follow-up works the road reopened to traffic in April 2017 and reconnected Ilkeston town to Awsworth village. After the main works a full team meeting (including NR, AMCO and the main subcontractors) identified several lessons that can be learned including refined procedures for works with a critical date and suggestions for subcontractors to improve safety when removing bridges with SPMTs, by creating "moving exclusion zones".

Such lessons will be taken forward to future construction projects, improving site safety and project success rates.

New bridge: better access, visibility and safety

Local businesses and residents now have better aligned road access and a wider carriageway, meaning increased visibility for drivers and safety benefits due to room for a pedestrian footpath.

The new bridge deck is designed to last for 125 years providing both the people of Ilkeston and railway users with a safer, stronger structure for the future.

The success of this project is ultimately down to an effective working relationship between Network Rail, AMCO and their multiple subcontractors.

Close collaboration, open communication and sharing of expertise not only enabled the use of innovative technology to deliver a complex, time-limited bridge reconstruction, it also led to the production of a highly viewed time-lapse video that has generated great publicity for the civil engineering profession.

Project details

Location: Ilkeston, Derbyshire
Value: £3 million
Date of completion: April 2017
Duration: 8 months
Client: Network Rail (NR)
Contractor: AMCO
Subcontractors: HBPW, Martello Piling, ALE, 1st in Rail
Project manager: Chris Chatfield (NR), Dave Millar (AMCO)
Challenge summary: Full reconstruction of a failing railway overbridge with severe time limitations.
Challenge solution: Utilisation of a collaborative approach and innovative technology to ensure successful project delivery.

New bridge in place
New bridge in place

New road over the bridge
New road over the bridge

  • Emilie Brignall, Network Rail