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St Pancras remains critical path

Reconstructing and refurbishing the Grade 1 listed St Pancras Station Barlow train shed is the project's single most significant critical path operation.

The fragile condition of the Victorian landmark means that engineers cannot be entirely sure what awaits them as work on the structure advances, and for Dyke this is a worry and a major challenge. He already has as much labour and equipment working on the congested site as is physically possible. If nothing unexpected happens he will just make the programme.

Yet, realistically, he is aware that it is unlikely nothing new will crop up.

'We have lost time on the refurbishment of the train shed due to its complexity and condition, ' he admits. 'It is being delivered at a cost and there are still considerable areas of risk.

'We can commission the railway up to the platforms while the station is still being completed. But our ability to predict the progress rate of the refurbishment of a Grade 1 listed building is not as secure as new building work, ' he adds.

Getting to the point where the train shed can be prepared for Eurostar trains has taken the best part of three years. A new station has had to be created alongside the original into which train services to the Midlands and beyond have now been transferred. This is contained inside one half of the final train shed extension.

The second half of the train shed extension will begin in earnest on completion of the new Thameslink station box beneath the site (NCE 16 September 2004). This massive operation has interrupted the Thameslink north-south throughservice for seven months. The box and track are on schedule to be handed back to Network Rail allowing through-services to restart next month.

Extending the train shed is a breeze compared with work now under way on the original structure. Its in-situ concrete track deck is supported on a forest of cast iron columns and wrought iron beams and deck spans. This deck is being replaced with a new reinforced concrete deck capable of taking higher train loadings.

Although load will be carried by the original columns, the fragile wrought iron beams must remain load free. So the new deck is being poured using special jacked formwork which lifts the slab clear of the existing structure. It is then lowered onto new bearings mounted on the column heads (see diagram).

'The condition of the train deck has given us problems, ' says Dyke. 'We are trying to retain a lot of the existing fabric but it does not fit easily into a modern design code analysis so a lot of unique work had to be done.' On the up-side, Dyke says that deteriorated areas of the structure have now been identified, and work to repair them is under way.

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