Case study: Station Road, Irchester

Background:-
As part of Network Rail’s wider upgrade of the Midland Main Line, an additional line was constructed between Bedford and Kettering. HBPW was invited to be part of NR’s demolition and bridge upgrade team.

Challenge
The Irchester overbridge, along with another similar structure (the overbridge at Isham) had been identified for a range of demolition and / or upgrade work to pave the way for electric trains.

The question was whether to lower the track level or raise the height of the bridges to make way for power lines. At Irchester whilst the track level could have been lowered, the necessary engineering would have implicated structure foundations as well as a 1,000 metre stretch of line. The area was also prone to flooding and lowering the track at such a late stage, might have affected engineering work already completed to support an additional rail line planned for span four of the five span structure. Then, one of HBPW’s senior engineers discovered nesting brown long eared bats living in the remnants of an old building at Irchester Railway Station!

Solution
The decision was taken to demolish and re-build arch four whilst raising the height of the entire bridge simply because that approach had fewer implications for wider engineering disciplines.

Outcome
It was decided that the new bridge at Irchester would be a composite structure with integrated steel beams and pre-cast concrete segments. All works eventually went ahead but only after a string of surveys and detailed planning, lasting months, had taken place, enabling the endangered creatures to be carefully moved.

In the final event – following the demolition and re-build of arch four at Irchester – the remaining four spans were upgraded courtesy of a concrete overslab which waterproofed the structure from above.