Harrison Road Closure Update

Summary

The map below shows the two bridges that have been affected and caused closure of most of Harrison Road. 

Rail Bridge

Bridge over disused railway line – now public Cycle/footbath/greenspace. 

Closed since earlier this year.

As part of routine structural inspections, a detailed assessment of the bridge was carried out, which determined that it failed to meet the required load capacity for normal traffic. In response, the council had been prepared a Traffic Regulation Order (TRO) to introduce weight restriction. However, due to the critical nature of the structure—specifically its reliance on cast iron beams, which are inherently brittle and have no ductility—engineers also undertook further testing to assess any underlying defects.

Magnetic Particle Inspection (MPI) was carried out on the main internal cast iron beams to verify their condition. The results, have unfortunately confirmed the presence of three cracks, with the largest measuring approximately 2 metres in length. Given the nature of cast iron, which is highly susceptible to sudden failure and extremely difficult to repair, the risk posed by these defects is too significant to allow continued vehicular use of the bridge. As a result, engineers had no safe alternative but to close the road with immediate effect.

The internal cast iron beams were found to be cracked and need to be removed. It was Proposed that the underside of the bridge will be flat concrete rather than the series of small arches. 

The cast iron parapets and edge beam are going to be incorporated into the new design, so the bridge will look the same road level and on the approaches on the cycle path. Minor alterations will be required to the parapet, but these will be on the internal faces and buried within the carriageway.

Canal Bridge

Canal Bridge is also closed. It was initially closed due to the concern that the same defects may be present, but the engineers have fortunately verified that there are no issues with the (similar) cast iron beams on this structure. However an assessment of the load carrying capacity conducted around the same time recommended a weight limit on the bridge. In the next couple of weeks they will be carrying out some trial pits to verify the structure under the road, to inform if this weight limit is required, and if so, what the limit needs to be.

Next Steps

The works will involve the demolition of the remaining existing bridge structure and installation of a falsework support system to facilitate construction of the new deck. Due to the nature of these activities and associated health and safety risks, the bridge will need to have a full closure above, and below during this period. 

This will be reviewed throughout the project and access will be re-opened when feasible. Signed diversion routes will be in place.

The works is likely to take another 4-5 months. 

Engineers were working towards a demolition date of 11th August – but this has been delayed.  Before demolition can happen, engineers want to have a permanent design solution in place and a good idea of lead-in times for key materials such as new bridge beams. The design is proving difficult due to the extensive (around 15) public utility ducts which currently cross the structure and need to be incorporated back into the new deck. And engineers want to minimise the duration of the footpath closure as much as possible. There is a chance demolition works will be delayed as a result.

So whilst the council are working through those, they have opted to keep the existing footpath over, and cycle path below, open.

The engineers wish to minimise the closures as much as possible, so will work on a ‘just in time’ basis, whereby the closure timescales will work backwards from the date they are required for the next stage of the project, rather than being done ahead of time and causing unnecessary disruption in the meantime. 

Focus is still on the Road Bridge, but the trial pits required to verify the Canal Bridge assessment will done in the next 2-3 weeks.