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STRUCTURES

Bristol flyover repairs to cost £200M

Costs increase tenfold after detailed structural inspection
By Belinda Smart

National Highways has increased the estimated cost of repairing a Bristol motorway overbridge, after a detailed inspection of the structure.

Initial estimates put the cost of refurbishing the Eastville Viaduct at £26M, but the structural investigation revealed “significant defects”, putting the likely revised budget at £200M.

The 1.1km concrete road bridge, built in the 1970s, carries traffic over Junction 2 of the M32 motorway and connects central Bristol to the M4.

A 521-page report by National Highways inspectors lists issues including poor installation of bearings and a “lack of quality control” during concrete pours.

The bridge’s concrete road surface is also deteriorating and bearings are corroding. On the underside of the bridge, concrete is cracking, exposing reinforced steel. Areas of spalling measure 3m wide, and corroding steel reinforcement is visible in places.

Sawdust and off-cuts of reinforcement nails and screws were also found in the bridge’s structure. The report said this “clearly demonstrates a lack of any quality control when preparing the formwork for concrete pours”.

NCE has seen a report which lists issues including:

• Blocked middle and south drainage system catchment trays and associated carrier pipes for the comb and tooth joints
• Central and southern scissor joint drainage catchment troughs are subject to significant corrosion and water staining/ leakage. Mounting brackets are corroded.
• Blocked north abutment drainage system. The bearing shelf is full of detritus blocking the carrier pipe from the bearing shelf and into the main chamber. The chamber is overflowing down the revetment to the footway and pavement
• Several areas of spalling in the deck soffit, around drainage weep holes ranging from approximately 500mm by 500mm to 3.5m by 2m.

The report also recommends that work scheduled to be carried out in National Highways’ five-year RIS2 spending programme should include repairs to the concrete deck. It says void formers made from expanded polystyrene foam “have risen to the surface of the deck during the concrete pour, reducing the thickness of the deck”.

These are used to reduce the volume and weight of large concrete structures.

It further notes: “Based on the current condition of the surfacing and its maintenance history, replacement of the waterproofing and surfacing is required along with extensive concrete repairs to the deck.”

The report also recommends bearings be replaced or refurbished. Many of the bearings are showing signs of corrosion with those featuring centre guides to limit their movement appearing to be the worst affected. Some bearing plates are damaged at the transit bolt positions with some holding down bolts incorrectly tightened.

National Highways route manager Sean Walsh confirmed that along with the repairs, the original scope of work had expanded. “This will include concrete repairs to the bridge itself, new barriers that will also incorporate noise mitigation, new gantries, drainage, lighting and new waterproofing, as well as a new contiguous deck to allow traffic to be moved around during construction.

“We also believe this will be more than the £22.6M [initially] reported.”

He continued: “The early estimate in the structure’s general inspections report was based on individual and visible repairs at that time and not the full extent of the scheme we now plan to deliver, which includes additional work to extend the life of the whole structure and replacement of such assets as gantries, technology, drainage and noise and safety barriers.

“It also didn’t include other expenses such as providing a complex traffic management solution to maintain as much traffic capacity as possible.”

A National Highways spokesperson told NCE: “Our working assumption is currently over £200M, but this will be guided by detailed design and mitigation.”

Work on the bridge, which National Highways says remains “structurally sound”, will not start until 2026. The spokesperson told NCE the 2026 start date was necessary “due to scheme development, detailed design, adequate communication and development of scheme mitigation. It’s a very complex scheme so we are making sure we have everything in place.”