Unseen work continues as M5 Avonmouth Bridge marks 50th anniversary

Over the past five decades a significant amount of unseen work has gone into maintaining the bridge and currently a programme of welding is being undertaken on the underside of the structure by the company responsible for England’s motorways and major A roads.

The original six-lane bridge was designed by Freeman Fox & Partners, and starting construction in 1969, principal contractors took five years to build and install the bridge over the River Avon near Bristol.

Completion was delayed by two years following construction issues with similar box girder structures in Melbourne, Koblenz and Milford Haven, and after further strengthening work, the bridge eventually opened for traffic on 24 May 1974.

Fifty years on, and the bridge – along with the nearby, year older Wynhol Viaduct – remains one of our iconic structures and a gateway to the South West, carrying an average 125,000 vehicles per day.

Strengthened and widened to eight lanes between 1996 and 2001, the structure:

• is 0.9 of a mile in total length
• is 40 metres wide
• has a ground clearance of 30.5 metres
• is made of reinforced concrete and steel
• is surfaced with a denser, durable and flexible surface material (Gussasphalt)
• features a cycle/footpath alongside the southbound carriageway

Funding and maintenance of the arterial structure has been the responsibility of central government, National Highways and our predecessors for all of its 50 years of service, latterly in partnership with Amey.

Large water crossings such as Avonmouth, the M4 Prince of Wales Bridge and M48 Severn Bridge require specific maintenance and inspection regimes, and all three structures are now looked after by our dedicated Specialist Bridges Inspection and Maintenance (SBIM) team.

As part of a robust inspection and maintenance regime, our teams have been carrying out extensive welding within the structure since October and a further £160,000 of welding work is due to start shortly.

Like the welding, most of the maintenance and renewal work goes unseen by the travelling public, taking place underneath the bridge, along the parapets and within the chambers and mezzanine flooring of the structure.

Abseiling engineers and cradle platforms have been employed as part of inspection and maintenance work, scaffold bridges are also being installed to enable safer repair work and easier access to the structure, while at the visible road level the bridge expansion joints are routinely inspected, assessed and repaired.

Terry Robinson, our South West Engineering Team Leader, said:

“We have a robust inspection regime and examine all our bridges and other structures in line with the published guidance in the Design Manual for Roads and Bridges.

“This includes general visual inspection every two years and more detailed principal inspection every six years, which identifies and records defects in reinforced concrete, steelwork and other construction materials, although structures such as the Avonmouth Bridge have more bespoke regimes, requiring a dedicated team to look after them.

“Through a programme of structural inspections, investigations and assessments we ensure that substandard and potentially vulnerable structures are identified, safeguarding measures adopted, and like the Avonmouth Bridge and Wynhol Viaduct, fully maintained for many years to come.”

Paula Hewitt, Chair of the South West Infrastructure Partnership, which includes infrastructure sector experts across the region, said:

“The Avonmouth Bridge is not only an iconic piece of infrastructure but is so important for connectivity in the South West.

“Looking after our critical infrastructure to ensure it can meet the future needs of the region is essential and it is great to see National Highways investing in the bridge’s maintenance to ensure it is able to meet our future needs.”

Safer and modern methods of work are continually explored, and along with gantry and runway beam studies, we've trialled the use of a concrete climbing robot to potentially lessen the need for rope access.

Shane Stephens, Senior Inspection Assurance Manager for our SBIM team, said:

“Like all the infrastructure across the Strategic Road Network, the Avonmouth bridge requires plenty of TLC, and one of the main challenges is to ensure safe access for the inspection and maintenance work around this large and significant structure.

“The Avonmouth Bridge, like the M4 Prince of Wales Bridge and the M48 Severn Bridge, is a real feat of engineering, and as current custodians, we take a lot of pride in our work as we move into the next 50 years of its life.”

Get more details on our work in the South West.