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Report | Liverpool flyovers' catalogue of faults

Above Liverpool’s busy city centre, the Churchill Way flyovers are eerily empty. The giant concrete structures once integral to the city’s road network have been slowly decaying for years. They are now closed, pending demolition.

Above Liverpool’s busy city centre, the Churchill Way  flyovers are eerily empty. The giant concrete structures, once integral to the city’s road network have been slowly decaying for years. They are now closed, pending demolition.

For decades the 239m-long north flyover has carried eastbound traffic away from Liverpool’s city centre, while the 285m-long south flyover has carried westbound traffic towards it. 

The pair of 1960s post-tensioned concrete viaducts was given a six month stay of execution last September. An inspection last summer led to the imposition of a 7.5t weight limit while Amey Consulting engineers conducted more detailed structural safety checks.

The news was bad. Engineers concluded that the flyovers are no longer safe enough to carry vehicles or pedestrians and should be demolished. Their report says that the cost of replacing them would be between £50M and £60M, while demolishing them without replacing them would only cost £5.7M. The city council chose the latter option on 22 February and demolition is set to start in the summer. The council has confirmed that it will not replace the structures and will instead divert traffic onto local roads. 

New Civil Engineer has had exclusive access to the site to see what led to the council’s decision.

The flyovers are already reaching what you would describe as potentially the end of their natural life, maybe within another 15 or 20 years

Amey had explored strengthening options such as plate bonding, external post-tensioning and adding additional deck supports. These were ultimately deemed unfeasible, particularly as there was concern about how much longer even the strengthened the flyovers could last.

“The flyovers are already reaching what you would describe as potentially the end of their natural life, maybe within another 15 or 20 years,” Liverpool City Council head of highways Andy Barr told New Civil Engineer

The flyovers were designed by WS Atkins and built by G Percy Trentham. Each structure comprises 10 spans with a continuous deck supporting a 7.3m wide carriageway with 800mm verges on either side. The ends of the flyover are supported on reinforced concrete abutments.

Both flyovers are supported on single 1.5m diameter concrete columns, which are cylindrical in plan and cast as an integral part of the deck. Both structures were constructed as a post-tensioned insitu concrete multiple box beams.   

The bases of the columns are supported on bearings below ground which allow longitudinal movement. The bearings consist of steel rollers sandwiched between steel plates with the whole assembly contained within a grease box for protection.

Amey’s most recent intrusive inspection of the viaducts in February found visible signs of structural distress in both including cracking above some supports. Measurements taken above several supports suggested the structure was overstressed and understrength.

The engineers discovered poor quality concrete and steel reinforcement placement and problems with the positioning of internal permanent formwork. 

Condemned Liverpool flyover

Condemned Liverpool flyover

An earlier inspection carried out by Amey last August uncovered a void around tendon ducts, where concrete had not been compacted adequately.

The inspection – concluded in August 2018 – involved intrusive investigations of post tensioning systems and tendons. Previous visual inspections – carried out annually – resulted in remedial work in 2005 and 2013.

Cracking and spalling of concrete at various locations in the deck soffit for the north flyover had also been picked up on at least three occasions since 2009.

In addition, Amey’s February inspection revealed that water had been leaking through the expansion joints at the east and west abutments of the north flyover and into the bearing shelves. 

Our primary areas of concern are the poor quality of original construction, subsequent deterioration and the current signs of structural distress

It also found water penetration in the deck interior, brickwork deterioration, failed movement joints and corroded abutment bearings.

“Our primary areas of concern are the poor quality of original construction, subsequent deterioration and the current signs of structural distress,” said Amey principal project manager Trevor Cherryholme when announcing the decision to demolish. 

He added: “More specifically, poor steel placement and spalled concrete, collapsed or failed formwork, failed drainage and signs of overstress in the deck are among our most significant findings. It is our view that there is no safe option other than demolition.”

It is also worth noting that no as-built drawings are available for the north flyover and so the bridge cannot be fully understood. The exact construction sequence used to build the structure is also unclear. Although the north flyover was originally designed to be constructed span by span; a technical paper published in The Structural Engineer in 1971 states that the contractor changed the construction sequence so that the final two spans of the northern flyover were constructed in one stage. This change in sequence resulted in an uneven distribution of dead loads and higher pre-stress losses, according to Amey.

Amey’s earlier structural assessment of the flyovers in August 2018. shows that the south flyover was only strong enough for a maximum live load of 7.5t with no more strength in reserve. Amey therefore advised an immediate loading restriction of 7.5t and for further investigations be undertaken to better determine the flyovers’ condition. Both flyovers were classified by Amey at the time as “immediate at risk” due to the extent of structural distress and lack of strength observed during the investigation works.

In January a Liverpool City Council source also told New Civil Engineer that the fabric of the structures had been “crumbling in several places” due to wear and tear, stress fractures and because material was being dislodged by water. Cracks in the structure had also widened due to frost, the source claimed.

Another source close to the February investigation told New Civil Engineer of a near miss when a fragment from one of the parapets fell onto the car park below. 

Demolishing the structures will bring its own obstacles. A footbridge link to the Liverpool John Moores University campus passes underneath the flyovers. Amey has said it is economically unviable to retain most of them, except for one span which will require access ramps or steps to be built.

Junctions near the viaducts will also have to be reconfigured to allow for the increased traffic flow resulting from the viaduct demolition, according to Amey. Traffic surveys and assessments are ongoing to help engineers determine the new junction designs. 

The council is also now spending £10M on proposals to improve nearby infrastructure to cope with the increased traffic flow caused by the demolition of the viaducts.

The Churchill Way flyovers are a relic of a plan from half a century ago that was never completed

Consultants and specialist contractors are now developing a detailed demolition proposal, to be checked by structural engineers. A safety watching brief is now in place until demolition takes place. This will include inspections from ground level and at touching distance, the removal of loose concrete, and the maintenance of debris netting to protect people and property from falling concrete.

 “The Churchill Way flyovers are a relic of a plan from half a century ago that was never completed,” Liverpool City Council cabinet member for highways James Noakes admits. “Public safety is absolutely paramount, and despite the obvious inconvenience the demolition will cause, we cannot compromise on safety and it is simply not economically viable to make them safe.”

 

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