River Eden Viaduct, Carlisle

Product: Underwater concrete
Volume supplied: 682m³
Client: Network Rail 
Contractor: Story Contracting

Overview 
Heidelberg Materials designed and supplied specialist underwater concrete to stabilise the foundations of two viaducts over the River Eden in Carlisle, Cumbria. The repairs have been made to the structures as part of a £1.3 million Great North Rail Project investment.

Project description
The 70-metre long rail viaduct on the West Coast mainline in Carlisle consists of five stone piers and a concrete deck. During maintenance on the structure, an underwater survey confirmed that fast-flowing water caused parts of the riverbed to wash away, risking the viaducts’ foundations, exposing the piers and undermining the structural integrity of the viaduct. 

Heidelberg Materials, working for client Network Rail through engineering specialists WSP, design and supplied specialist underwater concrete to stabilise the foundations and protect the West Coast mainline rail link. 

Detailed laser surveys highlighted the deterioration of the riverbed, which led to trains running at a reduced speed over the Victorian and adjacent 1940s-built viaducts to ensure safety. In order to ensure a stable platform for the viaducts’ columns and piers, Heidelberg Materials designed a bespoke underwater concrete solution incorporating admixtures from Sika. 

Research and development work was carried out in Heidelberg Materials’ nearby Carlisle laboratory to ensure the scheme was undertaken on schedule. Terry Balmer, technical manager at Heidelberg Materials, said: “We engaged with the Network Rail engineering team to develop a bespoke solution to overcome complex placing difficulties and strict environmental controls. In less than 40 hours, the technical team had designed and tested an anti-washout, self-compacting concrete ready for the remedial works. The success of the material relied on concrete admixture technology to overcome the challenging engineering requirements.”

To stabilise the foundations, a total 400m³ of concrete was pumped over 100 metres and placed by specialist diving teams to stabilise the bridge foundations. The underwater visibility was poor with significant work needing to be done by touch. To complete this safely, the river was temporarily
diverted and calmed used 2,200 tonnes of rock. This aided the divers and helped reduce any washout into the river as the concrete was pumped into position. 

An additional 282m³ of specialist underwater concrete was added to the 64 tonnes of permanent interlocking sheet piles to repair the stone piers. The bespoke concrete mix developed by Heidelberg Materials, which contained a propriety anti wash out admixture system supplied by admixture partner Sika, was poured between the pier and the sheet piles, with a capping beam formed at cut-off level. Early engagement between Heidelberg Materials
and Story Contracting enabled a design solution to be formulated that considered both the practicalities of construction and environmental considerations. The admixture system was tailored to speed up placement of the concrete and prevent any harmful “wash out” of the cementitious material into the River Eden. 

Access was a significant challenge for the project and a temporary causeway was constructed in order to gain sufficient access across the river. The works were planned and implemented in controlled phases to maintain river flow and allow fish to migrate unhindered. 

The renovation work was put to the test soon after completion when the River Eden encountered severe flooding in December 2015. Structural inspections in early 2016 showed no damage to the strengthening work, highlighting the success of the solution. 

Craig Jackson, works delivery manager at Network Rail, added: “These vital repairs have helped to make the viaducts safe to keep passenger and freight train moving on the West Coast mainline.”