Mountfield Tunnel Slab Refurbishment

Rhomberg Sersa UK (RSUK) was awarded the southern slab refurbishment project by Network Rail in 2020. Mountfield Tunnel was one of three tunnels in the South East of England needing urgent works to maintain the safety and reliability of its rail infrastructure.

Network Rail contracted Rhomberg Sersa UK in 2020 to deliver GRIP 2-4 (Feasibility, Option Selection and Option Development) on life expired slab track in Mountfield Tunnel. They were mobilising to site after delays caused by the COVID pandemic, when the client informed that a section of concrete slab in the tunnel had failed. Failure of the concrete slab had caused a geometric twist fault, which led Network Rail to impose an Emergency Speed Restriction (ESR). They needed to remove the ESR as soon as possible to reduce impact on passenger services and asked if we could immediately mobilise to Mountfield and deliver emergency works: We stabilised the section of failed concrete slab by pumping high strength grout underneath it.

Following the emergency repairs, Rhomberg Sersa UK carried out the GRIP 2-4 works. Network Rail chose an IVES on roller compacted concrete pavement option to replace 30m of concrete slab at the tunnel portal. Two weeks before the works were due to begin, additional asset information revealed that the existing concrete slab was acting as a structural prop to the tunnel. Network Rail asked Rhomberg Sersa UK to create a new design and methodology that would avoid damage to the Tunnel. Their solution was an insitu cast slab, which Network Rail accepted and Rhomberg Sersa UK delivered during a nine-day blockade in October 2022.

The final stage of the Mountfield Tunnel Project was a collaborative effort between RSUK, Network Rail and supporting subcontractors to replace 500m of track and the remaining 250m of concrete slab. These works took place during a nine-day blockade from 7 April to handback on 16 April 2023.