A 175-year-old rail tunnel in south-east London has reopened after a 10-week programme of repairs.
Network Rail said Blackheath Tunnel, which runs between Charlton and Blackheath, had undergone “a pioneering strengthening and waterproofing process”, believed to be the first of its kind in the UK and potentially the world.
Engineers injected expansive grout into the pockets of sand and gravel surrounding the tunnel to strengthen the ground – knitting and compressing the loose material tightly together.
A further layer of grout was applied to the back of the tunnel lining to waterproof the worst-affected areas, helping to preserve the brickwork and track, signalling, and other railway equipment in the tunnel for years to come.
The techniques trialled and used successfully in the Blackheath tunnel during this closure will now be replicated across other parts of the rail network.
South Eastern Railway chief operating officer David Davidson said the work would improve reliability by strengthening and waterproofing the structure to better protect the railway.
“Savings from this approach are estimated to be around £10m and this can be reinvested across the network to deliver more improvements that will keep passengers moving,” he said.
“Last summer our engineers cleaned soot from the tunnel lining, carried out detailed surveys and replaced thousands of bricks to stop water getting in. This year we’ve installed a new tunnel lining, rebuilt drainage systems and completed essential track work, including the removal of the waterlogged sections known as ‘wet beds’.”
During the works, engineers drilled 1,000 core holes, installed 4,000 injection tubes, totalling 13km, and used 55 tonnes of grout.
