The 175-year-old Blackheath tunnel has reopened after a 10-week closure for repairs.

Trains between Blackheath and Charlton stations are now operating once again following strengthening and waterproofing work on the Victorian structure.

Southeastern Railway has completed the programme of essential repairs that will help to improve reliability and safety for passengers. At its peak, the project’s workforce was more than 100 people working day and night

Services have returned to the normal timetable along the Woolwich and Bexleyheath routes following the re-opening. There will be two trains per hour to Cannon Street via Charlton and Blackheath stations, which previously ran via Greenwich when the tunnel was closed.

The specialist repair work is believed to be the first of its kind in the UK. Engineers injected expansive grout into the pockets of sand and gravel surrounding the tunnel to strengthen the ground. This innovative technique knits and compresses 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.

David Davidson, chief operating officer for the Southeastern Railway, said: “Over the last 10-weeks we’ve completed a groundbreaking programme in the tunnel that will 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.

“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’.

“I want to thank our customers for bearing with us while the tunnel was closed for this work to deliver better journeys.”

The project has included:

• 1,000 core holes drilled, stretching 900 metres – three times the height of The Shard or the length of Greenwich Park
• 4,000 injection tubes installed, totalling 13 kilometres – enough to reach from Blackheath tunnel to London Zoo
• 55 tonnes of grout used – equivalent to the volume of two swimming pools
• Tunnel monitoring system detects movement to 0.01 millimetres – less than the thickness of a human hair