The Blackheath Tunnel reopened on Monday (12 August) after a 10-week closure for essential repairs.
The 175-year-old tunnel underwent extensive masonry work to prevent water leaks that were damaging the railway.
The £10 million investment aims to improve travel for Southeastern customers by reducing delays and improving reliability.
With the tunnel now open, Southeastern has resumed its normal timetable, operating four trains per hour between Dartford and Cannon Street via Charlton, Blackheath and Lewisham.
During this phase of work, Network Rail and its partner Southern Integrated Delivery (SID) used a special industrial vacuum cleaner to clean the tunnel lining of years of soot build-up – a relic from the days when steam trains still ran through the tunnel.
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Over 10,000 bricks were used to repair the tunnel lining, repairing damage caused by years of freezing and thawing rainwater that had seeped into the ground.
In addition, detailed structural and soil investigations were carried out in preparation for further work planned for next year.
Although the tunnel remained safe, the leaks and moisture inside damaged the tracks and electrical equipment and led to delays and speed restrictions.
Last year, disruptions in the tunnel caused delays of around 1,000 minutes for Southeastern customers.
The Blackheath Railway Tunnel was opened on 30 July 1849 as part of the line between Blackheath and Charlton stations.
David Davidson, Network Rail’s Route Director for Kent, said: “We are grateful for everyone’s patience as we worked on the Blackheath Tunnel over the last ten weeks.
“We are in the process of renewing everything inside the tunnel, including replacing the tracks.
“This means we need to return to Blackheath to complete this work over the next few years so that we can maintain this Victorian building in the best possible condition.
“We will now assess what further repair work is required over the next year and will keep passengers and stakeholders updated on the next steps.”
Scott Brightwell, Southeastern’s Director of Operations and Safety, said: “The repairs being made to the tunnel will help provide a better journey for our customers and I would like to thank them for their patience during the summer closure.
“With the reopening of the tunnel we will be able to return to our normal timetable and during busier periods there will be four trains per hour between Dartford and Cannon Street via Charlton, Blackheath and Lewisham.
“Please check before travelling from Monday 12 August.”
