After five days of work between Axminster and Pinhoe, Network Rail thanked passengers for their patience as engineers worked at the Honiton Tunnel to protect the site from landslides.
Due to the area around the tunnel, the section of line has suffered from landslides in the past, including one in 2001 which derailed a train.
Engineers have completed work on two retaining walls to stop any landslides where the line crosses a trench leading to the tunnel.
The drainage systems at the cut have also been improved which, together with the new retaining walls, will make the line more resistant to heavy rains in the future.
Follow-up work is expected to be completed in December, with another line closure next year.
Mark Killick, Network Rail’s Wessex Route Manager, said: “We would like to thank customers for their patience during the disruption last week. We have made good progress which will provide our customers with a much more reliable railroad in the future.
“This is just the start of a long-term program to make this rail cut more resilient. There will be weekend closures as we continue our work, but this five-day closure means we won’t we won’t need that many.
“It was a difficult five days as our teams found a number of natural springs which made it difficult to dig the earth and pour the concrete, but they adapted the work program to ensure that a lot of progress was still made.”
Christian Neill, Director of Customer Experience for South Western Railway, said: “I am delighted that Network Rail has made fantastic progress and that the line between Axminster and Pinhoe is reopening on time.
“I would like to thank customers for their understanding as this vital work is carried out, particularly in the context of wider challenges on the West of England line.
“These upgrades will strengthen the reliability and resilience of a vital part of our network, and the progress of the past week will avoid the need for as many future shutdowns as the renewal project continues.”