In the second half of the 19th and early 20th centuries, hundreds of railway tunnels were built in Europe. They are largely still in operation today. In the coming decades, a considerable number of tunnels are due for substantial renewal. With the Tunnel Enlargement System (TES), Herrenknecht has developed a solution for enlarging the tunnel profile of old railway tunnels while rail traffic continues to run.

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https://tunnelcontact.com/discussion/view/59218/herrenknecht-develops-tunnel-enlargement-system-for-enlarging-tunnels-even-when-they-are-in-use