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Confirmed: Bakerloo Line bulge caused by grouting

London Underground (LUL) has confirmed that a “bulge” that closed the Bakerloo Line last week was caused by grouting operations being carried out to stop water ingress into the Tube tunnel.

An LUL spokesman told NCE that grouting had taken place to seal up fissures that were causing “slight water ingress” into the running tunnel. The grout had “pushed out” the tunnel’s steel inner lining.

The bulge was formed in the crown of the southbound tunnel, to the south of Embankment station close to the River Thames. It was large enough to catch on the roof of two trains running on the line last Thursday morning, although neither derailed.

The Bakerloo Line has the smallest clearance of any of the Tube lines, with only around 150mm between the roof of the trains and the tunnel lining.

Local repairs were carried out to remove the bulge, and the line reopened later on Thursday evening.

The section of Bakerloo Line between Embankment and Waterloo stations runs beneath the River Thames. Construction dates back to 1900 and the line opened in 1906.

The tunnel was built through London clay and gravels, using a tunnel shield that was launched inside a caisson installed from a temporary pier built from the north bank of the river, close to Hungerford Bridge.

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