Tunnel lining work can be one of the most important aspects of maintenance and repair on a tunnel. This is particularly the case when the vulnerability of a tunnel to water ingress is increased by it lying below the level of a watercourse and still more if it passes beneath it.
London’s Tube network is one case in point, with the system passing under the Thames multiple times and also having to deal with other rivers, including the subterranean River Westbourne passing via a conduit above the platform at Sloane Square station. But the Underground is not the only system in Britain dating from the 19th century.
Glasgow’s Subway has seen some major refurbishment in recent years the first major project to do so since the 1970s. Improving the “structural integrity of the tunnel lining” was one of the key aims, with the intention being a reduction in water ingress, a vital issue given that the tunnels are all below the level of the Clyde and cross under the river twice.
This involved extensive grouting and improved management of the water that does get in, as well as a “better environment” to help spot future tunnel defects that may arise. Overall, this involved 14,600 m of tunnels being inspected and improved.
Unlike the Tube in London, which has been regularly expanded, the Subway has never been extended beyond its original 1896 circular route. This is something of a running joke in Glasgow, but it also means engineers are always dealing with tunnels excavated in Victorian times.
The earliest underground lines in London were in sub-surface tunnels built using the cut-and-cover method, unlike in Glasgow where they were excavated out of solid rock.
However, the oldest tunnel under the Thames, Brunel’s tunnel between Wapping and Rotherhithe, was completed in 1843. It was originally a pedestrian tunnel, although later the Tube adopted it as part of the East London line, now incorporated into the London Overground system.
The need to protect it against water ingress was a challenge from the outset, with flooding being a major problem during the 18-year project to construct it.