Beijing, China – Civil engineers at the North China University of Technology in Beijing have suggested that a PU–corrugated steel plate insulation lining could prevent railway tunnels being damaged by freezing conditions.
Guangyao Cui and Xuelai Wang explained that tunnel construction in cold regions is problematic, particularly in China where seasonal frozen soil accounts for more than half the land area, but many railway tunnels are being built in large numbers. Without adequate anti-freezing measures, the tunnels will gradually suffer damage, potentially affecting the railway’s safe operation.
Current freeze-proofing tactics rely on both active and passive thermal insulation measures, such as heating systems. These have already been used in some tunnels in northern China, but although this is relatively cheap at the outset, the ongoing costs mount up. Ground source heat pumps are also possible, but these are costly to install.
Passive methods include insulated doors and adding insulation layers inside the tunnels. The doors are impractical for high-speed trains, and there is a limit to how much anti-freezing effect can be achieved using insulation layers.
The Beijing team has developed an alternative lining solution. This comprises corrugated steel plates combined with a rigid polyurethane insulation layer, plus an additional waterproof layer to protect the PU layer. Using corrugated metal rather than flat sheets prevents buckling.
In a real-world test, the panels were applied to the inside of a 3.7km long, 10m high tunnel in northern China where there was already visible freezing damage. The panels were applied overnight, during the time when the train service was not in operation. The polyurethane layer was 5cm thick.
Field temperature tests were made, with the outdoor temperature between –18°C and –22°C. The temperature of the interface between the rock and the tunnel lining was above 0°C at all the points where it was measured, thus eliminating the freezing damage.
‘Compared to the conventional anti-freezing technology that destroys the tunnel concrete or drainage system, the installation of polyurethane-corrugated steel plate insulation lining is a permanent reinforcement of the tunnel without destroying the existing lining structure and drainage system conditions,’ they said. They also believe it could be used to treat damage such as cracking, back-voiding and frost-related water leaks in railway tunnels.
The work has been published in the journal Science Progress.
