Tunnelling has always been a high-risk activity, their design and construction deal with challenges and problems that do not exist as part of other disciplines of construction. Tunnels must navigate the ground that surrounds them – the materials you deal with are ‘out of sight’ and what gets built is rarely seen by the public. As such, when failures occur, they are often packaged away as errors of risk management etc., or mistakes in project leadership.
But how can it be that highly skilled geotechnical engineers keep getting it wrong?
The 2009 Cologne Metro failure claimed 2 lives. The same year there were tunnel collapses in Albania, Prague, and on the Cairo Metro, and in 2012 five workers were killed after a subsea tunnel collapsed during construction in Japan - but this is just the tip of the iceberg. In the UK, we had the infamous Heathrow Express T4 collapse in 1994, that coincided with major metro tunnel collapses in Munich, Taipei and Los Angeles. Then the infamous Humber tunnel collapse in 1999; the Stoke Lane train derailment in 2013, and even as recently as last year there was a collapse above the Chiltern Tunnel route on HS2 that is currently under investigation.
So, what is going on? Why do tunnels collapse in the first place?
