Together, the sensors paint an incredibly accurate and detailed picture of how the older tunnel is behaving, which will inform the best way to protect and maintain it.
Mehdi Alhaddad
Twenty-five metres beneath central London is the world’s first ‘smart tunnel’, where ground-breaking new sensing technologies are providing massive amounts of information about the UK’s ageing infrastructure, and how best to maintain and protect it for generations to come.
The Royal Mail tunnel, which was used to carry post across London from 1927 until 2003, is now the site of a unique underground laboratory where University of Cambridge engineers are monitoring movement in real time and seeing how the tunnel changes as a gigantic new tunnel is constructed just beneath it.
Hundreds of low-cost sensors have been installed in a 30 metre stretch of the Royal Mail tunnel beneath Liverpool Street Station, where it is located only a few metres above the excavation of one of Crossrail’s new stations. Crossrail, a new commuter rail line across London due to open in 2018, is the largest civil engineering project currently under construction in Europe, and has put technology at the heart of its efforts to ensure minimal impact from its construction on adjacent infrastructure.
The Royal Mail tunnel is just over 2.5 metres in diameter. By comparison, the Crossrail platform tunnel being excavated close beneath it is nearly 11 metres in diameter – more than the height of two double-decker buses.
“A project as big as Crossrail comes with all sorts of engineering challenges,” said Professor Robert Mair, Head of Civil Engineering and of the Centre for Smart Infrastructure and Construction (CSIC) at the University of Cambridge. “One of the most important of those challenges is how you excavate large tunnels underneath urban infrastructure without causing any distress to buildings or other tunnels.”
The two tunnels run parallel to each other for more than 100 metres, with just a few metres between them. This is the first time that two tunnels have been dug in London in such close proximity and parallel to each other for such a long distance.
Some limited movement of the Royal Mail tunnel, in the region of only a few millimetres, is inevitable during the Crossrail excavation, but the questions that the Cambridge technology is answering is how much movement is happening, what form the movement is taking, and whether it is within acceptable limits – the mechanics of which are quite complex.
The CSIC team are using four different low-cost sensing technologies, which together can detect movements as small as one-hundredth of a millimetre, enabling any potential problems to be spotted and corrected well before they represent any risk to the older tunnel. To date, the minor movement that has taken place is well within the acceptable limits.
“Together, the sensors paint an incredibly accurate and detailed picture of how the older tunnel is behaving, which will inform the best way to protect and maintain it,” said PhD student Mehdi Alhaddad, who has been monitoring the Royal Mail tunnel for more than a year. “In future, this type of technology could also be used to efficiently and economically monitor much of the UK’s Victorian and 20th century infrastructure, such as the miles of tunnels of the London Underground, 70 per cent of which is made of cast iron, similar to the Royal Mail tunnel.”