01.07.14
‘Smart tunnel’ sensors monitor London’s ageing rail infrastructure
Source: Rail Technology Magazine June/July 2014
Mehdi Alhaddad, asset protection engineer at Crossrail and a PhD student at the Cambridge Centre for Smart Infrastructure and Construction, talks about the use of innovative sensors in monitoring London’s ageing rail infrastructure.
University of Cambridge engineers are using a range of innovative sensor technologies – in the world’s first ‘smart tunnel’ – to provide a detailed picture of how the UK’s ageing rail infrastructure is behaving, and how best to maintain and protect it for generations to come.
Located at the Royal Mail tunnel in central London, which was used to carry post across the capital from 1927 until 2003, an underground lab has been set up for researchers to measure, in real time, how the tunnel changes as one of the new Crossrail tunnels is constructed just beneath it.
Hundreds of low-cost sensors have been installed in a 30m stretch of the tunnel beneath Liverpool Street station, just a few metres above the excavation of one of Crossrail’s new stations.
Speaking to RTM, Mehdi Alhaddad, asset protection engineer at Crossrail and a PhD student at the Cambridge Centre for Smart Infrastructure and Construction (CSIC), said: “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 [100m].
“The project has been a unique opportunity for us to study the impact this is having on the infrastructure. In particular, there was always going to be some movement coming from the new excavation through to the existing tunnel. So we have been studying the behaviour of both tunnels in detail in relation to this – something which hasn’t been done before.
“We have also been able to install our technologies, and new ways of monitoring tunnels, in a real environment, which is extremely similar to the current stock of London Underground tunnels. So it was a perfect case study for our new technologies to show that they can work, which will add value to future design and mitigation measures.”
As part of the study, the CSIC team has used 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.
The technologies used include optical fibres which have been installed along the length of the tunnel – showing if the tunnel is deforming or bending. Wireless displacement transducers measuring displacement of one part of the tunnel relative to the next and wirelessly transmitting the data to a receiving station. Photogrammetry, or computer vision, techniques have also allowed the team to measure many more points than current methods and visualise what is happening in the tunnel.
In addition, long-lasting, ultra-low-power sensors, invented by PhD student Heba Bevan, have been installed throughout the tunnel. These sensors measure temperature, humidity, acceleration and tilt, and can be left in place for years without requiring the battery to be changed.
Mike Devriendt, associate director at global engineering consultancy firm Arup, who worked as a technical consultant on the project, added that until now, there hasn’t been a way to assess the impact of construction on cast iron tunnels with such pinpoint accuracy.
Alhaddad, who has been monitoring the tunnel since the technology was installed in February 2013, said: “The great finding so far is that our technology has worked and we demonstrated that it could be used in real cases. For example, we were able to measure the tunnels to see how they behave before they start to crack and start to become problematic.
“We were using our technologies to compete with the conventional monitoring methods and have matched whatever the original convention was.”
He also stated that the main brief and initiative for CISC in using the sensors was to help make the construction process of major infrastructure projects “cheaper and safer”.
The study, which will run on site for another six months before detailed analysis can carried out, has been a unique collaboration between academia and industry in assessing the way construction is currently carried out in the UK.
In addition to the work in the Royal Mail tunnel, the University has worked closely with Crossrail on ground monitoring on several of its construction sites. “Right across London, cutting edge technology is being used to ensure that tunnelling work being carried out for Crossrail doesn’t cause damage to structures above or below ground,” said Chris Dulake, Crossrail chief engineer. “The movement that we have seen from our bored tunnelling so far has been significantly less than we expected and we will keep on working hard to make sure that continues to be the case.”
Although detailed analysis of the CISC study is not available yet, it is hoped that by installing the kind of sensors that can give a continuous update about how much tunnels might be moving and what changes are taking place during excavations, important questions can be answered about the value of the industry’s current infrastructure, the future of it, whether it needs to be maintained, and whether it needs to be replaced.
Alhaddad said: “Currently, our construction industry seems to be falling behind in making as much use of the data and information that they collect on site and adding value to the construction sites they work on.
“Hopefully this research will work as a catalyst for change.”
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