Excavation and tunneling projects are nuanced and complex. The amount of planning and technical execution that goes into ensuring the job is completed successfully is significant.
Nowhere are these projects more challenging though then when they take place in urban settings.
When these major excavation and tunneling projects take place in urban environments, it is not only a priority to create the tunnel, but also to excavate in a way that does not cause distress or deformation to the surrounding infrastructure.
University of Cambridge engineers are taking advantage of a unique opportunity in London to answer a lot of questions about how large-scale excavation impacts cast iron tunnels.
The project underway is a Crossrail platform tunnel that is almost 11 meters in diameter.
The new tunnel runs parallel to an old cast iron tunnel, the Royal Mail tunnel, which was employed to transport mail from 1927 until 2003, for a long stretch.
Research engineers are taking this opportunity to use sensor technology that has been widely in the lab to monitor how excavation on the new tunnel is impacting the existing infrastructure.
To receive accurate and detailed information, hundreds of low-cost sensors were installed in the Royal Mail tunnel. There are several different types of sensors that are located throughout the tunnel.
Optical fiber sensors are used to monitor the strain longitudinally all the way along the Royal Mail tunnel to capture how the tunnel deforms and bends.
Wireless displacement transducers were placed along the railway to measure displacement from one part of the tunnel in relation to other parts of the tunnel. As it receives information, it is able to send and that on wirelessly to a receiving station.
The sensors provide incredibly accurate information and are claimed to be able to detect displacement as minimal as one-hundredth of a millimeter.
Other sensors provide information on temperature, humidity, and acceleration to understand what conditions are like inside the tunnel.
Advanced computer vision techniques are also being implemented to monitor the project.
Collectively, the sensors are providing an extremely accurate portrayal of how the Royal Mail tunnel is responding to the construction work going on around it. With this wealth of instantaneous information, the Crossrail engineers are able to diagnose potential issues and make the necessary adjustments to protect the historic piece of architecture before any serious damage occurs.
The value these types of sensors provide will not only be beneficial to this project, but could also prove to be very useful to other projects in urban areas moving forward across the globe.
The ability to pinpoint how the construction affects cast iron structures will be especially beneficial to any future projects that take place in the London Underground. 70% of the London Underground consists of cast iron.
This inaugural “smart” tunnel has already returned exciting results for the Cambridge team. It will be interesting to see where this cutting edge technology goes from here in the future of excavation projects.