Fragile Construction Environments
There are three main construction methods used to build a tunnel: a cut-and-cover tunnel, a bored tunnel and an immersed tube tunnel. Each method of construction faces its own difficulties and potential risk.
Due to the natural surroundings, it can often be difficult to foresee potential risks prior to project implementation as it is significantly influenced by nature. A huge number of the risks involved in tunnelling revolve around collapse, which is largely due to ground movement, such as water/mud/runny sand breakthroughs, excessive growth of convergences and damage due to pressure building, just to name a few.
Proactive measures need to be implemented to minimise any major damage. Data on the costs involved in tunnel collapses or mitigating any ramifications from movements are unavoidable and can in some circumstances lead to millions spent. One prime example of this is the tunnel collapse during construction of the Heathrow express back in 1994, which lead to an extensive £150 million cost of repairing the collapsed tunnel.
Current methods for tracking ground movement before, during and after construction however are labour-intensive and expensive – it’s very much still a manual process, with checks of the track and surrounding land taking place on a monthly or quarterly basis depending on the risk level. The manual processes leave many gaps for error and the constant need for boots on the ground to complete this process quickly racks up costs.
Evolving risk management with InSAR
Interferometric Synthetic Aperture Radar (InSAR) can detect and measure displacement of the ground over time and is based on the comparison of multiple images taken by satellite-borne radar instruments. Unlike manual investigations, the ground movement history and current status could be assessed prior to the project starting.
InSAR has a high precision rate with the ability to detect as little as 1-2mm of displacement per year. InSAR technology gives the ability to continuously monitor ground movement around tunnelling sites, making it easier to foresee any possible damage and safety issues to rail infrastructure and ensure movement can be responded to with necessary adjustments. This method means more of the monitoring process can be achieved remotely, as it reduces the need for people on the ground conducting manual tests, reducing costs for the overall project.
SatSense’s solution continually processes data for the whole of the UK with new measurements available every few days. The archive of data acquired by satellites also means we are able to provide historic ground movement data, dating back almost seven years, which complements existing technologies while being integral to planning applications and asset monitoring reports.
InSAR enables firms to take a more proactive approach to their risk management, to be more aware of problems early on, have a complete bird's eye view of the entire project and focus resources on the required areas.
We are currently working with Network Rail to help better understand how InSAR can identify movements around existing tunnels across areas of the UK rail network. Interested in finding out more about how SatSense’s InSAR data could aid your future projects? You can visit our website or get in touch for more information.