Soil squeaks give early warning of infrastructure collapse

The concrete and the clay beneath my feet begin to crumble, as the popular 1960s song goes. It’s a case of truth in art. Structures sitting on or in earth – which represent most of the built environment – can seem perfectly stable for decades, and then collapse without warning.

Such disasters have been seen recently in the UK, with the collapse of the Whaley Bridge dam in Derbyshire and in Brazil, where a mining dam suddenly collapsed in February causing over 200 deaths.

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Further reading

• Chinook helicopter joins Whaley Bridge dam operation 
• Modelling technique assesses the impact of dam collapse
• Last week’s poll: UK infrastructure and extreme weather

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One reason for such collapses is that earth is a complex and unpredictable material. It is composed of particles of widely varying sizes and shapes, and changing conditions, such as variable loading and moisture, can cause a previously stable area to start deforming.

Once this process begins, it is very difficult to predict how the constituent particles of the earth will interact with each other, and whether structures supported by this region will remain stable.

As such variables are often connected with population growth (i.e. increasing traffic on roads and alterations in train timetables) and with climate change (changes in local rainfall or aridity) these problems are becoming more pressing; a situation which civil engineers believe is likely to continue.

Alister Smith of Loughborough University’s School of Architecture, Building and Civil Engineering has been studying this phenomenon for some years and this week was awarded a Philip Leverhulme Prize of £110,000 to develop a monitoring system based on his research.

The Leverhulme Prizes are awarded by the eponymous trust to industrial researchers whose work has already attracted international attention and whose future careers are judged to be exceptionally promising.

Smith is the principal investigator on an EPSRC-funded project called Listening to Infrastructure (LTI). The project notes the rapid deterioration of many vital parts of existing infrastructure, and is focusing on acoustic methods to monitor the ground movements that might cause such deterioration.

When any material deforms, the movement of its constituent particles (or crystals in the case of metals) against each other generates high-frequency sound. Known as acoustic emissions (AE), such sounds are commonly used to monitor the condition of materials such as concrete and steel.

However, because earth deforms in an unpredictable way, unlike the well-understood cracking mechanisms of construction materials, it has been very difficult to interpret the AE signals generated by ground movements. Smith and his colleagues have published their research in the Journal of Geotechnical and Geo-Environmental Engineering, Geotechnique and elsewhere.

Smith’s LTI project applies artificial intelligence to interpreting the ultrasonic AE signals of deforming earth that is supporting infrastructure. He is determining whether AI-equipped acoustic sensors can be used to automatically extract knowledge of the health of deteriorating buried infrastructure systems from the raw AE data they extract, and whether this technology could be used to develop a continuous AE-monitoring system that could be distributed at separate locations along the length of such infrastructure.

“If we can listen to geotechnical assets with intelligent sensors – analogous to a stethoscope being used to listen to a patient’s heartbeat – we will be able to provide information on the condition of infrastructure and early warning of deterioration in real-time”, explained Smith. “Our vision is of a family of AE sensors distributed globally, protecting people and infrastructure worldwide by providing an early warning that will enable interventions to be put in place.

“These interventions could be an emergency evacuation or preventing traffic from accessing part of the network (actions which protect people), or they could be in the form of maintenance and remediation, which prevents catastrophic failures and extends an asset’s lifespan. This research has the potential to revolutionise infrastructure stewardship and it is an honour to have my past research achievements and ideas for the future recognised by receiving this Prize.”