Eyes for sore sites: a life of geophysics

When he started work as a 16-year-old apprentice electrician on Merseyside, Nigel Cassidy could never have imagined that one day he would be a Professor of Geotechnical Infrastructure Engineering, analysing the behaviour of sniffer dogs to improve algorithms for robots and giving expert advice on the ‘weird’ soils of Widnes.

Yet today, 30 years later, he is a world-leading geophysicist focusing on the development of remote monitoring, modelling and inversion techniques to solve practical environmental and geoengineering problems. His extensive research spans monitoring tree-induced subsidence through to the numerical modelling of high-frequency electromagnetics.

Nigel’s research interests have changed and evolved over the decades: now they lean very much towards the interpretation of data that geophysical tools and techniques – from reflection seismology to gravimetry – unearth about the ground beneath our feet. Moreover, he believes the key to solving problems ranging from land contamination to large-scale infrastructure projects is to further our understanding of how to predict the behaviour of materials. Only by deepening our insight into the natural world can we develop effective manmade ways to combat obstacles – both now and in the future.

For Nigel, those materials tend to be unusual and unpredictable, such as a waste product known locally on Merseyside as the ‘galligu’. The properties and effects of this substance were explained to the audience at his recent Inaugural Lecture, which was entitled ‘Eyes for Sore Sites: a life of Geophysics’.

The address was part of a series of Inaugural Lectures run by the College of Engineering and Physical Sciences to showcase its leading scientists who are pushing the boundaries in their disciplines. These events, which are open to the public and free of charge, mark an academic’s promotion to Professor, but also provide a rare opportunity to hear first-hand about their life and research.

Taking the audience through the story of his career to date, Nigel – who is Head of Civil Engineering – explained that millions of tonnes of galligu, a waste product from the soda ash and soap manufacturing industry of the late 1900s, had been dumped across swathes of land around sites in Widnes, Runcorn and St Helens.

Because of its unique properties – when it is in an oxidised, dry state at the surface it has a ‘stiff’, silty-sand texture, but when wet and buried it softens and becomes thixotropic (solid and stiff under static conditions, but viscous and deformable over time when agitated or otherwise stressed) – in the early 2000s it was still causing serious ground stability problems in the Widnes area. As a result, much of the land affected had been left undeveloped.

‘A bit like tomato ketchup, in some forms the galligu flows; in others it’s elastic – depending on its chemical state,’ explains Nigel. ‘This means that over time, the ground moves, especially when loads are placed on it.

‘I started working on this problem soon after completing my PhD in Ground Penetrating Radar Modelling, as part of the Widnes waterfront redevelopment programme, and I found a way of working out how deep the galligu was and how to differentiate its properties – in other words, how gooey it was. This enabled me to characterise and then predict changes in the ground surface. It’s the unpredictable nature of materials such as this that interests me. Dealing with galligu is still relevant now because there is lots of it around area of the newly opened Mersey Gateway Bridge.’

With more than 100 research articles in near-surface geophysics and geo-environmental engineering to his name, Nigel came to academia relatively late in life.

‘As a boy I was always interested in engineering and the natural world, but I left school at 16 and became an electrician, working in the industrial sector for about ten years. Then I went into academia. I was 31 when I finished my first degree, in Geology and Geophysics, at Liverpool before going on to Keele for my PhD, where I stayed as a Lecturer and later a Reader until I left to come to Birmingham as a Professor in 2016.’

As well as using geophysical tools – the ‘eyes’ of his lecture title – to help see beneath the sub-surface to solve ‘sore’ contaminated land problems, another area of Nigel’s research is the development of robots and AI machines to help overcome environmental and geo-engineering obstacles.

‘One thing that really interests me is the way we use the information that our tools provide us with,’ he says. ‘As I tried to get over in my talk, we can use our tools and machines to look into the sub-surface, but it’s the interpretation of the data that is crucial. If you put rubbish into any machine, be it a computer or an autonomous robot, you will get rubbish out.

This interest was sparked when Nigel started using geophysics to look for clandestine buried objects – from bodies to landmines. ‘I ended up working with dog trainers and that led me to look into the way we use geophysics for conducting searches – looking at patterns of behaviour to help refine investigations by using geophysics in a more focused way. That led us on to new ways of to search below the ground.’

What fascinated Nigel about sniffer dogs was how they searched. A dog is an organic, autonomous robot, trained and programmed to use its sensor – its nose – to search for buried items. ‘What a dog does naturally is what we’re trying to do now with robots. So, we were using patterns of dog search techniques to try to find out mathematically the best way to go about searching for something with geophysical tools or other sensors so that we could potentially train a robot to do the work.’

What Nigel and his fellow researchers discovered was that dogs behaved as expected when well trained and working within their operation boundaries. However, when perturbed or when the connection with their trainer was broken in some way, dogs became confused and behaved differently and in an unpredictable manner.

‘So, this is one of my big interests now: AI and machine learning. We have massive amounts of data, but machine systems are only as good as the algorithms with which they are programmed or the people who are training them to do what they need to do. When a robot or a machine comes across something out of its normal operational boundary, it can get confused.

‘That takes me to how I finished my lecture – which is that we don’t need new geophysical tools or new “eyes”: we need to better interpret the tools we have already. In a way, it’s our thinking that has to be the new tool.’