A journey through the underworld

Professor David Chapman delivering his Inaugural Lecture

The capacity audience at Professor David Chapman’s Inaugural Lecture were treated to his dramatic tunnel collapse experiment, which saw a replica of the Big Ben clock tower sitting atop sand in a Perspex box dramatically cave in and shoot through the entrance when the tunnel face support was removed. 

‘I did the experiment quite early on in the lecture and it seemed to go down well,’ smiles David, who is Professor of Geotechnical and Underground Engineering. ‘The point of the experiment was to demonstrate how a very simple idea, Brunel’s tunnel shield (a reinforced shield of cast iron in which miners would work in separate compartments, digging at the tunnel-face), can prevent a tunnel collapsing. The idea is still used today as the basis of many tunnelling operations.’

Model of Big Ben clock tower sitting in box of sand. Next to it is another box of sand without a tunnelling shield. The equipment was used to demonstrate how tunnelling shields prevent tunnels collapsingAbout 90 people attended David’s recent address, ‘A journey through the underworld’, which 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 research and career journey.  

‘I enjoyed it, although it was probably the most difficult lecture I’ve ever had to do, because it had to be pitched at colleagues and PhD students as well as those, such as friends of mine, who had no idea what I do for a living! But I think I managed to get the balance right.’ 

The lecture explored David’s remarkable ‘underground’ career spanning more than 25 years, which has turned academic ideas and research into real-life solutions for locating, maintaining and repairing the existing ‘buried treasure’ beneath our feet – in other words, the hidden infrastructure on which vital services such as water and gas supplies rely – and installing new underground utilities and building tunnels.

‘The key message of my Inaugural Lecture was that we know quite a lot about our above-ground urban environment: we can see it, we can interact with it and we can monitor it quite easily. But when it comes to our subsurface environment, we don’t really know much at all,’ he explains. ‘We bury lots of things, such as service pipes, to keep them out of the way, and quickly forget about them until something goes wrong – they break or leak. Because much of this underground infrastructure goes back many years, in some cases centuries, we have trouble knowing where it is and what condition it is in. We can’t see it and we don’t have instrumentation down there to tell us how the infrastructure is performing.

‘And when things do go wrong, the main problem we have is that the tools available are very broad-brush: they might be able to determine a leak – or leaks – as being in a particular housing estate, but not exactly where it is, and hence it takes time to find and fix.

‘So, a lot of what I do is about trying to improve our knowledge of the subsurface environment, such as developing sensors for pipelines – smart pipes, if you like – that can tell us remotely how things are changing underground. It means you don’t have to dig up the ground unnecessarily, so it’s cheaper and causes less disruption.’

For many years, David and colleagues at Birmingham have been at the forefront of forging new ways to map and assess the ‘underworld’ – with the long-term aim of making our cities more resilient and sustainable in the face of factors such as climate change and increasing traffic. Following the success of two ambitious projects, the University recently embarked on a major collaboration with industry called FINDIT (Finding Infrastructure with Non-Destructive Imaging Technologies). Co-led by David, it’s not only proving that it is possible to accurately locate buried infrastructure using geophysical methods such as ground penetrating radar and acoustic reflection methods, but also to determine the condition of these assets. The project, whose industry partners are RSK, Geomatrix and BT, recently won Best Collaborative Work at the Street Works Awards 2017

‘FINDIT came out of the previous two projects, Mapping the Underworld and Assessing the Underworld, and is addressing an industry challenge: BT was having problems looking for blockages to cable ducts,’ explains David. ‘They were trying to feed new fibres through existing ducting, but finding some of them were blocked because they were broken or damaged. They would put a rod up the duct, which would get stuck, indicating a blockage, but they couldn’t tell if it was one blockage or many. With situations like this, a company can get someone out to clear the blockage, then find another blockage and have to get someone out again, which is time-consuming and costly. We are showing that geophysical techniques – one we used in this project was an acoustic method: sending sound, essentially using a speaker, down the duct – can detect if there are multiple blockages and where they are.’ 

David, who came to Birmingham nearly 20 years ago, is also Technical Director of the National Buried Infrastructure Facility (NBIF), due to open at the University in 2019. Part of the UK-wide, government-funded project called UK Collaboration for Research in Infrastructure & Cities, the £28m NBIF is a ‘one of its kind’ facility for research, education and training in buried infrastructure-ground interaction. Its key feature will be a large pit that can be subdivided into smaller bays, with a moveable floor section to simulate subsurface ground displacements.

‘A major part of the Assessing the Underworld project was a trench trial that we did on campus, on land behind the old library. We dug two trenches, each 6m long, one of which we back-filled and surfaced very well. The other one, we back-filled to a much lower standard – although still within the specification required by current regulations for our roads. We put lots of instrumentation in there as well – and what we found was a significant difference between the two trenches, especially with the amount of water getting in. Water in the ground means it tends to soften and therefore weaken. 

‘Data from the trial, which was driven by companies and councils, is still being analysed, but we think it will prove very useful and possibly show that the lower end of the specification regulations aren’t really good enough, which may lead to change.’ 

The NBIF will enable these sorts of trials to be conducted even more effectively, says David.

‘We’ll be able to do a lot of things we can’t do now, because we will have a controlled environment. We won’t be reliant on the weather or the temperatures: we will be able to simulate whatever environment we need in order to carry out experiments at scale.’ 

David says the new facility is the result of two decades of hard work and innovative research. 

‘We were the obvious choice because of the work we’ve done over the past 20 years. Being awarded this project is really going to set the benchmark for the next 20-plus years.’