Making Problematic Ground Safe
Professor Ian Jefferson’s fascination with the ground beneath our feet began when he was a young boy growing up in west London. He loved digging holes and building things, but it was a ‘disappearing hole’ in the playground at primary school that really caught his imagination.
‘Over a period of a couple of years I noticed that on a grassy area, by a tree, the ground opened up in summer and closed up in winter,’ he recalls. ‘I now know that it was due to the swell-shrink characteristic of London clay, but at the time I had no idea why was happening and it really sparked my curiosity.’
Today, Ian is an international expert in why the ground shifts and – at times – collapses, often at great financial and emotional cost, and is involved in engineering new and smart techniques to make it safe. His research spans ground instability caused by mining in the UK to soil erosion in China.
He is a passionate advocate of raising public and political awareness of the importance of improving and safeguarding problematic ground, especially with growing and ever-changing demands on our infrastructure.
‘The functionality of society is controlled by and depends on how the ground behaves, because all buildings and infrastructure sit on or in the ground,’ explains Ian, who is Professor in Geotechnical Engineering. ‘Even planes need the ground to take off from; it is really fundamental to everything we do.’
And yet, he points out, terra firma tends to get taken for granted until something catastrophic happens, such as a major landslide or the spate of sinkholes that have swallowed cars and houses across parts of the world.
But the ground is challenging to deal with, and ageing infrastructure such as roads and rail embankments adds another layer of problems.
‘So to understand and successfully engineer the ground, it’s essential to overcome its problematic behaviour,’ says Ian, whose Inaugural Lecture was entitled ‘Too loose or not too loose: making problematic ground safe’. ‘To do this safely, effectively and economically requires an understanding of how the ground was formed, how this impacts behaviour and affects any interventions designed to overcome such behaviour.’
The difficulties posed by problematic ground, in particular collapsible and expansive soils, and how to mitigate them for today’s and future demands is a huge challenge that requires new approaches.
Developing electrokinetic stabilisation (EKS)
One such approach that Ian and his team are working on with industrial partners is electrokinetic stabilisation (EKS).
‘Essentially it’s putting an electrical current into the ground and moving chemicals around. This changes the chemistry of the soil and helps to stabilise it.’
Working with Bristol-based Foundation Piling Ltd and Birmingham-based Amey, EKS is being tested on ground such as unstable ground associated with subsidence impacts on residential housing. ‘The EKS technique reduces this behaviour characteristic by changing the chemistry of the clay soil.’ Having successfully tried out the technique on insurance-blighted residential land, Ian says he is confident works. ‘The next stage is getting it to proof-of-concept, and to do that we are looking to get funding through various organisations to do that.’
This work is also under development to extend to the treatment of unstable slopes, many of which are found on our road and rail networks
‘A lot of our infrastructure is at the end of its use-by date,’ says Ian. ‘Our road and motorway network is a good example. A lot of it, such as the M5 motorway, is 30 to 40 years old or more and the embankments, where soil has been artificially placed, is starting to move. It’s not catastrophic, but it has to be addressed.’
Smart monitoring systems
Ian, who has been at Birmingham since 2004 and has been awarded more than £15m worth of grants, is also working on smart monitoring systems that would not only alert engineers to a problem, but also solve it.
‘These are devices that measure electrical properties of the ground, monitoring changes in the ground and kicking in when it detects them – so sort of self-correcting.’
Such devices could be crucial to addressing a range of problems caused by ground vulnerability. Underground pipes are a good example.
‘Thanks to the Victorians, we’ve done nicely, but the stock is old now and we have to look to the future. There’s a lot of focus on leaks from pipes, which is to do with pipe interaction with the ground it’s in. Where the leak is might not be where the problem is, so we’re trying to understand what parts of pipes are vulnerable and how that changes with time. And what we need is for the pipe to tell us there’s a problem – so a smart system again. The grand plan is to develop systems that are not only smart enough to tell us there’s a problem, but also to seal themselves.’
Ian, who works with the British Geological Society, stresses that while investment in new infrastructure is all well and good, it is vital to also protect and improve – and where necessary make safe – what we have now.
Ian’s long-term ambition is to ‘move things forward’ in terms of public and political understanding of the importance of maintaining the infrastructure.
‘There has been a shift in government towards building new infrastructure, but the problem we have now is our existing stock. We still have to live; we can’t wait ten or 15 years for something new to be built. It’s about demand and supply. For example, electricity: we’re using a lot more than we were, so how do we distribute that electricity safely? So there are all these sorts of challenges.
‘But I think the mood has changed in this country. A few years ago the gravitation was towards business, but engineering is coming back to the fore. That is heartening, because it has a very important role to play.’
Find out more