Sinkholes are the stuff of nightmares. The ground opens without warning in the middle of the night, a dark abyss indifferent to what’s above it. People wake up the next day to find a yawning chasm where their car, or their swimming pool, or the neighbouring house used to be
In 2007, a giant 150m-deep sinkhole in Guatemala City swallowed close to 20 homes and left three people missing. In the UK, a spate of collapses in 2014 left people questioning whether human activities underground – including controversial practices such as fracking – could be to blame.
The jury is still out on that front, but, with an ever-growing focus on the environmental issues around new projects, particularly in the energy sector, engineers need to be constantly mindful of the impact their activities could be having on the planet.
Fortunately, technology is here to help. Earlier this month, researchers at the University of Nottingham created a map of relative land motion for Scotland. Using hundreds of images from the Sentinel-1 satellite, taken every six days, it has built up a picture of whether land is subsiding or rising with sub-centimetre accuracy.
Satellite technology has been used to measure subsidence in urban areas, but this is the first time it’s been achieved in rural areas. They have been tricky until now because they’re not as reflective as concrete, metal and glass, and because the reflectiveness of a particular field can change drastically with the seasons.
The new, software-based technique could have important applications in the onshore oil and gas industry, says Andrew Sowter, the chief technology officer of spin-out company Geomatic Ventures, which is commercialising the technology.
Slipping and rising
“We can use this technique to look at reservoirs that are used for gas extraction or storage and we can measure the effect on subsidence,” he tells Professional Engineering. “In Scotland, we’re seeing that the earth is moving quite a lot due to pre-existing activities such as coal mining. We see that coal mines are still causing collapse and uplift across the UK.”
Although fracking is banned in Scotland, Geomatic’s technique could be informative in other areas where residents may have concerns about projects. “You can identify where the subsidence or uplift is correlated with your activities, and that tells you more about the efficiency of your process,” says Sowter.
The technique could also be used for infrastructure projects such as the HS2 high-speed rail scheme, according to University of Nottingham researcher Stephen Grebby. “Our wide-area monitoring technique could be used to help identify and monitor ground instability issues along the whole stretch of the proposed HS2 route,” he says.
“This would provide information that could ultimately influence the plans for the final route for phase two of HS2, or at least highlight existing ground instability issues that may need to be addressed during construction of the network.”
At the moment, companies have to rely on ground-based techniques which makes it difficult to cover large areas. Others have used artificial reflectors in fields to enable satellite imagery. Although Geomatic Ventures’ images can measure changes of depth extremely accurately, they’re relatively coarse in terms of resolution, but there are benefits. “We don’t actually have to go out there,” explains Sowter. “Our business model is a cheap way of screening a whole area, and, if you’re particularly concerned about a particular well or pipeline, it’s better to use our surveys to focus your efforts rather than to try and survey the whole thing.”
Technology can also help in the planning stages of projects, particularly when it comes to selling large, complex and potentially disruptive schemes to the public. Altrincham-based company 3DWebTech makes interactive computer models of large-scale constructions, particularly in the energy sector where it has worked on all four of the UK’s new nuclear projects.
At the Nuclear New Build Conference at London’s County Hall earlier this year, director Andy Dennison demonstrated 3DWebTech’s work on Moorside, a power station proposed by NuGen for Cumbria’s west coast.
The company created a full 3D model of 7,000 square miles of the Cumbrian countryside, including the proposed layout of the site, with new roads, worker accommodation and a railway station. NuGen then used the 3D model during the consultation period, showing it to local residents who were able to jump into it in virtual reality to determine what the power plant would look like from their houses. “People can see what it will look like from their back garden,” says Dennison.
He says the technology helps to convince local residents that the projections they’re seeing are a “true and fair” reflection of what the finished site will look like. “We’re trying to remove some of the ambiguity and misunderstanding,” he says.
The 3D models can also be populated with information from suppliers and contractors to create a timeline of how the different stages of construction will affect different parts of the community, whether that’s noise from trucks driving down an access road, or cranes on the horizon.
“If you don’t engage with the community, they can provide a challenge to you,” said Alistair Smith, nuclear development director at Costain, at the conference. “We’ve been trying to encourage the developers to not just show the pretty picture,” he added. “It’s better to be honest about what it’s going to look like.”
As well as helping engineers to assess the environmental impact of projects, and showing residents the potential effects of their plans, technology could also be used to make sure that big firms keep their promises. Sowter mentions the Crystal Rig windfarm in the Scottish Borders – where Geomatic spotted an area of uplift on its land movement map.
When the windfarm was built in the early 2000s, foundations had to be dug into the peat to anchor the turbines, but landowners and locals were promised that there would be no long-term damage. Now the ground is recovering.
“The fact that we saw uplift is evidence they’re doing what they said they would – they’re being environmentally friendly and they’re trying to recover any problems that they caused during their activities,” says Sowter.
New developments could usher in an era of environmentally responsible engineering. “Using our technology and others,” concludes Sowter, “we can say to companies: ‘Here’s what you need to do to prove that you’re not affecting the environment’.”
Picture credits: 3dWebTech / University of Nottingham / Geomatic Ventures
Content published by Professional Engineering does not necessarily reflect the views of the Institution of Mechanical Engineers