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Smart tunnelling

Atkins | 02 Mar 2015 | Comments

Soaring urbanisation, increasing transport demand and rapidly rising land prices are behind an upsurge in tunnelling projects around the world.

Space in cities is at an ever-increasing premium. With cities now expanding at the rate of one million people per week, the demand for underground infrastructure – such as railways, roads and utilities – is on the rise.

“Cities lack space but there’s no shortage of space underground,” notes Paul Groves, Atkins’ head of tunnelling. “And it’s often cheaper to build below ground than it is to carve up the streets and demolish buildings.”

Creating infrastructure below ground has clear benefits. First, it reduces pressure on valuable surface land, freeing up space for buildings and open spaces. Underground “land” is cheap: in the UK, for example, subsoil acquisition payments to landowners for land deep below the surface can be as little as £50.

Second, tunnelling is less disruptive than building at ground level. Most tunnelling today is carried out using tunnel boring machines (TBMs). It’s the engineering equivalent of keyhole surgery: once access shafts have been sunk and the TBMs put to work, nobody knows they are there. That means business as usual at street level, with no noise nuisance, dust or traffic jams.

Tunnelling renaissance

Cities all over the world are looking below ground in the race to build high-capacity metro systems. Underground rail networks play an important role in combating congestion and spurring economic development – all achieved with minimal land take.

The Middle East is one region where tunnelling know-how is in high demand. Ten years ago, the Middle East had no railways at all. Today, it is the crucible of an urban transport revolution, with governments embarking on ambitious metro projects in the battle to combat car dependency.

The Dubai Metro in the United Arab Emirates is a good example. The 75km network, the world’s longest fully-automated railway, includes more than 12km of tunnels – the first major bored tunnels in the Gulf. Atkins provided detailed tunnelling design for the project, as well as geotechnical and site investigations, viaducts, bridges and specialist services.

“The Middle East is going through a major expansion in its underground facilities and it is a very important market for us,” says Groves. “The rise of metro systems in the region is unprecedented because there are so many of them in one place.”

Elsewhere in the region, Atkins is lead designer for three of the six lines of Saudi Arabia’s planned Riyadh Metro, the largest public transportation project in the world. Atkins is also leading the design of the Gold Line and Red Line South projects, part of the new Doha Metro in Qatar, comprising 32km of underground route.

Demand for tunnelled infrastructure in East Asia is also buoyant. In Hong Kong, Atkins worked on the creation of two key routes – the West Island Line and the Express Rail Link. The works included excavation of deep rock tunnels beneath the highest mountains in Hong Kong.

In the UK, meanwhile, work on the Crossrail project in London is now well advanced, with principal work on the 21km of underground route that comprise the new east-west route nearing completion. Atkins was recently selected as route developer for London’s Crossrail 2 programme to provide a new southwest-northeast link for the UK capital.

In depth

Aside from economic and social drivers, advances in tunnelling technology also make going underground an increasingly attractive and cost-effective option.

“The technology around tunnelling methods is continually improving. We can tunnel safely and with limited disruption to the public and to structures,” says Groves.

Improved materials are also helping, such as tunnel linings – the concrete panels that form the inside layer of freshly excavated bores.

“Better concrete and better reinforcement are helping to reduce costs,” says Groves. Better supply chains also make a difference: “The industry is now able to routinely supply concrete that is stronger than it was 20 or 30 years ago. As a result, we don’t have to worry about pushing the limits so much.”

Changes likes these are helping railway builders to open up parts of cities that were once geological no-go zones. The east of London is a case in point. Most of London’s original deep-level tube lines are concentrated in the easily-excavated clays that lie north and west of the city. But in the east, it’s a different story. The underlying Thanet Sand – a silty, fine-grained sand deposited 60 million years ago – kept the railway builders at bay for decades. Not any more.

“Tunnelling in the Thanet Sand was more difficult,” says Groves. “That’s one of the reasons the underground network is less prevalent in the east. Using current technology, though, there is no particular concern with tunnelling in sand in an urban area. Things are very different from what they were 20 or 30 years ago.”

It’s not only hardware improvements that are transforming tunnelling. Digital collaboration tools also make a difference. One of these is Building Information Modelling (BIM), a 3D modelling technology that takes every aspect of a design or project into account. BIM provides designers, engineers and contractors with access to data throughout the life of the asset.

“With respect to underground space use, the rise of digital technology has made a big difference,” says Groves. “When it comes to accommodation of stairs, escalators, fire and life safety systems, power cable and drainage, the use of BIM means that clashes and other issues are almost entirely eliminated.”

As the critical mass of expertise and experience grows, the economic risks and uncertainties associated with tunnelling shrink. And with Atkins engaged in projects all over the world, the opportunities for knowledge sharing are significant.

“The reality is we don’t need to do too much blue sky thinking,” points out Groves. “What we really do is recycle great ideas and sound engineering solutions from our centres of tunneling expertise around the world and make step-by-step improvements tailored to different local circumstances. That’s particularly true of Atkins globally – all of those connections are important to us in the way that we act. International knowledge sharing and reuse is the key.”

Expertise is transferable not just across geographies, but between tunnels designed for different purposes. Atkins has extensive experience in the construction of tunnels for roads, water supplies, power distribution, sewage and stormwater systems.

Getting more

As well as new-build projects, refurbishment and expansion of existing tunnelled infrastructure is also part of the picture. In the United States, for example, Atkins provided construction management and general contractor services for the widening of the 1960s-built Interstate 70 Mountain Corridor near Idaho Springs in Colorado – one of the country’s strategic east-west road links.

In the UK, meanwhile, Atkins’ work on the Belfast sewers project and on London’s nineteenth-century Connaught and Thames tunnels highlights the company’s ability to provide a new lease of life for ageing Victorian infrastructure.

In addition to upgrades, there’s also growing interest in replacing existing above-ground assets, such as road flyovers, with new tunnelled infrastructure. While the prospect of traffic-free towns is remote, tunnelling could eliminate at least some urban eyesores. In the US, Boston’s “Big Dig” – a $15bn project to replace an elevated urban highway with a tunnel – has attracted international attention.

“The technology’s all there – such projects have been built in various locations not just in North America but in the Far East as well. We’re working on a very large road tunnel in Hong Kong at the moment,” says Groves.

Road tunnelling is expensive. But Groves stresses the need to look beyond the initial price tag and to take whole-life costs into account.

“If you eliminate a road flyover, that land can be used for something else and there’s clearly an enormous value in that. There’s also the question of maintenance: concrete structures in the open environment, such as flyovers, require significant amounts of structural maintenance. That’s not the case with tunnels. When you start to take those sorts of things into account, it doesn’t seem so expensive.”

In the realm of railways, technology available to end customers is also helping to tip the economics in favour of tunnels. High-capacity signalling such as CBTC – communications-based train control – means that operators can run more trains, more frequently, right from the start. That’s one of the reasons why a tunnel built in 2015 is capable of carrying up to 30 per cent more traffic than one constructed in 1980.

Political interest in capitalising on tunnelling expertise is growing. In the UK, where the Crossrail project is in its final leg, the government recently announced funding worth £1.1m to develop tunnelling skills with the construction industry providing an additional £1.7m. The money will be used to create apprenticeships and train tunnelling workers.

The future for tunnels is bright, thinks Groves: “Tunnels deliver huge benefits for society. The coming years are likely to see a far greater use of underground space, not only for railways, roads, water and sewers but also for the storage of crude oil and gas. There is also a need for long-term nuclear waste depositories.”

And he believes today’s tunnelling projects deserve wider public recognition: “People talk a lot about the achievements of the great Victorian engineers and I am an admirer of the work they did,” he notes. “But to be honest, what we do now is far more impressive.”

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