Lateral thinking and technology transfer are set to revolutionise the construction of transportation and utilities tunnels, underpasses, car parks and other underground structures. Patrick Lane-Nott, director of engineering at hyperTunnel, explains how
When thinking about modern methods of construction, it’s tempting to focus only on how these might improve the construction process itself. Tempting, also, to think first of structures built above ground. But let’s broaden our minds for a moment.
Let’s go underground, where there’s an increasing need to take transportation and utility infrastructure because the world’s population is growing fast and too many cities are getting overcrowded. And let’s look at innovative new methods which not only improve the construction process itself – by reducing time, cost, and commercial risk – but also improve condition monitoring and maintenance so that whole-life costs can be lowered.
The size and number of underground construction projects commissioned around the world have traditionally been held back, of course, by high costs and high commercial risks. But forget that tradition. By replacing traditional methods – many of which have seen little fundamental change in 130 years – with revolutionary new alternatives, underground construction is poised to enter a new era. This means that projects previously considered prohibitively expensive can now be viable.
New techniques for constructing tunnels
The new methods I’ll introduce you to here have been conceived by British start-up hypertunnel, but don’t let that name confuse you – the company’s innovations can also help improve other types of underground construction. True, hyperTunnel’s main mission is to bring new techniques to constructing, enlarging, repairing, monitoring, and maintaining tunnels – but these techniques are also well-suited to the construction of underpasses and car parks, as well as burying power cables, rehabilitating water pipes, containing hazardous waste, fixing dams, and even securing coal tips and slag heaps.
First, though, hyperTunnel’s new techniques are being applied to tunnelling. Last year, Network Rail awarded the company a contract to work on non-disruptive tunnel repairs for the maintenance and improvement of the railway infrastructure, which includes some 650 Victorian-era tunnels across the UK. New approaches to this kind of work are expected to bring significant cost and delivery-time improvements, as well as greatly reduce inconvenience for passengers. In parallel with this work, hyperTunnel is running life-size simulations on a cross-passage of the type that will be needed 100 times by HS2 and 27 times by the Lower Thames Crossing.
Free-thinking and technology transfer are driving innovation. Though hyperTunnel’s techniques are either entirely new to underground construction or being applied more extensively than ever before, they have been proven in other industries with innovative digital technologies. In fact, the business’ co-founders, Steve Jordan and Jeremy Hammond, first saw the need to modernise tunnelling when jointly exploring a new approach to tidal-range energy. Now the company is borrowing and adapting concepts and technologies from industries as diverse as mining, oil and gas, chemistry and surveying, and Formula 1 motor racing.
As a result, underground construction is poised to take a quantum leap. We’re entering a new era of digital twins, 3D-printed structures, and the use of robots and swarm technology.
Building before excavating the underground asset
Whereas the conventional method is to dig a hole than build the tunnel or underground structure, hyperTunnel first builds the structure, then digs the hole. The structure is constructed in the ground before the underground asset is excavated.
Another significant break from convention is that the hole in the ground is not created by pushing through with a cylindrical boring machine or by drill-and-blast. Instead, the tunnel or hole is 3D-printed in the ground working to a fully parameterized 3D model (digital twin) of the tunnel or structure and surrounding ground.
This digital twin – supplemented by building information modelling – is created with a level of detail not previously seen in construction. Data is gathered by sending semi-autonomous robots and a proprietary 3D ground-penetrating radar system down a series of horizontal index bores. Seismic, tomographic, and thermal imagery data can also be meshed to add detail to the digital twin.
This is a big improvement over the current method of dropping vertical boreholes along proposed tunnel paths every several hundred metres or so – a distance over which geology can change. For the first time, a complete and detailed picture of ground conditions is created, removing any uncertainty about whether construction might encounter changes in geology, fissures, voids, or water. This eliminates the risk of delays and increased costs. What’s more, the unprecedented accuracy of hyperTunnel’s surveying and deployment methods is well-suited to dealing with a range of geologies. This will be especially advantageous if, as expected, the world’s increasing need for more tunnels, underpasses, and other underground structures means that more has to be constructed through challenging geologies or soft ground.
When this preparation work is done, the index bores are ready to serve as a skeleton or scaffold during construction, when construction bores are populated by robots known as hyperBots. These semi-autonomous machines are similar to those seen in other applications, such as warehouse picking and packing, bridge-building, and pipe maintenance and repair. By using swarm technology, they can greatly improve the efficiency and speed of underground construction.
Swarming hyperBots
To understand the concept of swarming hyperBots, think termites. Not as pests, but as highly efficient builders. These insects are hardly the most intelligent form of life, and yet, by working together in large numbers and behaving in ways programmed by their DNA, they manoeuvre around each other in a combined effort that reshapes earth into remarkably complex structures.
In much the same way, hyperBots are relatively simple (and inexpensive), yet when many populate the same construction site, they can get a huge amount of work done. When the hyperBots are sent into the construction bores, they are able to pass each other to move freely and to perform a wide range of tasks. Their actions are coordinated and monitored according to a construction plan created by the digital twin and artificial intelligence.
Using hyperSwarm technology managed by standard industry software, hundreds or even thousands of hyperBots can work simultaneously at different locations. They can handle data gathering, chamber cutting, micro deep-mixing cement, chamber evacuation and replacement, cleaning, delivering consumables, and the deployment into the ground of composite construction materials. And they can do all this in places where other machines would be too big or too costly, and where it’s potentially too dangerous for humans.
3D printing the tunnel or underground structure
hyperBots are used to form the shell of the tunnel or underground structure in an additive manufacturing process which uses the same principle as 3D printing. This concept – creating a three-dimensional object by imposing successive layers of material – will play a big role in future construction projects, overground and underground. It’s a versatile method of construction, capable of overlaying materials such as concrete, geopolymers, fibre, and sand, and of creating everything from small components and decorative elements to entire complex structures.
When hyperBots are tasked with deploying composite construction material into the ground (and later, perhaps also to spray a continuous concrete lining), each can carry a 20-litre cartridge of industrial chemicals which can be topped up by replenishing hyperBots. The exact deployment location, material strength, and chemical volume are determined by the construction plan. This provides for simple but accurate consolidation through to the precise manufacturing of the finished structure, building to higher standards than those achievable in a factory on the surface.
Best of all, this new method is fast and efficient: compared to traditional methods, 3D printing can reduce construction time by up to 70% and significantly cut material waste at job sites.
Long-lasting cost benefits
In a reversal of traditional methods, it’s only after the structure’s shell is complete that the untreated geology within the structure’s space is disrupted and excavated. Some of the index bores originally used for surveying the geology are now reamed-out to facilitate a slump of the spoil. The spoil is not dug or drilled but gathered and removed, which is much easier and requires significantly less energy. Removal is done in smaller spaces by a standard excavator, but for larger projects, there’s a new dragline shield technology, which utilises techniques used in open-cast mining.
These new methods of construction leave behind an infrastructure of pipes which really can be thought of as scaffolding – there to enhance asset-monitoring with cameras and sensors, and readily accessible by robots to conduct maintenance, repairs, or enlargement. And the existence of a highly detailed digital twin means that there’s a ‘single truth’ database of construction and geology data to enhance asset maintenance and management over the lifetime of the structure, reporting on its health every day. For condition-monitoring, maintenance, and containment of whole-life costs, these are game-changers.
The innovative new surveying, preparation, construction, and excavation techniques are game-changers too. Which no doubt has you asking how soon these advantages will be realised. I can partly answer that by confirming that work on the first completely new tunnel built with hyperTunnel’s techniques is expected to start next year. And I can partly answer it by disclosing that, in addition to the agreement with Network Rail, hyperTunnel is currently engaged in serious talks with a number of states, construction companies, and project leaders in the USA, Canada, India, Japan, the Middle East, and the UK. So watch this (underground) space!
