Radical new methods for underground construction

Lateral thinking and technology transfer are poised to revolutionize the construction of transportation and utility tunnels, underpasses, parking lots and other underground structures. Patrick Lane-Nott, director of engineering at hyperTunnel, explains how

When thinking about modern building methods, it’s tempting to focus only on how these might improve the building process itself. Tempting, too, to think first of structures built above ground. But let’s broaden our minds for a moment.

Let’s go underground, where there is a growing need for transportation and utility infrastructure because the world’s population is growing rapidly and too many cities are overcrowded. And let’s look at innovative new methods that not only improve the construction process itself – reducing time, cost and business risk – but also improve condition monitoring and maintenance so that costs over the life cycle life may be reduced.

The size and number of underground construction projects commissioned around the world have traditionally been held back, of course, by high costs and high business risks. But forget this tradition. By replacing traditional methods – many of which have seen little fundamental change in 130 years – with revolutionary new alternatives, underground construction is about to usher in a new era. This means that projects previously considered prohibitive can now be viable.

New tunnel construction techniques

The new methods I’m going to present to you here were dreamed up by the British start-up hypertunnel, but make no mistake about the name, the company’s innovations can also improve other types of underground construction. Admittedly, the main mission of hyperTunnel is to bring new techniques for the construction, expansion, repair, monitoring and maintenance of tunnels – but these techniques are also well suited to the construction of underpasses and car parks. , as well as burying electrical cables, rehabilitating water pipes, containing hazardous waste, fixing dams and even securing coal dumps and waste dumps.

However, the new hyperTunnel techniques are first applied to tunneling. Network Rail last year awarded the company a contract to work on non-disruptive tunnel repairs for the maintenance and improvement of rail infrastructure, which includes some 650 Victorian-era tunnels across the United Kingdom. New approaches to this type of work should bring significant improvements in terms of costs and delivery times, as well as considerably reduce inconvenience for passengers. In parallel with this work, hyperTunnel is carrying out full-scale 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 drive innovation. Although hyperTunnel techniques are either entirely new to underground construction or applied more widely than ever before, they have proven themselves in other industries with innovative digital technologies. In fact, company co-founders Steve Jordan and Jeremy Hammond first saw the need for tunnel upgrades when they jointly explored a new approach to tidal power. Today, the company borrows and adapts concepts and technologies from industries as diverse as mining, oil and gas, chemicals and surveying, and Formula 1 motor racing.

As a result, underground construction is about to take a leap forward. We are entering a new era of digital twins, 3D printed structures and the use of robots and swarm technology.

Build before digging underground asset

While the conventional method is to dig a hole and then build the tunnel or underground structure, hyperTunnel first builds the structure and then digs the hole. The structure is built into the ground prior to excavation of the underground asset.

Another significant break with convention is that the hole in the ground is not created by pushing with a cylindrical boring machine or by drilling and blasting. Instead, the tunnel or hole is 3D printed in the ground based on a fully parameterized 3D model (digital twin) of the tunnel or structure and the surrounding ground.

This digital twin – complete with Building Information Modeling – is created with a level of detail never seen before in construction. Data is collected by sending semi-autonomous robots and a proprietary 3D ground-penetrating radar system down a series of horizontal index boreholes. Seismic, tomographic and thermal imagery data can also be meshed to add detail to the digital twin.

This is a vast improvement over the current method of digging vertical boreholes along proposed tunnel routes every few hundred meters or so – a distance over which the geology can change. For the first time, a complete and detailed picture of ground conditions is created, removing any uncertainty as to whether construction might encounter changes in geology, cracks, voids or water. This eliminates the risk of delays and increased costs. Additionally, the unprecedented precision of hyperTunnel’s surveying and deployment methods is well suited to handle a range of geologies. This will be particularly advantageous if, as expected, the world’s growing need for more tunnels, underpasses, and other subterranean structures means that more must be built through difficult geologies or soft ground.

When this preparatory work is complete, the indexed bores are ready to serve as skeletons or scaffolding during construction, when the construction bores are filled in by robots called hyperBots. These semi-autonomous machines are similar to those used in other applications, such as warehouse picking and packing, bridge construction, 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 hyperBots swarming, think of termites. Not as parasites, but as very efficient builders. These insects are not the most intelligent life form, and yet, working together in large numbers and behaving in ways programmed by their DNA, they maneuver around each other in a combined effort that reshapes the earth into structures. remarkably complex.

Similarly, hyperBots are relatively simple (and inexpensive), but when many populate the same construction site, they can accomplish an enormous amount of work. When the hyperBots are sent into the construction boreholes, they are able to cross paths to move freely and perform a wide range of tasks. Their actions are coordinated and tracked according to a construction plan created by the digital twin and artificial intelligence.

Thanks to the hyperSwarm technology managed by standard industrial software, hundreds or even thousands of hyperBots can work simultaneously in different places. They can handle data collection, chamber cutting, deep micro-mixing of cement, chamber evacuation and replacement, cleaning, delivery of consumables, and in-ground deployment of building materials composites. And they can do all of this in places where other machines would be too big or too expensive, and where it’s potentially too dangerous for humans.

3D printing of the tunnel or underground structure

HyperBots are used to form the envelope of the tunnel or underground structure in an additive manufacturing process that uses the same principle as 3D printing. This concept – creating a three-dimensional object by imposing successive layers of matter – will play a big role in future construction projects, above and below ground. It is a versatile construction method, capable of layering materials such as concrete, geopolymers, fibers and sand, and creating everything from small components and decorative elements to entire complex structures.

When the hyperBots are tasked with deploying composite building materials into the ground (and later, perhaps also spraying a continuous concrete overlay), each can carry a 20-liter canister of industrial chemicals that can be refilled in restocking hyperBots. The exact deployment location, material strength, and chemical volume are determined by the construction plan. This allows for simple yet precise consolidation through to precise fabrication of the finished structure, building to higher standards than achievable in an above-ground factory.

Even better, this new method is fast and efficient: compared to traditional methods, 3D printing can reduce construction time by up to 70% and significantly reduce material waste on construction sites.

Sustainable economic benefits

In a reversal of traditional methods, it is only after the shell of the structure is completed that the untreated geology within the space of the structure is disturbed and excavated. Some of the index boreholes originally used to study the geology are now reamed to facilitate subsidence of the cuttings. Spoil is not dug or drilled but picked up and removed, which is much easier and requires much less energy. Removal is carried out in smaller spaces by a standard excavator, but for larger projects there is new dragline shield technology, which uses techniques used in surface mining.

These new construction methods leave behind a pipe infrastructure that can truly be considered scaffolding – there to enhance asset monitoring with cameras and sensors, and easily accessible by robots to perform maintenance, repairs or enlargement. And the existence of a highly detailed digital twin means there is a “single truth” database of construction and geology data to improve maintenance and asset management throughout the life of the structure, reporting on its health on a daily basis. For condition monitoring, maintenance and lifetime cost control, this is a game-changer.

New and innovative surveying, preparation, construction and excavation techniques are also changing the game. Which undoubtedly makes you wonder how soon these benefits will be realized. I can partly answer this by confirming that work on the first completely new tunnel built with hyperTunnel techniques is due to start next year. And I can partially answer that by revealing that in addition to the Network Rail agreement, hyperTunnel is currently engaged in serious discussions with a number of states, construction companies and project developers in the United States. USA, Canada, India, Japan, the Middle East and the UK. So watch this (underground) space!

Bonny J. Streater