Exploring the massive potential for innovative underground construction technologies in the US

Patrick Lane-Nott, Director of Engineering at hyperTunnel

The US underground construction industry is booming. 

Back in November 2021, President Biden signed into law a new $1.2tn (£895bn) infrastructure bill that has uplifted the prospects of construction players across the country. Described as a “once-in-a-generation” initiative, the bill helps to pave the way for a variety of ambitious projects.

Chief among these is the new railroad tunnel set to be built under the Hudson River that will connect New York and New Jersey as part of Amtrack’s Gateway Program, while the bill has also renewed talk of connecting New York and Boston with a high-speed, 16-mile
railroad tunnel. 

However, there are many similar flagship projects scattered across several states that are also coming to fruition.

The $6 billion Second Avenue Subway Phase II project is also currently underway in New York, while Baltimore is set to benefit from both the $6 billion Baltimore & Potomac Tunnel Replacement and $10 billion Superconducting Maglev Project – Northeast Corridor project. Meanwhile, over on the West Coast, the $5.5 billion Silicon Valley Santa Clara Extension and $12-15 billion BART 2nd Transbay Tube continue to capture headlines in California, while Texas is set to benefit from its own $1.7 billion D2 Subway in Dallas. 

With that said, not all underground structures currently being built in the US are designed for large scale transportation purposes.

The state of Washington is coming under pressure to address the impacts that man made structures are having on several endangered species of salmon, paving the way for the construction of several small tunnels that provide the fish free passage to migrate to the sea and back inland to spawn.

Back in California, meanwhile, to address the threat of tree branches falling on power lines and creating forest fires, Pacific Gas and Electric has outlined plans to bury 10,000 miles of distribution and transmission lines in California at a cost of $15-30 billion. 

Taking a new approach to underground construction

In every one of these projects, the sums involved are astronomical–and that presents a significant opportunity for innovation and
industry disruption. 

For well over a century, approaches to underground construction have broadly remained the same, involving the use of tunnel boring machines (TBMs). However, this conventional practice of excavation and building comes with risk, complexity and cost, as well as a heavy carbon footprint.

If we consider Pacific Gas and Electric’s own commitment, burying lines underground currently costs $1 million per mile – this is significantly more costly than hanging lines overhead, and only increases further in more difficult terrain, such as mountainous areas. 

Finding ways in which to make the United States’ many new underground construction projects more affordable is therefore vital. 

Thankfully, technological advances promise to make the construction, extension, repair, and maintenance of underground structures significantly faster, cheaper, safer, less disruptive, and more environmentally friendly.  

Indeed, one method involves the use of swarm robotics and in-situ construction to offer the underground construction industry more options besides the traditional processes. 

This new method is described as follows. First, pilot bores are drilled and lined, and robots sent inside to inspect the geology. Core samples are taken, and the geology is scanned using ground penetrating radar (GPR). The result is a near perfect understanding of the entire tunnel length’s geology.

Using this data, a virtual model of the tunnel structure is developed: the digital twin. With AI and machine learning, the optimum build schedule can be designed to create a sound structure in the geology.

Once the structure profile is defined, a swarm of inexpensive bots is sent into the grid of lined bores to visit planned locations in order to drill and deploy chemistry according to the AI-generated design. Thousands of robots will be used, all controlled using swarm technology to 3D print the tunnel in much the same way that bees build a hive or termites build a mound.

The ‘bots carve precise chambers in the geology and these voids are then filled with suitable construction material. The cast, in-situ blocks interlock to create a permanent structure, block by block. The initial survey robots come back to inspect the construction, ensuring that the chemical has spread evenly and precisely matches the
digital twin design.

After a full structural inspection and geophysical scan has been completed, the underground space is then excavated, with no human underground intervention required at any point. In this sense, where the traditional method entails digging a hole and then building the structure, this approach sees the structure built first and the
hole dug afterwards.

The interior walls are prepared for final use, leaving a smart structure that can be monitored and maintained throughout its life.

The many merits of novel methods

Not only is this ultra-high-tech in-situ construction approach scalable, making it suitable for small- and large-scale projects alike, but it also offers several major advantages. 

Costs are far lower than alternative building methods because construction takes place across the entire structure at the same time, dramatically enhancing productivity and reducing project  times.

Here, the use of robots is also key. Operating in parallel, they ensure many processes are performed simultaneously working throughout the structure all at the same time. This means that the duration of construction is determined by the number of bots deployed rather than by the length and difficulty of work alone. If projects need to be completed at speed, more bots can be deployed to
accelerate the process.

This construction method typically uses less energy, materials, and water, too, while waste and pollution are equally minimized. And that also goes for repair and remediation works. In addition, worksites are smaller, while the spoil from the tunnel interior is uncontaminated and therefore easier to use locally without processing.

Project risk is also reduced, and safety greatly enhanced. Until now, understanding ground conditions ahead of major works in detail has been extremely difficult, yet not knowing what you’re dealing with until you start digging can present major problems. This innovative approach provides geological certainty. 

It’s also an ideal solution when direct access from above ground isn’t possible or desirable for a new build or repair, such as in urban and highly built-up areas. The robots access the structure remotely so that critical infrastructure such as roads or railways do not necessarily have to be closed during work. 

Where sensors are installed in the ground during construction, ongoing monitoring and repairs can be achieved via a live digital twin, enabling the robots to continuously gather data sets and enhance their understanding. Not only does this enable better asset lifecycle management, but also enhances the swarm of robot’s ability to make decisions in every other project undertaken thereafter. 

Real-world applications of innovative underground construction technologies

Moving away from conventional construction methods, innovative processes such as these will only serve to enhance project sustainability, lower costs, reduce time to complete, and mitigate key risks – advantages that are key at a time the demands on underground transport and facilities infrastructure continue to grow.

In my view, the future of underground construction will be driven by swarm robotics. But exactly how far along this journey are we at this present moment?

At hyperTunnel, we’ve created a dedicated test facility in Basingstoke (UK) that is running robots on a 24/7 basis to continuously perform accelerated life-cycle tests to observe AI system responses and tolerance testing.

Such progress has led to several key successes, propelling our ability to support real-world projects.

In late 2022, the world’s first entirely robot-constructed underground structure – a six meter-long, two meter-high and two meter-wide ‘pedestrian-scale’ tunnel – was developed at our R&D facility as part of a project for UK rail infrastructure owner and operator Network Rail. We are now currently surveying a site for Network Rail to populate a digital twin in planning for some repair works. 

Further, the European Innovation Council (EIC), Europe’s flagship innovation program, has also backed the technology with €1.88 million in funding through its Accelerator scheme, while financial investment from VINCI – a global leader in concessions, energy and construction businesses has also been received. hyperTunnel has also received a grant through Innovate UK– at the Global Centre of Rail Excellence (GCRE) in Wales.

Looking ahead, hyperTunnel is currently engaged with numerous construction companies in the US, as well as in Canada, India, Japan, the Middle East, and of course Europe and the UK. With an eye to the US specifically, the merits of more effective underground construction methods will only continue to be amplified as urban populations grow, demands on transport infrastructure heighten, environmental challenges expand, and the ability to overcome geological challenges becomes clearer.

Be it speed, safety, sustainability, or cost– the potential benefits are already huge, and continually growing. Indeed, without question, the time has come to turn attention to the next generation of
underground construction.