For much of the history of construction, the ground has been treated primarily as a constraint.
It is something to investigate, excavate, stabilise, retain and design around. Geotechnical engineering has become exceptionally good at understanding these challenges and managing the risks they present.
But that is only part of the story.
The ground should no longer be treated only as a constraint on development. It should be understood as a strategic resource for sustainable and resilient cities.
This is not a future possibility. The underground is already being used in ways that deliver energy, infrastructure, storage, resilience and environmental value. What is changing is our understanding of the scale of that opportunity — and the need to bring it into mainstream planning and investment decisions.
For many years, my own research has explored the interaction between infrastructure, energy and the ground. This work has shown that structures we need to build anyway can perform additional functions, creating value beyond their conventional purpose.
More recent research into the thermal environment beneath cities has added another dimension to this picture. Buildings, transport systems and underground infrastructure continually release heat into their surroundings. In dense urban areas, some of that heat accumulates below ground.
This can create engineering challenges. But it also raises a much more interesting question: if energy is accumulating beneath our cities, why should we regard it only as a problem?
Some of it can potentially be recovered and reused.
That simple shift in perspective captures a much larger opportunity.
From managing constraints to creating value
Sustainable construction is often framed around reducing impact: using fewer materials, lowering carbon emissions, consuming less energy and minimising environmental disturbance.
All of these objectives are essential. But sustainability should also be about extracting more value from the infrastructure and natural systems we already use.
A foundation does not have to provide structural support alone. A tunnel need not be considered solely as a transport corridor. Underground spaces, structures and geological formations can potentially perform several functions over their lifetime.
We already see this in practice. In Alabama, compressed air has been stored in an underground salt cavern for electricity generation for more than three decades. At Vienna’s Taborstraße metro station, underground structural elements have provided heating and cooling since the station opened in 2008. In Tokyo, vast underground reservoirs and tunnels are used to store stormwater and protect the city from flooding. These are very different applications, but they point to the same broader shift: the ground can provide value far beyond simply supporting what we build above it. The important point is that we should not limit our thinking to the applications we know today. Research and technological development are continuing to reveal new ways in which the underground can contribute to the cities above it.
This is not a field waiting for proof that value exists. That value is already being demonstrated. The frontier now lies in understanding how much more can be achieved and how these opportunities can be incorporated into mainstream construction and infrastructure.
A different question at the beginning of every project
The greatest change required may therefore be one of mindset.
Too often, the underground enters a project through questions such as: What are the ground conditions? What risks do they create? How difficult will excavation be? What type of foundations will be required?
These are essential questions.
But they should increasingly be accompanied by another: What can the ground contribute?
That question needs to be asked early.
If the potential of the subsurface is considered only after the major decisions about a building, transport system, energy network or urban development have already been made, many opportunities will inevitably be lost.
Governments and cities can consider underground resources as part of long-term infrastructure, energy and climate strategies. Developers and infrastructure owners can assess the value that subsurface assets may provide over decades rather than focusing only on initial construction costs. Architects, planners and engineers can consider above-ground and below-ground systems together. Contractors can help translate these ideas into solutions that are practical, scalable and economical.
This is also why geotechnical expertise needs to be present much earlier in the planning process.
As President of the International Society for Soil Mechanics and Geotechnical Engineering, I believe our profession has an important role to play in this transition.
Geotechnical engineering will always be fundamental to managing ground-related uncertainty and ensuring the safety of infrastructure. But its contribution can extend far beyond solving problems once the main parameters of a project have already been established.
Our knowledge of the ground can help shape those parameters in the first place.
A strategic resource beneath our feet
The pressures facing cities are substantial. Urban populations continue to grow. Infrastructure is ageing. Energy systems must decarbonise. Climate change is increasing the need for resilience. Space, particularly in dense cities, is becoming increasingly valuable.
The underground intersects with all of these challenges.
We already possess many of the engineering tools needed to begin exploiting its potential more intelligently. At the same time, continuing research will undoubtedly identify possibilities that are not yet part of conventional construction practice.
The opportunity is therefore both immediate and expanding.
The next step is to move this thinking beyond individual technologies and individual projects. The underground needs to become part of the strategic conversation about how cities are planned, how infrastructure is financed and how sustainability and resilience are delivered.
That requires governments, designers, engineers, contractors, owners and researchers to look below ground earlier and with greater ambition.
For too long, we have asked primarily how the ground might limit what we want to build.
The more important question for the future is what the ground can enable us to achieve.
The ground should no longer be treated only as a constraint on development. It should be understood as a strategic resource for sustainable and resilient cities.
