The Future of Tunnelling
In this article Professor Colin Eddie, Technical Expert Diales looks at the past, present, and future of tunnelling.
What’s the Bigger Picture?
Our planet is changing more rapidly than at any other time in human history. It took 200,000 years of human evolution to get to a population of 1bn by the 1800s; in the 200 years since we have seen a seven-fold increase, with the population expected to rise to 10bn by 2050 (Figure 1). Associated with this population growth is explosive urbanisation: in 1800, 3% of the world’s population lived in urban environments and by 2050, 70% of us will be city dwellers. Mega-cities are defined at conurbations of more than 10m people. In 1950 there was only one (New York) and today we are approaching 50, both in industrialised and in developing countries.
In 2015, the United Nations published its 17 Sustainable Developments Goals (SDGs), to address the global challenges we face, including those related to poverty, inequality, climate, environmental degradation, prosperity, and peace and justice (Figure 2).
As a civil engineer and tunneller, my eye is drawn in particular towards:
Goal 6 – Ensure availability and sustainable management of water and sanitation for all. The majority of the world’s population still lacks safe sanitation and 3 in 10 lack access to safe drinking water.
Goal 9 – Build resilient infrastructure, promote inclusive and sustainable industrialisation and foster innovation.
Goal 11 – Make cities and human settlements inclusive, safe, resilient and sustainable.
In 2018 the UN Published its progress report. The UN Habitat Executive Director stated “Cities are the spaces where all the SDGs can be integrated to provide holistic solutions to the challenges of poverty, exclusion, climate change and risks”.
Where are we today?
Associated with explosive urbanisation, we are seeing cities with inadequate shelter, insufficient infrastructure and services, overcrowded transportation systems, inadequate water supply and sanitation, increasing pollution and increasing consequences from natural disasters.
This all means one thing: we are rapidly running out of space and this is fuelling an insatiable appetite to utilise the space beneath our feet. The tunnelling and underground space sector is currently estimated to be worth US$100bn per annum and at 7% growth per year is one of the fastest growing sectors of the construction industry.
Today however the cost of tunnelling, particularly on major projects is much higher than it needs to be in many parts of the world and perversely often in those countries with the most “mature” construction industries.
In recent years we have seen major tunnelling projects suffer significant and unnecessary cost over-runs due to poor procurement choices compounded by poor contract administration. Tunnelling projects are often procured using an incomplete reference design which is then to be developed by a design and construct entity. All too often however, tensions exist in this procurement process between the reference design, planning conditions, the Client’s unnecessary technical specifications and the functional requirements for the project. Couple this with excessive red tape, multiple tiers of management, a lack of a controlling mind and excessive man marking, and we have the perfect storm. FIDIC has responded to the tunnelling market and recently introduced its Emerald Book; a contract it considers to be balanced in terms of risk allocation. Let us hope so.
In many countries (including the UK) planning of underground space is extremely poor or even non-existent. No effective space reservation policies exist, and no single body is responsible for the coordination of underground space. Space is therefore allocated on a first come first served basis with no coordinated plan for the future. In cities such as London this will inevitably mean that future tunnels will be driven at ever increasing depths.
Despite significant improvements in tunnelling technology in recent years we are still essentially scratching at the ground with tools that all too quickly wear out and then invariably supporting the ground with conventional concrete made from Portland Cement (one of the least sustainable construction materials, which is currently responsible for about 8% of the yearly global CO2 emissions).
New thinking is desperately required. The efficient and sustainable development of underground space is imperative if we are to maintain or even arrest the decline of the quality of the lives of our urban populations. In Elon Musk’s inimitable fashion, he recently challenged the world’s tunnellers to reduce the cost of tunnelling by 90%. A headline grabbing soundbite no doubt, but actually a more legitimate aspiration than you must at first think. If we are able to implement emerging technologies together within more effective contractual frameworks, a big bite could be taken out of this 90%. If we sprinkle over the top, effective and pro-active risk management strategies, then confidence in the out-turn delivery will also be greatly enhanced thereby improving much needed public and investor confidence in the future.
Emerging Technologies
New and innovative technologies will bring about a paradigm shift in tunnelling in the near future. Today many tunnels are constructed using tunnel boring machines (TBMs).
These impressive machines are armed at the face with picks or discs and these wear as they excavate the ground. Delays associated with change of these cutters are often expensive and sometimes hazardous. Contactless excavation techniques would reduce or even eliminate wear and greatly enhance production rates and research is currently underway to bring this concept to market.
In tunnelling the adage that “time is money” is extremely apposite. Continuous excavation techniques utilising extruded linings would greatly increase the speed of construction and reduce costs significantly. The extruded lining method has been used off and on for nearly 40 years but with limited success due to the use of conventional concrete and steel bar reinforcement. New materials have already been developed that have been engineered at a nanoscale to deliver unbelievable performance when compared with conventional construction materials. These materials would be ideal for extrusion and as they are also self-healing and ultra-ductile would deliver exceptional performance and longevity.
Future Tunnelling and Underground Space Applications
A number of exciting new applications for underground space will soon be making a major impact on communities around the globe. We shall explore a couple of these.
High-Speed Travel
Travelling at high speed through the air at atmospheric pressure is highly energy inefficient. Drag is proportional to the cube of the speed and this explains why supercars have needed to double their horsepower to achieve top end speed increases of only a few kilometres per hour. At 400km/h the air feels like butter and very difficult to persuade to move out of the way.
Most of us would have heard of Hyperloop or similar such systems. The concept is to travel at high speed (up to say 800km/h) through a tube which has had most of its air sucked out to create a vacuum. Hyperloop is normally portrayed in an above ground tube, but the concept would work equally well underground particularly on routes between congested cities. Over 20 years ago, scientists in Switzerland developed the Swiss Metro Concept. The concept was to utilise trains engineered to aircraft standard and run these in evacuated tunnels. The concept was to join each of the major cities in Switzerland and have commuting times measured in minutes rather than hours.
Using linear induction motors, the trains would effectively levitate and in the evacuated tubes would be virtually frictionless. As acceleration and deceleration rates would need to be limited for passenger comfort, the concept does need to be of sufficient length to be viable (i.e. you need a long enough length running at high speed to deliver the maximum benefit).
Freight Transport System
The conveyance of freight underground is an obvious and cost-effective solution to the problems of increasing congestion on our cities’ roads, increasing pollution of the atmosphere and the alarming rise in the fatality of cyclists. A high proportion of the goods transported on the roads around the world is conveyed on pallets. These pallets could easily be conveyed underground on autonomous smart pods powered with linear induction motors. Logistics centres on the outskirts of major conurbations would be used to facilitate just in time delivery via small diameter tunnels to underground distribution centres in the city centre. Tertiary delivery could be via a secondary capsule system, or more likely on the surface using electric vehicles.
A variant of this system will be used to convey 20ft and 40ft shipping containers from busy ports. Many cities around the globe suffer from the same challenge. Ports were often established hundreds or even thousands of years ago, with cities then growing around the port. Moving goods from these city ports often creates conflict and congestion on the existing road network.
Existing technologies have been developed to solve these challenges and it is becoming increasingly clear that the business case for such facilities is extremely compelling. Couple this with the sustainability, environmental and safety benefits these systems will bring and you must conclude that it is a question of when - not if - these systems will be built.
The Way Forward
New machines, materials and applications will radically change how we think about investing in underground infrastructure. These big ideas however need to be promoted by strong and determined champions who can win the confidence of investors, the public and politicians. I am sure that if visionary engineers such as Isambard Kingdom Brunel were alive today, we would already be benefitting from this revolution.