Tunneling and underground construction—likely first performed by prehistoric humans who sought to make their cave homes larger—has a long and varied history.
In time, all major ancient civilizations developed their own methods of building beneath the surface. The Babylonians used tunnels extensively for irrigation. Ancient Egyptians developed copper saws and hollow reed drills used to excavate temple rooms in rock cliffs; similar constructions out of solid rock have also been found dating back to ancient times in Ethiopia and India.
The ancient Greeks and Romans also used tunnels to drain marshes and for aqueducts. Possibly the largest such construction from ancient times is the Pausilippo tunnel, built between Naples and Pozzuoli in 36 BC, measuring 4,800 feet long, 30 feet high and 25 feet across—especially impressive, given it was essentially dug out by hand.
Gunpowder was first used to blast tunnels out of rock in France in 1681. Dynamite came into use in the mid-19th century, alongside the development of drills powered by steam and compressed air, used to create holes for explosive charges. Inventors also developed shield techniques, where an enclosure supporting the earth above moves with workers as they dig underground—this was used to construct two tunnels under the Thames River in London between 1820 and 1865.
Now, much tunneling for utilities and transportation is accomplished using self-contained tunnel boring machines, which can be designed to dig through anything between sand and hard rock. They can be used to dig tunnels as small in diameter as one meter, but the largest TBM, Bertha, has a diameter of nearly 60 feet and was built for the Alaskan Way Viaduct replacement tunnel project in Seattle.
Along the way, the mining industry has contributed to and benefited from advances in underground construction technology.
Colorado School of Mines, established in 1874, has been named the top mineral and mining engineering school in the world in the QS World University Rankings for four years running. This pedigree in mining and geological engineering and the earth sciences in general, as well as Mines’ highly ranked civil engineering program (No. 40 among graduate programs in the country according to U.S. News & World Report), means the university was particularly well suited to launch the first and only underground construction and tunnel engineering graduate program in North America in 2012.
It’s no surprise that Mines alumni worked on that Alaskan Way Viaduct project; students in the program at the time even contributed to as part of their project design course. “They got to design components of the largest bored tunnel in the world,” says Civil and Environmental Engineering Professor Mike Mooney, who leads the graduate program in UCTE at Mines.
The Push Underground
These days, much of tunneling and underground construction is driven by increased urbanization. “Urban areas have less room but need more infrastructure—water, wastewater, stormwater, energy utilities, data centers,” says Mooney.
“Tunneling is one promising alternative for solving these problems and meeting the demands of our growing cities,” says Ryan O’Connell, a master’s student in underground construction and tunnel engineering at Mines.
Building underground not only helps meet the needs of crowded metropolitan areas—it can also do so sustainably. The book Underground Engineering for Sustainable Urban Development, produced the National Research Council and published in 2013 by The National Academies Press, outlines the contributions engineered underground space can make to sustainable development and outlines what can be done to maximize those contributions.
Well-planned underground infrastructure can positively influence land use and development decisions and can reduce vehicle use and associated impacts. High-density urban centers may depend on centralized services but can capitalize on centralization to increase sustainability. Underground transportation infrastructure (e.g., urban roads and highways, public transit subways, grade-separated and underground freight railroads, high speed rail, and pedestrian rights of way) can address multiple growth-related challenges in urban areas (e.g., congestion, urban sprawl) if infrastructure elements are optimally designed and located. Well-planned and operated underground infrastructure can, in many cases, improve quality of life and sustainability more so than can similar-purpose surface infrastructure.
Rapid transit is the focus of Elon Musk’s The Boring Company, inspired by Los Angeles traffic and the limitations of current surface transportation networks. According to the company’s website:
To solve the problem of soul-destroying traffic, roads must go 3D, which means either flying cars or tunnels. Unlike flying cars, tunnels are weatherproof, out of sight and won’t fall on your head. A large network of tunnels many levels deep would help alleviate congestion in any city, no matter how large it grew (just keep adding levels). The key to making this work is increasing tunneling speed and dropping costs by a factor of 10 or more – this is the goal of The Boring Company.
Musk envisions more than just underground roads—he and other companies such as Tesla and Virgin are working toward creating public transportation systems called hyperloops that can travel as fast as hundreds of miles an hour. (Mines students have taken part in his SpaceX Hyperloop Pod challenge.) The concept calls for passengers and freight to be propelled in pods through sealed vacuum tubes, free of air resistance or friction.
As technologies improve, tunneling and underground projects become even more ambitious: ever-longer undersea tunnels, subsurface storage of petroleum, highway tunnels that reduce pollution by treating emissions collected by their ventilation systems—all the way to tunneling on the Moon.
All this is in addition to existing underground infrastructure that must be maintained and improved as they age and as population centers continue to grow. A quick look through any tunneling industry publication shows the breadth of projects underway all over the world: new metro lines in São Paulo, Moscow, Copenhagen; London’s Crossrail; hydropower projects in Laos—safe to say, the industry is far from reaching the bottom.