From Roman aqueducts to canal barge tunnels in the years leading up to the industrial revolution to the English Channel train tunnel constructed in the late 20th century, engineers have carved out spaces beneath the surface to benefit society.
Urban planners and civil engineers need to get in touch with their subterranean resources. Beneath their feet, waiting to be tapped, is an integral part of the solution to traffic and other urban congestion, according to advocates of subsurface development.
“From a public perspective, people generally don’t think a lot about tunnels,” said Colin Lawrence, tunnel practice leader of Hatch Mott MacDonald, the engineering firm headquartered in Iselin, N.J., with 76 offices in the United States and Canada. “Tunnels are less prominent than other types of infrastructure such as bridges and landmark buildings. Tunnel work can be fairly anonymous in the public eye, but it is essential to the future of society.”
A Long History
Actually, tunnels have been an essential part of the infrastructure for a very long time. From Roman aqueducts to canal barge tunnels in the years leading up to the industrial revolution to the English Channel train tunnel constructed in the late 20th century, engineers have carved out spaces beneath the surface to benefit society.
“Tunneling has so many applications,” said Lawrence. “Generally speaking, the ground does not know what you are placing inside a tunnel, or its final use, so many of the same challenges for tunneling exist across all types of tunnel.”
Mother Earth surely knows she is being probed. After all, the world’s longest underground rail route is not exactly minimally invasive: Gotthard Base Tunnel cuts through rock and soil in the Swiss Alps for 35 miles. Including all its auxiliary tunnels and shafts, nearly a hundred miles of tunneling was involved, requiring the removal of almost 28 million tons (25.4 million t) of rock.
Burrowing beneath an urbanscape also is doable, but such borings are more often done in other parts of the world, including Asia and Europe. In the United States, one of the highest profile urban tunneling undertakings was Boston’s Central Artery/Tunnel completed in 2007, which routed Interstate 93 underground. The so-called Big Dig cost about twice what was projected (the final bill was $15 billion, not including interest) and took an extra eight years to wrap up.
The project’s 3.5-mi.-long (5.6 km) Thomas P. O’Neill Jr. Tunnel constituted less than half the project’s total mileage, but it drew most of the attention across the country. When hundreds of salt and freshwater leaks subsequently began to drip onto pavement and a ceiling tile came unglued, fell and killed a motorist, a negative image was indelibly formed. Though Boston’s traffic congestion indeed was reduced by the Big Dig, the overall image of tunneling was not enhanced any.
More complex projects have been completed with less aggravation. For example, Hatch Mott MacDonald was involved in a 6-mi.-long (9.6 km) tunnel beneath Kuala Lumpur, Malaysia, that incorporates a double-decker traffic tunnel with an emergency flash flood runoff conduit on the lowest level. During major flooding, the entire tunnel — all three levels — becomes a storm water pipe. It was a $500 million project completed in just four years and, since 2007, has successfully diverted floodwater away from Kuala Lumpur’s downtown more than 40 times. Imagine, intentionally designing a highway tunnel to be flooded periodically.
Tunneling work accounts for 22 percent of Hatch Mott MacDonald’s business, according to Lawrence, but increasingly the work is inspecting and rehabilitating existing tunnels. He questions the ratio of tunnel repair work to full-scale upgrading.
“Is a state of good repair the only thing we should be considering? In the more vintage tunnels, shouldn’t we be upgrading to bring up to modern-day standards?”
Hatch Mott MacDonald performed the rehabilitation design work for the Hugh L. Carey Brooklyn Battery Tunnel in New York. The tunnel was flooded by Superstorm Sandy after the contract was let and the parameters of the current project were subsequently changed from rehabilitation to significant structural upgrade.
“It does beg a more general question of the industry: Why does it take a hurricane to do such a project in our major cities.”
The answer, of course, is money. After a disaster strikes, cobbling together the dollars to restore infrastructure that was lost always has public support, whereas preemptively spending money is a harder sell. Tunneling is an expensive undertaking, so taxpayers are particularly wary of such projects. Tolls can help offset costs, of course, but that can come across as double-dipping in tax-funded civil projects.
“Tolling is absolutely a help because of the extraordinary capital costs of projects,” said Neil Gray, government affairs director of the International Bridge, Tunnel, & Turnpike Association. The lobbyist said tolls are an acceptable method of recovering some capital costs from users of a facility. “A big part of the federal funding structure is terrified of talking about tax increases. Our argument is, OK, what about tolls?”
Gray noted that public demand for urban traffic tunnels is driven by perceived need. The need for a 9-year bridge-tunnel project in Japan was evident and generally supported. The Trans-Tokyo Bay Bridge-Tunnel, which was completed in 1997 and incorporated a bridge 2.5 mi. (4 km) long and a tunnel more than 5.6 mi. (9 km) long, cost $11 billion dollars. The kicker is that the tunnel-bridge created a way to drive from one side of the bay to the other in about 15 minutes instead of driving around for more than 62 mi. (100 km) through urban traffic including in downtown Tokyo.
Lawrence suggests that talk of tunneling costs is misleading.
“It is not a fair criticism that things are more expensive,” he said. “Planning for mega projects like tunnels is expensive. It really takes a lot of planning. You can’t do it overnight or in a few years. It can take decades because of the scale of a project and because the investment required is significant. So maybe a tunnel’s extra costs are a symptom of the planning and approval process, rather than of a tunnel itself. ”
He noted that new surface transportation projects that expand traffic capacity in urban settings can mean knocking down buildings and otherwise reconstituting life at street level.
“Moving underground, you can expand capacity with minimal disruption at the surface. I would respectfully submit that you have more real estate underground than you do on the surface in major cities. But it does require vertical planning.”
He added: “Whatever infrastructure you are contemplating, it has to be in harmony with the surroundings and that goes back to integrated transportation solutions. Major cities around the world have evolved with an integrated transportation network that encompasses tunnels for various transportation needs, rail and highway, but also incorporates surface transportation systems. An integrated transportation concept is the answer.”
Wanted: More Tunnels
Dr. Priscilla Nelson, who chairs the mining engineering department at the Colorado School of Mines, holds a holistic view of urban underground projects. She advocates full utilization of underground urban spaces for both traffic and public spaces.
“Urban planners in the future are going to have to go down even as they go up,” she said. “Urban sprawl is an inefficient way to deliver services. So we have to think totally anew and that means not just doing one tunnel project at a time, a sewer or a highway. We have to start thinking about the underground space for a city as a part of its natural resources.”
The engineering professor mentioned Texas cities Dallas, Austin, and San Antonio as urban areas with favorable underlying conditions for subterranean work. “New York has extremely good rock. In fact, where you see skyscrapers, there probably is pretty good rock. A lot of our cities have good foundations for underground work.”
Unfortunately, urban officials are not exactly rushing to exploit their sub-surface potential.
“In Austin, they are evaluating things. More should be done in Washington. In Boston, the tunnel project wasn’t a completely integrated thing,” Nelson observeed, adding that in some West Coast cities, officials have opted to relocate traffic arteries underground after earthquake damage. She touches on Lawrence’s comment about post-crisis funding: “If a city is prepared with plans, when a disaster hits, it is an opportunity to make things better.”
Nelson is a longtime consultant to the underground construction industry in the United States and Mexico and in conversation mixes academic observations with engineering pragmatism. She admitted to “being a little jaded about equipment.” She blames the larger and larger diameter boring machines for making the costs of a tunnel go up “like crazy” and for extending tunneling into more marginal and problematic conditions.
The removal of risk is one of the selling points of the huge boring machines, she said, yet she believes reliance on machinery to that end is counterproductive.
“One of the things people have been trying to do is shed risk of underground work so machines are being produced to remove risk. I think we need to go back and see what we can do to manage the risk, rather than remove it. Engineers need to change their attitude about risk. We need to better understand geological risk and regain our equilibrium about it and then costs of tunneling will decrease.”
Colin Lawrence sees a similar shift in operating philosophy.
“There are a lot of clever people designing boring machines. Hand in hand with the machines, there is innovation in such things as how to tunnel in soft ground conditions. There is continual improvement and innovation in the industry, including in safety. I don’t know what the acceptable death rate was a hundred years ago, for instance, but there has been a significant improvement in the safety culture. The acceptable rate today is, I would say, zero.”
Nelson actually sees an older method of tunneling regaining prominence.
“Blasting is going to come back into the urban environment in a fairly big way once we figure out how to handle the vibrations that cause damage,” she said. “We can do it better so it can be allowed to create large spaces, not just tunnels.”
To move ahead with urban tunneling, Nelson said engineers must have fuller understanding of their environment, including such fundamental concepts as how to better manage groundwater to reduce its deteriorating effect. She believes geological conditions are not fully and generally grasped by a current generation of engineers. For that, she blames curricula deficiencies.
She noted that an engineering bachelor degree in the 1950s required 208 credit hours. The required number of hours fell to 150 in the 1960s and now is under 140 hours and still falling. Geological study is among the reduced emphases.
“We have a problem here,” she said. “One of the responses to it has been to consider a master degree the first professional degree. We have to partner with industry to create a viable master degree where students can go and get the extra skills they need.”
Clearly, channeling traffic underground in urban settings and otherwise exploiting a city’s subterranean resources has roadblocks to get around, among them … cost, political will, and engineering know-how. But advocates argue that the advantages of digging into the ground warrant the effort of doing so. They argue that cars moving underground are protected from weather events, for example, and engine emissions can be captured rather than being released untreated into the air. The future composition and lifespan of materials — concrete, for example — may be enhanced as the materials are re-formulated for underground use.
From his seat at Hatch Mott MacDonald, Lawrence sees continued lengthening if tunnels. He believes 20-mi. (32 km) highway tunnels are practical today, and that engineers in time will tunnel farther for roadbeds. As they grow longer, Lawrence believes aesthetic engineering can overcome the human need to occasionally see the sky.
“Tunnels are only claustrophobic if you make the tunnels appear claustrophobic. There is much that can be done to address this.”
Professor Nelson said if city officials will conduct a fresh examination of their metro areas — including underground — they can provide better stewardship of city resources and a more livable urban experience.
“Cities someday may enter into long-time contracts with mining organizations to create space in different ways and depths. Highways are only one part of it. If we are to have more underground space, it has to be thought about better.
“Today we have too many civil engineers that are not thinking systemically,” she said, “urban planners that don’t even think about what’s underground, architects that don’t know a thing about underground. We obviously have some work to do. Maybe there’s a new profession in there somewhere.”