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Holes: Is Underground Construction the Answer to Security Problems?

Some vexing security and safety challenges have a simple solution: Move the buildings underground.

TBMs will probably not get much larger, but they will certainly get faster. Rock sensingâ¬using acoustics to give TBMs "headlights" so they can see and prepare for changes in ground conditionâ¬is becoming standard, as is remote control and unattended operation. Recent discoveries in materials science will allow much tougher cutter wheels, which means faster speeds through harder rock. New industry IT standards will allow machines to consult design and seismic databases on the fly. Under way are experiments such as equipping TBMs with lasers, since warmer rock shatters more efficiently. Today about 150 TBMs are working around the world at any one time, and that number may double over the next 10 years.

Meantime, drill and blast, now used mostly to hollow out caverns as opposed to tunneling, has picked up the pace impressively. Contemporary drills come stuffed with sensors that monitor their own vibrations and thermal behaviors. Since different kinds of rock make drills behave in different ways, these sensors allow the drill to tune itself to the material at hand, including controlling the explosives mix. This intelligence means the rigs can drive faster without damaging the ambient rock, historically the big downside of drill and blast. A modern drilling rig can create space almost as fast as a tunnel boring machine, with the advantage of requiring a lot less capital up front. The two technologies are competing to see which can lower costs faster.

Eventually the cultural barriers that so annoy Brierley will dissolve and underground space will pick up another driver: security. That day might arrive soon. An increasing number of disaster recovery services are marketing underground storage of both documents and backup servers as a feature. According to Mike Smith, proprietor of industry portal TunnelBuilder.com, weather security is Ârising in importance all around the world as a justification for underground highways.

For decades Boston was content to drink from a surface aqueduct (the Hultman Aqueduct). Anyone with the dollars to rent a backhoe for a few hours could have cut the water supply of the entire city, perhaps for several days (puncturing the system would probably have caused lots of ancillary damage). Recently the national culture changed, and this vulnerability became intolerable. As a result, the money was found to drive a tunnel through granite and quartz ground, which are about as unfavorable as ground gets. Smith thinks that eventually security will join rising real estate prices as one of the basic motives for going underground. At the very least this new application will draw in still more investment, driving costs down still further. In decades to come this trend might look less like a convenience and more like a migration.