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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.

July 01, 2006 — CSO — The decision to be a professional brings both benefits and dues, with one of the latter being at least occasional attendance at an annual awards dinner. Thus it was that a few years ago Gary Brierley, a consulting civil engineer, found himself listening to a speech by "Mr. Civil Engineer of 20xx." The happy winner stood up, thanked everyone, and unrolled the story of his project, which had to do with designing a high-security facility for the government. First the speaker listed the specs: The facility had to be able to withstand a direct impact from a big tornado, or to shrug off a crashing airplane. The usual. Then the engineer began describing his solutions: concrete walls four feet thick; layers of reinforcing steel and so on.

Brierley by his own account began to feel a touch of fatigue. Brierley is a specialist in underground construction, and he could see that the civil engineer was boasting about spending tens of millions of client dollars just to replicate on the surface everything that was already right there, literally under his feet.

This is an old and somewhat mystifying story for Brierley and other proponents of underground construction. In theory underground space hits almost every line on the CSO's wish list. It can be made nearly invisible from the surface, provides very tight access (and egress) control, and gives almost total insulation from surface turbulence, including fires, weather, riots and ordinance. Maintenance requirements are lower, which means fewer maintenance workers to pay. External support and insulation come free with the address, which means fewer worries about cracks and leaks. The ambient temperature is stable as a rock, pun intended.

Perhaps counterintuitively, underground space provides much better protection from earthquakes. Since a surface structure stands independently, with no external bracing, a wave passing through its foundation whips the structure back and forth, like yanking a rug from underfoot. And it gets worse: When earthquake waves hit the surface they interact with fields of objects that are complicated and heterogeneous, both geological and structural. These objects shatter the quake waves, bouncing them everywhere, twisting buildings back and forth in all directions. These are highly stressful experiences for any building, no matter how stoutly built. By contrast, underground structures live in a much quieter environment. A good analogy is the difference between experiencing a storm at sea under the water versus riding it out in a boat (on a cluttered surface). In 1999 professor Scott Kieffer of the Colorado School of Mines wrote a report comparing the damage wrought above and below ground by a major earthquake in Taiwan. There was no comparison. "The underground structures behaved so well," he says. "Worst case? Maybe it might leak a bit."