Gadgets will keep Seattle buildings safe during tunnel dig

SEATTLE -- Workers are getting ready to dig a massive tunnel underneath downtown Seattle as part of the Alaskan Way replacement project, and transportation officials hope some new high-tech gadgets will keep the city's historic buildings from being damaged.

Crews won't start digging the new tunnel for a few months, but Washington State Department of Transportation officials are already installing high-tech measuring devices on dozens of downtown businesses. The gadgets are part of a $20 million plan to protect the buildings while the tunnel is being dug.

When the enormous tunnel boring machine moves underneath the city, it will rattle the ground and buildings as it goes by, and that could create dangerous sinkholes.

That's what WSDOT officials hope to avoid, and that's why workers are already drilling a 200-foot-deep hole on First Avenue to install sensitive measuring devices to guard against giant unintended gaps underneath the buildings.

"We want to detect those early so we can deal with them at the point of source down deep before it has any chance of doing any damage -- architectural or cosmetic damage -- to the buildings," said Matt Preedy, the tunnel project's deputy administrator.

The devices being installed now will twirl every few seconds, aiming their lasers at hundreds of tiny reflectors that are precision-mounted on 200 buildings. The lasers will be able to detect if a building moves even an inch as the boring machine moves underneath.

What workers want to avoid is what happened when a tunnel was dug on Beacon Hill. That project damaged some buildings and caused headaches for homeowners, who were later compensated millions of dollars by the contractor.