Chemical "explosion" used on giant rock unearthed downtown

Most of the time, in downtown Seattle construction projects, crews dig up a mixture of glacial till and clay. It's your basic Northwest dirt.

But on Monday, where the southeast block at Fairview Avenue North and John Street is being excavated to build a retirement center, something quite large protruded from the ground.

It was a giant granite boulder, measuring about 12 feet by 8 feet and estimated at 20,000 to 25,000 pounds.

Jerry Peterson project manager for SCI Infrastructure, of Pacific, the contractor removing 60,000 cubic yards of dirt off the site, now had to decide what to with the big rock.

A granite boulder is not typically found in downtown dirt but closer to the mountains, he said.

Peterson knew that the giant rock couldn't be dealt with as it would have been in the old days. He had to go chemical high-tech.

"I imagine people typically in the old days inserted sticks of dynamite and then would shoot the rock," he said.

Not anymore, especially in a downtown area, he said.

There are regulations about using explosives; insurance costs are high; in some cases, contractors have to videotape nearby structures in case of complaints the explosion caused damage. There also is the underlying concern of any company handling explosives — that people with bad intentions might get hold of the materials.

So Peterson used a product manufactured in the Principality of Liechtenstein, a tiny landlocked state sandwiched between Austria and Switzerland.

Construction sites — with their huge machinery moving around all kinds of big stuff — seem to attract the attention of passers-by.

At this site, people watched as Chuck Jackson, part of the SCI crew, drilled about 35 4-foot-deep holes into the granite boulder. Some of the holes were filled with a product that was invented in 1988 by Bruno Meyerhans, a Liechtenstein chemist.

The product is called Betonamit, and it's advertised as "an explosionless explosive" that blows up rocks, boulders and concrete.

"It is a wonderful powdery mix," said Tim Brown, president of Windy Ridge, of Tamworth, N.H., the North American distributor for the product.

The genius of Betonamit, he said, is that all you do is add water and pour it into the drilled holes, and wait overnight.

"The key is that as it hardens, it cements itself to the drill hole, and then it begins expanding," Brown said. "If it didn't cement itself into the drill hole, it'd just puke out of it."

Some of the drill holes are not filled with the chemical, so as the rock begins breaking, it has somewhere to go.

That's all there is to it. Betonamit is caustic but nontoxic. Its hazardous component is lime.

On Thursday afternoon, a line of trucks hauled out the split-up chunks of granite, and trucks were again making 100 trips daily hauling the usual dark gray dirt.

Erik Lacitis: 206-464-2237 or elacitis@seattletimes.com