Saturday, November 21, 2009

ONGOING COVERAGE: KENDALL YARDS

Bridge cracks near blasts

Monroe Street span safe, city says, as Kendall Yards work continues

A number identifies a crack on a Monroe Street Bridge support. The concrete bridge reopened in 2005. The Spokesman-Review (JED CONKLIN The Spokesman-Review) • Video: Kendall Yards blast

Jonathan Brunt
Staff writer
September 22, 2007

City engineers raised concerns this week that minor cracks in an abutment in the Monroe Street Bridge may have been caused by explosives detonated during construction of the future Kendall Yards Boulevard.

Officials stress that the bridge remains safe and the cracks can be sealed without significant expense.

"There is a possibility that it might have happened during one of the blasts, but we don't know for sure," said Spokane's bridge engineer, Mark Serbousek.

Kendall Yards representatives, however, say readings indicate that vibrations from the explosions were too low to have created the damage. But they agreed to take extra seismic measurements during detonations, including one Friday morning.

"We're pretty confident that it's not attributable to the construction activity," said Kendall Yards Project Manager Tom Reese.

The concrete Monroe Street Bridge, which is represented on the city's seal, opened in 1911 and – after a 2 1/2 year, $17 million reconstruction project – reopened in 2005. The abutment with the cracks was built in the recent work and is on the far north side of the bridge.

City engineers were informed about the blasts early this week by Avista employees concerned the explosions could have damaged the nearby Monroe Street Dam. Avista spokesman Hugh Imhof said the company found no damage on the dam after a thorough examination.

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The cracks that were found on the bridge were not recorded in its last inspection, which was completed in 2006, said Serbousek, who also is the city's street director.

"My inspector does a pretty thorough job, and it's not noted on his inspection reports," Serbousek said.

Kendall Yards and Avista are constructing a trench for utility lines that will be under the future main avenue of the 78-acre commercial and residential development. Detonations are expected to continue for several weeks as workers attempt to break up rock for the trench.

Lewiston firm Cromer Drilling & Blasting was hired to complete the job and received a blast permit from the city on Sept. 4, which allows it to detonate between Sept. 5 and Dec. 31.

Public Works Director Dave Mandyke said city engineers are examining data from three previous explosions and one from Friday. They decided to request extra testing during Friday's test, and in future examinations, and not halt work because there is no conclusive evidence that the cracks were related, he added.

"It's basically an ongoing study," Mandyke said. "What we're seeing is maintenance items, hairline cracks, these types of things."

Serbousek said it's important to keep a close eye on future detonations to protect the taxpayers' investment in the new bridge.

Reese said blast officials surveyed the bridge, dam, nearby commercial buildings and other structures before making any detonations.

He said vibrations measured on the bridge from Friday's blast measured 0.04 inches per second.

Mark Aguiar, state explosives inspector for Eastern Washington, said state law requires that vibrations from explosives experienced by inhabited structures be limited to 2 inches per second.

"That's a very, very, very low reading," he said, referring to the 0.04 number.

The earlier detonations were measured, but it was unclear how the 0.04 reading from Friday compares to the three previous ones completed before the city asked for extra seismographs on site. An attempt to reach a consultant hired by Kendall Yards to examine the blast data was unsuccessful late Friday afternoon.

The next detonation is scheduled for Monday morning.