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Caltrans Blasts Old Bay Bridge Pier

Tuesday, November 17, 2015

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The much-anticipated implosion of the old Bay Bridge Pier E3 finally occurred Saturday morning (Nov. 14) in San Francisco, though onlookers were likely disappointed by the spectacle.

In just six seconds, 60,000 pounds of dynamite brought down the 20-million-ton concrete support, which lay entirely beneath the water’s surface.

Many viewers on hand expected to see the steel spans demolished, according to Wired magazine, but the only objects on the water’s surface were two barges on either side of the 80-by-140-foot pier, and the wood-and-steel protective covering that topped it to contain dust.

All that was visible during the event were spouts of water shooting up about 100 feet in the air, SFGate reported, and remnants from the protective covering afterwards.

Still, the blast registered as a magnitude-2.2 earthquake recorded by the U.S. Geological Survey, Contra Costa Times reported.

"Almost certainly what was recorded as an earthquake was the explosion itself," said Rufus Catchings, a USGS research geophysicist.  

Coming to Fruition

Earlier this summer, Caltrans applied for revised blast permits to remove this largest of the marine foundations, at 268-feet tall and sitting 50 feet below the surface of the bay.

Although Caltrans had received explosive permits 15 years earlier, at the start of the new San Francisco-Oakland Bay Bridge project, it now wanted to take advantage of advances in technology that would improve and speed the process, minimize effects on local marine wildlife, and meet regulations.

Rather than large explosives, more than 600 small controlled charges were set in the concrete and detonated simultaneously with the aim to collapse the rubble into what remains of the base of the structure beneath the mud line.

The demolition process also made use of an "air curtain" of bubbles to contain the explosion and inhibit the shockwave. A series of hoses, fed from the barges, blew compressed air through holes drilled in underwater pipes located around the pier to create the bubble screen.

Still, environmental groups expressed concern about how effective the air curtain would be and whether the charges would still disseminate debris into the surrounding water, affecting water quality, or emit shockwaves harming wildlife.

According to Plan

According to officials, the $20 million demolition went as expected, although it will still be several weeks before they can be certain whether the implosion felled the structure as required or had any impact on water quality and wildlife.

“As far as we know, everything went according to plan,” Leah Robinson-Leach, a Caltrans spokeswoman, told SFGate. “We can't know everything at this point.

“It could take days or weeks to survey the environmental ramifications on air quality, water quality and animals. We want to create the best methodology moving forward.”

If no unanticipated impacts are found, Caltrans plans to use this demolition method on the remaining 21 pier structures, at a total cost of $190 million.

The six-second blast achieved what would otherwise have taken four years and $100 million more to do by a mechanical process, Robinson-Leach told NBC’s Bay Area affiliate.

In the coming weeks Caltrans will make information available, such as 3D imaging of the bay floor showing the effectiveness of the implosion and any stray debris, the effect on fish and wildlife, and the composition of the dust cloud created by the implosion.

Environmental Impact

During the planning process, November was targeted as the ideal blast date, as experts determined this was a period when the least wildlife would be in the area, minimizing the impact on the environment.

Many bay species—including nesting birds, salmon and herring—are not present in November, Caltrans says.

Although the air curtain was expected to reduce the blast wave by about 80 percent, Caltrans officials did concede that as many as 1,775 endangered longfin smelt (about 1.3 percent of the remaining population, reports say), and possibly other fish, could be killed as a result of the event.

Still, this demolition method is believed to cause less environmental damage than the more time-intensive mechanical process would.

Controls were in place to keep two bird species, the endangered least tern and the protected brown pelican, and other large animals out of the blast area as well, using monitors and air horns to spook them from the site.

"In the coming weeks, we’ll be exhaustively collecting extensive data and determining the effects the implosion had on the environment and fish nearby," Maroney told NBC. "We don’t know exactly what it looks like down there, not yet."

Inadequate Packaging Led to Delay

Although everything went as planned Saturday, the demolition was pushed back one week from its original target date after Caltrans officials announced its inspectors were not satisfied with how some of the explosives were packaged, according to SFGate. Specifically, the cardboard-like wrapping was determined to be too thin.

Brian Maroney, chief bridge engineer for the Caltrans Toll Bridge Program, said the packaging material holding hundreds of dynamite charges was not strong enough and could fall apart, possibly preventing the explosion from being powerful enough to destroy the almost 8-decade-old pier.

"This is our process at work," Maroney said in a news conference, NBC Bay Area reported.

"Safety is the first priority. We commend the contractor for their diligent and extensive verification of the product they received, and for swiftly notifying us of the desire to reschedule.

“Safely and responsibly executing the implosion within the month of November remains our main objective."

   

Tagged categories: Asia Pacific; Bridge Piles; Bridges; Demolition; EMEA (Europe, Middle East and Africa); Environmental Control; Environmental Protection; Latin America; North America; Quality Control

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