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Caltrans Seeks OK for Blast Demo

Thursday, August 20, 2015

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The old Bay Bridge is coming down. As much of the concrete and steel structure are being dismantled piece by piece, Caltrans is in the process of securing permits to demolish the main supporting pier, E3, with explosives.

Now that the cantilever truss has been removed on the 77-year-old East Span in Phase One of the project, crews are at work on the five 504-foot and 14 288-foot truss spans of the structure, Phase Two.

Caltrans

Caltrans is updating its explosives permits to use a new controlled charges plan to demolish the largest support pier in the old Bay Bridge structure.

Phase Three takes place at the waterline on the piers, pilings, and foundations supporting the span. Contractors will remove the underwater support foundations, demo the piers and pilings to the waterline, and then extract foundations down to the mud line, Caltrans reports.

Pier E3 is the largest of the marine foundations, at 268-feet tall and sitting 50 feet below the surface of the bay.

Air Curtains & Controlled Charges

In a video posted by Caltrans, spokesperson Leah Robinson-Leach indicated that explosives permits were originally secured 15 years, at the start of the new San Francisco-Oakland Bay Bridge project.

However, improvements in explosives technology since then have led them to present permit amendments to update the agencies on how controlled charges would now be carried out, minimize effects on local marine wildlife, and meet regulations.

Using hundreds of small controlled charges behind a curtain of air would enable Caltrans to bring down the bridge in just six seconds and control the dispersion of rubble.

According to Bay City News Service, federal agencies—including the U.S. Department of Commerce and the National Oceanic and Atmospheric Administration—are taking public comment on the planned implosion until Monday (Aug. 24).

If approved, demolition of Pier E3 would take place in November. This target was determined by experts as a period when the least wildlife would be in the area, minimizing the impact on the environment.

Inside Bay Area News described the demolition process as using an "air curtain" of pipes that would blow compressed air through the water around the pier. More than 600 small explosives would be set in the concrete and detonated simultaneously, collapsing the rubble within the air curtain, they reported.

In the Caltrans video, Brian Maroney, Toll Bridge Project chief engineer, indicated the use of hundreds of small controlled charges, as opposed to large explosives, would enable them to take down the pier in just six seconds.

Allowing for the cleanup time needed, he expressed that this method gets them in and out of the area quickly, making it the best option for the environment, the schedule and the cost of the project.

And while traditional mechanical removal involving a coffer dam was also considered, this was dismissed for not being as efficient or cost-effective.

Despite the Caltrans research and planning, Baykeeper, an advocacy organization for the health of the San Francisco Bay, still harbors concerns that the charges could disseminate debris into the surrounding water, affecting water quality.

"We're not convinced that the air curtain is going to contain the concrete," he told Inside Bay Area News.

Baykeeper is working with Caltrans to monitor and ease environmental impact as a similar demolition process may be used to bring down the other bridge support piers.

Project Scope

According to the San Francisco-Oakland Bay Bridge Seismic Safety Projects site, the demolition project is scheduled to take place over three to five years. When complete, more than 58,000 tons of steel and 245,000 tons of concrete will have been removed.

Caltrans

Demolition of Pier E3 is Phase Three of a project expected to take place over three to five years.

Engineers are using a 3-D finite element computer program model, based on structural analysis and historical records showing the distribution of forces, to determine how best to remove high-tension pieces.

Additionally, the team keeps an eye on the state of the span through a system of 90 retroreflector prism targets installed at key locations on the bridge. As steel elements are removed, the updated target locations are determined and entered into a computer system. This data is then compared against the predicted locations in the finite element model software.

The Bay Bridge website indicates extensive monitoring and mitigation efforts will continue as environmental teams works with demolition crews to ensure safety throughout the demolition project.

   

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

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