August 31, 2011

Irene exposed bridge's fatal flaw

State planned to fix Route 27 structure that collapsed into river

CARRABASSETT VALLEY -- The bridge that collapsed into the Carrabassett River during Tropical Storm Irene had been scheduled for repairs to help fix a design flaw that made it more likely to fail during severe storms.

click image to enlarge

BROKEN: Ted Clark, a project manager for Reed & Reed General Contractors, surveys the damage to the bridge next to the entrance of Sugarloaf Mountain Resort on Route 27 in Carrabassett Valley Tuesday afternoon. Reed & Reed is one of five contractors the state is considering for the reconstruction project. The bridge, which the state says had a design flaw, was one of two spans wiped out in Carrabassett Valley by floodwaters from Tropical Storm Irene on Sunday.

Staff photo by Michael G. Seamans

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Built in 1958, the bridge was slated to be repaired within the next 12 months because of the flaw in its support system, which only becomes a danger during flood conditions, according to John Buxton, bridge maintenance engineer for the Maine Department of Transportation.

It was one of the bridges on Route 27 that crumbled Sunday afternoon into raging, flooded waterways in Carrabassett Valley, the northern Franklin County town that was one of the hardest-hit in the state by Sunday's storm.

Buxton said Tuesday that he is trying to find out the specifics of the bridge's collapse during the extreme weather conditions.

The answers may help prevent future disasters because there are 129 other state-owned bridges statewide that have similar design flaws, which are mostly tied to pre-1960 design flaws in regard to soil erosion, he said.

A team of engineers and other scientists is looking into what caused the two bridges to collapse, but early signs point to storm waters overwhelming the structures, Buxton said.

He described it as localized flooding that would have caused a variety of bridges to collapse.

Buxton believes the water levels met guidelines for a 100-year flood, which refers to a system that rates storms based on how they compare to average annual rainfall. A National Weather Service spokesman confirmed reports that 8.5 inches likely fell where the bridges failed.

The other bridge that collapsed nearby on Route 27, falling into Brackett Brook, which feeds into the river, had been built to replace a smaller, less durable bridge. The DOT engineers felt the original model couldn't stand up to frequent flooding at the site, Buxton said.

Hundreds of employees of the state regulatory agency were monitoring road and bridge conditions throughout the state during the storm. They measured water levels all day to determine whether to shut down bridges, and many were shut down because of flooding, he said

One of the agency's crews measured the levels at the bridges in Carrabassett Valley just two hours before they both collapsed within minutes at about 4:30 p.m.

The river's water rose at least two feet during the two hours, going from levels three feet below those considered dangerous to spilling over the bridges, according to Buxton. He said the crew arrived back at the bridges just a short time after they collapsed.

Buxton said the two-hour time lapse was because the crew also had to check other bridges. Some 2,753 state-owned bridges were monitored during the storm, he said.

The 129 bridges flagged by the agency for the same flaw as the one that collapsed Sunday are stable for everyday use, and most are expected to have a life span of 75 to 100 years, said Buxton.

The flaw is that support beams become unstable because of soil erosion during severe storms. The regulatory agency manages the problem by increasing inspections and maintenance, he said.

Engineers are looking at installing temporary bridges and improving private dirt roads as temporary fixes so people can get around where the two bridges collapsed, with some traffic being detoured around nearby highways.

The long-term plan is to replace both bridges, according to an agency spokesman.

David Robinson -- 861-9287

drobinson@centralmaine.com

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