Steam vaults blamed for collapse of Forsyth Street

Atlanta officials now know what caused part of a downtown Atlanta street to collapse, but the mystery remains about two other collapses in the same area.

Atlanta watershed management spokeswoman Janet Ward said Thursday that three or four large steam vaults recently collapsed under Forsyth Street just south of Alabama Street, causing part of the pavement to give way.

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Chandler Brown /CMBrown@ajc.com

City officials say they’re not sure why part of the upper plaza of Underground Atlanta gave way.

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The vaults are about 15 feet wide and 14 feet below the street, Ward said. They probably “date to the ’20s, when buildings were heated with steam,” Ward said in an e-mail. The departments of watershed management and public works began backfilling the vaults with dirt and gravel on Thursday, Ward said. Once that’s complete, they will repave the street.

Ward said it was too early to tell how long the work would take or how much it would cost.

“This is a very unique situation,” she said.

Officials still aren’t sure what caused a Forsyth Street sidewalk to buckle, nor do they know why part of Underground Atlanta’s upper plaza collapsed just after midnight on New Year’s Day.

Engineers were scheduled to visit Underground Thursday, but their findings were not immediately known.

“It’s still under investigation,” said Valerie Bell-Smith, a spokeswoman for the city’s public works department.

Underground is owned by the city but managed privately.

“We’re kind of in a holding pattern, waiting for the city engineers to determine how to proceed,” Underground Atlanta spokeswoman Tara Murphy said Thursday.

All three areas remained cordoned off Thursday evening.