The aging Alaskan Way Viaduct has been settling for years, leading to cracks.
This year, for the first time, some of those cracks have been caused by the viaduct settling against the off-ramp at Seneca Street.
They're different structures that are supposed to be separated by an expansion joint.
"Now that viaduct has moved closer to Seneca, they've closed the gap and we have to re-establish that gap," said David Sowers, deputy administrator for the Alaskan Way Viaduct Replacement Program at the Washington State Department of Transportation.
The gap disappeared when the viaduct settled, increasing pressure and causing cracks discovered during a spring inspection.
State workers have already filled the cracks with epoxy.
"We have not seen any movement on those cracks since March," Sowers said.
The plan now is to prevent more cracking by restoring a 3-inch gap between the structures.
It will be one of several projects during the longest closure of State Route 99 in nearly three years.
On Friday, Aug. 22, SR 99 will close from the West Seattle Bridge to Valley Street in South Lake Union for the entire weekend.
On Monday, Aug. 25, the viaduct will reopen but SR 99 from the Battery Street Tunnel to Valley Street will stay closed until early Wednesday morning while crews remove a bridge over Broad Street.
"We want to get the message out to people to take alternative routes, change your commute times," Sowers said.