It was supposed to fall, just not in that direction and not all at once.
A large section of the old Nalley Valley viaduct unexpectedly toppled onto South Tacoma Way on Friday afternoon as demolition crews chipped away at it from below.
No one was hurt in the accident, which happened about 1:30 p.m., but the force of the impact crushed underground water and gas lines beneath the pavement near the intersection with South Sprague Avenue.
Water flooded several blocks of South Tacoma Way before utility crews shut off supply lines. Utility crews also shut down gas lines in the area.
The structure landed on a portion of the street that had been closed to accommodate the ongoing demolition project.
“That’s our standard practice in demolition,” said Kevin Dayton, administrator of the state Department of Transportation’s Olympic region. “We’d cut down the road to one lane in each direction for a margin of safety, which is standard practice whenever you’re chipping concrete.”
The old viaduct, which until last month carried eastbound traffic on state Route 16, is being demolished to make room for a new, wider viaduct. The old structure was supported by distinctive “tetrapod” supports, which branched out from a concrete base.
Demolition crews removed most of the roadway spanning the tetrapod supports over the past month, leaving the unusual structures standing alone.
On Friday, crews were using excavator hoes equipped with hammers to remove the last of the roadway at the top of the tetrapod when the structure suddenly broke at the base, Dayton said.
Demolition crews planned to work through the night Friday, trying to clear the roadway, said Claudia Bingham-Baker, a Transportation Department spokeswoman. South Tacoma Way could remain closed from South Pine Street to South Wilkeson Street through the weekend, she said.
Rob Carson: 253-597-8693