Crews building the SR 99 tunnel in Seattle reach another milestone on Dec. 13 as they installed the 1,000th ring. The ring was installed 170 ft beneath Belltown as the miners continue their push toward the north portal. Tunnel boring is now 70 percent complete.
“We’re in a really good rhythm,” said Cody Heck, who builds rings for contractor Seattle Tunnel Partners. “I think my first ring that I built here was about an hour and a half. Now it’s down to about 40 minutes.”
With Bertha’s cutterhead approaching the ground beneath Third Avenue and Blanchard Street, tunnel boring is now 70 percent complete.
Meanwhile, other crews are making headway. A separate crew is hard at work behind the tunneling machine, building the double-deck highway that will carry traffic when the tunnel opens. Construction of the highway occurs in 54-ft sections.
Building the highway in this fashion allows concrete the time it needs to strengthen before additional components of the highway are added at a given section. It also allows workers to spread out and complete the portion they’re working on more quickly than would be possible if all crews were focused on the same area at the same time.
Crews are also nearing completion on what will ultimately be the most recognizable features of the SR 99 tunnel: the operations buildings at each portal with their bright yellow ventilation stacks.
The stacks are central to the tunnel’s ventilation system, which will be capable of removing 1.4 million cubic feet of air per minute should it be necessary. In addition to ventilation, the buildings will house operating systems, including safety, lighting and communications. They’ll also provide space and access for the very thing that inspired the colorful stacks – WSDOT’s yellow maintenance vehicles.
Both buildings will be mostly complete by next year, although a portion of the north operations building will be completed after the tunneling machine is removed from the ground. Crews have installed the stacks and main ventilation fans, as well as all exterior glass, in both buildings. The focus now is on completing the remaining interior work.
Permanent power was recently connected to the north operations building, which is located at the corner of Harrison Street and Sixth Avenue North. The building’s interior, as well as the plaza that’s taking shape outside, are now lit up at night.
The south operations building, which is located on the south side of South King Street, will be connected to the electrical grid in 2017.
Both buildings were designed to be beacons of light rather than blocks of cold concrete. The ventilation rooms of both operations buildings will stay lit throughout the night, acting as luminous bookends to the bored tunnel.
Tunnel breakthrough is expected to occur in 2017.