Big Bertha’s delays have pushed back the opening of the tunnel it’s digging by 20 months…so far

The pit being dug to access and repair Big Bertha will reach 120 feet below the surface. Credit: Washington State Department of TransportationThe pit being dug to access and repair Big Bertha will reach 120 feet below the surface. Credit: Washington State Department of Transportation

Seattle’s new State Route 99 tunnel is officially 20 months behind schedule, and it’s all Bertha’s fault.

The Associated Press reports Washington State Department of Transportation officials are now saying that the new tunnel being dug beneath Seattle by Big Bertha, the largest tunnel-boring machine in the world, won’t open until August 2017. And they can’t guarantee that date won’t change again in the future.

The huge delay is due to a long list of setbacks, the latest of which was a stop in excavation for a 12-story repair pit being dug in front of Bertha after officials started to suspect groundwater pumping at the site was the cause of major soil sinkage in the area.

According to the AP report, excavation has resumed at the site after a brief investigation found that while the ground settlement—which was as much as 1-1/4 inches in some places—while “greater and farther reaching than anticipated,” has remained stable since late November.

Bertha went down from overheating in late January, one-tenth of the way through digging the 1.7-mile State Route 99 tunnel which will carry a double-deck highway and replace the SR 99 Alaskan Way Viaduct. Water and sand clogged her cutterhead openings and penetrated seven rubber seals meant to protect the main bearing. In repairing the machine, crews will install 216 steel ribs and plates that will add 86 tons of reinforcement to the 7,000-ton machine’s drive block and cutter drive.

Seattle Tunnel Partners, the contractor leading the project, expects the machine to be operational and tunneling again by April of next year.

The new completion date is even a full year later than the estimated date given when the machine first went down. The original completion date, before all the setbacks, was November 2016.

Crews are more than halfway through digging a 120-foot-deep pit that will be used to access the machine for the needed repairs. Once the pit and its walls are fully built, crews will then pull Bertha’s 630-ton cutterhead, drive axle and bearing to the surface in order to replace the bearing and add steel reinforcements.