Welcome to a completed four full months of Bertha, North America’s largest tunnel-boring machine and the device clearing a tunnel under downtown Seattle for a new State Route 99, in idle mode.
With bearing seal rings damaged—and likely the main bearing too—crews from Seattle Tunnel Partners are still finalizing a plan to dig a 120-ft-deep pit in front of the machine to access Bertha for the needed fixes.
Even without an official plan for the repairs, the Washington State Dept. of Transportation did say crews are close to getting going on the repair pit. Instead of entering the already bored 1,000 or so feet of tunnel and disassembling Bertha from the backside to get to the main bearing near the front of the machine, crews will dig a 120-ft-deep circular pit in front of Bertha, 60 ft to the top of Bertha and another 60 ft to the bottom of the machine.
Once the pit below the surface between Jackson and Main streets in downtown Seattle is ready, the machine will then tunnel forward into the pit so crews can partially disassemble it and make repairs to the seal system and main bearing.
Before anyone could start digging, crews were required to dig 60 exploratory holes near the tunneling machine’s current location with project archaeologists on hand to determine if the soil had any archaeological importance. The holes 4 in. in diameter and between 20 and 40 ft deep dipped into historical fill material—the soil below 60 ft predates human settlement—and was required because the repair pit wasn’t part of the original boring plan.
Once inside the repair pit, crews will remove the cutterhead to gain access to the seal rings.
Every day this project puts Seattle Tunnel Partners behind a planned opening date of Jan. 2, 2016, will cost them even more money. While WSDOT says scheduling and budget impacts of the stoppage won’t be known until later, any day beyond Jan. 2, 2016, the tunnel isn’t open—apart from an approved change order—will cost Seattle Tunnel Partners $50,000 per day. That figure jumps to $100,000 per day after Nov. 1, 2016, up to a maximum total of $75 million. Of course, before the December 2013 shutdown of Bertha, Seattle Tunnel Partners was gunning for a $100,000 per day bonus—with a maximum of $25 million earned—for every day the tunnel was open before Nov. 1, 2016.
We don’t even know when Bertha will start tunneling again, but the repair pit is the next step in the process.
Tim Newcomb is Engineering News-Record’s Pacific Northwest contributor. He also writes for Popular Mechanics, Sports Illustrated and more. You can follow him on Twitter at @tdnewcomb or visit his website here.