There are still “thousands of guesses” of what is holding Bertha, the tunnel-drilling machine, from moving forward under downtown Seattle, according to state officials.
The design-build contractor for the tunnel project is lowering groundwater to get a closer look at what’s blocking Bertha.
The initial inspection is scheduled to be completed next week.
Engineers are skeptical that it’s a locomotive or any other kind of man-made object because the tunnel boring machine is already deep beneath the fill dirt that was used to build the Seattle waterfront.
Engineers stopped work proactively last Saturday after the machine felt resistance because of the obstruction. On Monday, a project spokeswoman told KIRO 7 Bertha encountered the obstruction on Friday.
The best case is that something is stuck the machinery behind the cutter head, officials said. Something in front of the cutter head would be much more difficult.
Contractor Seattle Tunnel Partners is proceeding with two plans simultaneously to free the machine if that is the case. One is to send divers working under high pressure into the tunnel to break up the obstruction. The other is to bore in from atop the machine and create a concrete chamber with regular atmospheric pressure that workers can be used to remove a larger obstruction Project Manager Chris Dixon said.
Constructing the concrete chamber from the surface could take 5 weeks or more.
Bertha is about a 1,000 feet into the 1.7-mile dig. The first section of the dig goes through fill soil that was part of Elliott Bay in Seattle's early days.
State officials are unsure how long Bertha will be stopped.
The machine began digging on July 30, but a Longshore union labor dispute delayed digging from August 20 to September 23.
The tunnel project is part of the state's overall $3.1 billion plan to replace the Alaskan Way Viaduct, the double deck highway along the downtown Seattle waterfront.
The $80 million machine is working on a nearly 2-mile tunnel expected to take 14 months. The 58-foot diameter tunnel is scheduled to open in late 2015.