This time, the problem didn't originate with the tunnel boring machine itself. The issue that halted the operation was a listing barge hauling excavated soil out of Elliott Bay to a site near Port Ludlow.

From Mike Lindblom at the Times:

The barge, docked at Port of Seattle Terminal 46, began to list as it was loaded by Seattle Tunnel Partners (STP) workers. They released the barge from its mooring to prevent damage to Bertha’s conveyor equipment. Some dirt spilled into Elliott Bay, the Washington State Department of Transportation reported.

The barge drifted to the decrepit, state-owned Pier 48, then was pushed by tugboat back into place.

STP plans to remove dirt from the unbalanced barge and reload it onto a second barge, said state spokeswoman Laura Newborn.

And nobody knows how much this delays the digging. As of last week, Bertha had drilled at least 73 feet after two years of examinations and repairs.

UPDATE:

Seattle Tunnel Partners (STP) has divers assessing the damage, WSDOT reports. This is a serious operation; STP also has a "barge-mounted clamshell" (a clamshell looks like this) to scoop up dirt from the screwed-over barge to a different barge.

More from WSDOT:

STP anticipates resuming tunneling and disposal of excavated materials after a third barge returns to the site from unloading excavated material at CalPortland’s Mats Mats reclamation facility in Port Ludlow. They must also confirm that a barge can be safely staged at Terminal 46.

As of Tuesday morning, STP had mined more than 190 feet and installed 30 concrete tunnel rings since Bertha first moved forward in the pit on Dec. 22. This brings the total distance tunneled to 1,280 feet and a total of 188 concrete rings.