Jan. 7 update: crews begin drilling shafts in front of Bertha

Posted on Jan 7 2014 4:46 PM

Crews spent the weekend preparing the ground around Bertha, the SR 99 tunneling machine, for further investigation. They started by injecting a low-strength blend of cement and sand into voids that had developed in the ground in front of the machine. The voids were expected due to the recent removal of water and soil from the machine’s excavation chamber, which was necessary for crews to safely inspect it last week.

With all of the voids now filled, crews will be able to better assess the situation. Late this morning, they started drilling 5-foot-diameter shafts in front of Bertha. These shafts are being installed where earlier probing detected metal in front of the machine.

The plan is to further identify the limits of any metal in front of the machine and remove as much of the metal as possible. Crews are also continuing to gather additional information about any other factors that might have contributed to the obstruction that stopped tunneling last month. The overall cause of the tunneling slowdown will not be known until the investigation is completed.

New photos
A lot of attention has been focused on the 8-inch-diameter steel pipe that was discovered during last week’s inspection, but other interesting objects have passed through the machine.

Here’s a shot of some boulders that made their way through Bertha’s conveyance system before her progress was slowed, as well as several pieces of metal that are believed to be part of the pipe.

A second photo shows a 57-foot-long section of pipe that’s now lying in the construction yard. This section of the pipe was pulled from the ground after it was struck by the machine in early December.

Previous updates

Jan. 3, 2014 update -- Progress made in search for tunnel blockage

Dec. 20, 2013 update -- We won't know more about Bertha's blockage until 2014

Dec. 13, 2013 update -- Tunnel crews lowering groundwater to get a closer look at what's blocking Bertha

Dec. 5, 2013 update -- Seattle Tunnel Partners: Almost the proud owners of the world's largest tunneling machine

Nov. 25, 2013 update -- Bertha has much to be thankful for as she nears South Jackson Street