Archaeological tests begin at Bertha site

WSDOT says the testing shouldn't cause any delays with the boring machine's repair schedule.
WSDOT says the testing shouldn't cause any delays with the boring machine's repair schedule.

Even though Bertha's at a standstill, there's new boring going on at the Highway 99 Tunnel site. Washington State Department of Transportation crews are drilling archaeological test holes near South Main Street. 

The project's lead contractor, Seattle Tunnel Partners plans to dig an 11-story-deep shaft in the area. The test holes will help archaeologists determine if the shaft will cut through soil that contains artifacts or other cultural remnants. WSDOT will drill a total of 60 test holes during the next week, a WSDOT archaeologist said on Thursday. Each hole will be approximately 4-inches in diameter and 20-40 feet deep. The soil in the area is a mixture of material; some was used to fill in wetlands during the mid-19th century.

Seattle Tunnel Partners will use the shaft to access Bertha, the 57.5-foot wide boring machine that was digging the tunnel and now needs repairs.

WSDOT said the archaeological tests should not delay those repairs. And there are no current plans for archaeological work beyond the test holes. The tests are required under Federal Highway Administration cultural preservation guidelines. WSDOT archaeologists are in contact with the Muckleshoot, Tulalip, Suquamish and Snoqualmie tribes and have also reached out to the Duwamish tribe. But the soil tests will look for anything of archaelogical significance, not only native artifacts.

Transportation Department archaeologist Steve Archer said that staff experts would be checking the age of the soil samples and looking for relics. Some of the soil, he said, could date back 10,000 years. Previous tests at other parts of the tunnel site have unearthed items such as prehistoric rope.

Because the repair shaft extends 60 feet above the originally planned tunnel route, it will involve excavating soil that WSDOT did not check during earlier archaeological surveys.

The agency also said Thursday that Seattle Tunnel Partners has nearly finalized a plan for digging the repair shaft.

In February, the contractor had discussed a rectangular-shaped shaft that would be roughly 80-feet wide and would extend 36, 42, or 65 feet in front of the machine. That concept has been altered slightly. Working with Hitachi Zosen, Bertha's manufacturer, the contractor has developed plans for a circular-shaped shaft. 

Crosscut archive image.
Who knows what they'll find down there. Drilling equipment near the future site of Bertha's repair shaft.
Photo: Bill Lucia 

Matt Preedy, WSDOT's Deputy Program Administrator for the Alaskan Way Viaduct Project, said he did not know the exact dimensions, but he did say the hole would be big enough to remove the machine's cutter-head and place it above ground. Concrete will line the interior of the shaft. Once it's built, operators will drive Bertha forward slightly, busting through the shaft's southern perimeter.

A set of seals that protects Bertha's approximately 35-foot diameter main bearing is damaged and needs to be replaced. The contractor has not determined whether the bearing itself was damaged by grit or water. Preedy said the earliest that Hitachi Zosen would provide a final repair plan for the machine would be the end of this month.

Enjoyed this story? You might also like: "Could Bertha boondoggle be a local history boon?" by Knute Berger.


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