Before a repair pit can be dug in front of the stranded Highway 99 tunnel machine, crews will probe the dirt for historic artifacts.

Sixty vertical holes are being drilled for a search that will take about a week, said Steve Archer, cultural-resources specialist for the Washington State Department of Transportation (WSDOT). The machine known as Bertha sits 48 feet deep near the waterfront at South Main Street.

After the soil surveillance is done, Seattle Tunnel Partners (STP) will build a 120-foot-deep vault, so that contractors can remove the disc-shaped cutterhead and fix Bertha’s damaged main bearing.

The archaeological test holes will be shallow, to check the area above the tunnel machine, before that area is disturbed by STP’s pit excavation. The actual tunnel path, which is between 48 and 105 feet deep is thought to be mostly glacial soil, generally below a level that woul ever have been inhabited.

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If the state archaeological review comes up empty, there ought to be zero delay to STP’s work.

Archer doesn’t necessarily expect to find objects within the 4-inch-wide probe holes.

But he said scientists will look at soil layers for clues as to where human activity occurred — anytime between 10,000 years ago and 1950.

The WSDOT would gather any Native American objects, and those left by settlers.

Previously in tunnel work zones around Sodo and South Lake Union, archaeologists found a cedar rope, but little else in the way of native objects, Archer said.

If the new search turns up something, then “we’re going to have that conversation (about how much more time and digging might be needed), after we know what we’re looking at,” Archer told reporters.

In 2004, WSDOT’s construction of a dry dock in Port Angeles unearthed the remains of 335 people in a buried native village, known as Tse-whit-zen. The state moved its project, at a cost of $60 million to taxpayers.

Archer said the state has offered to share information with the Tulalip, Muckleshoot, Suquamish, Snoqualmie and Duwamish tribes.

In the 19th century, saloons and a gun shop operated near Bertha’s location, while natives traded and camped nearby, so there could be treasures, according to local writer Knute Berger. Ships from San Francisco dumped rock ballast, and fill soil was later deposited from regrades.

In other developments:

• The state canceled its plan to form a team of international experts to help figure out what stopped the world-record, 571
/
3-foot diameter machine Dec. 6, and to give advice for a restart.

WSDOT leaders admit it’s been difficult to recruit people. But Matt Preedy, deputy project administrator, said the primary reason is the project’s two existing oversight panels
provide enough expertise. Another complication is that the state could take on financial risk if it meddles too much with STP, which is responsible for choosing tunneling strategies under the design-build contracting method. Asked about this dilemma, Preedy said, “I don’t really have anything to speculate on that.”

• The repair pit will be circular rather than square, Preedy said Thursday. This is because an arc is stronger than flat walls, to resist pressure from soil or groundwater.

Therefore, STP would need less internal bracing, which frees up space for heavy equipment to move, Preedy said. STP submitted a draft plan that is being reviewed by WSDOT this week. A full repair plan from Hitachi, the machine’s manufacturer, is expected near the end of March.

Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com. On Twitter @mikelindblom