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WSDOT says steel pipe is cause of Bertha blockage

The Washington Department of Transportation says a steel pipe is at least partly to blame for halting the Seattle tunnel project. (WSDOT image)
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After weeks of trying to figure out what's blocking Bertha, the Washington Department of Transportation says a steel pipe is at least partly to blame for halting the Seattle tunnel project. And they knew it was there the whole time.

WSDOT says crews finally were able to lower water pressure and remove enough soil from in front of the world's largest drilling machine to inspect the top 15 feet of the chamber.

"This inspection showed an 8-inch-diameter steel pipe protruding through one of the many openings in the cutterhead. We believe the steel pipe is a well casing installed by WSDOT in 2002 after the 2001 Nisqually earthquake to better understand how groundwater flows through this area," said a statement from WSDOT.

Officials admit the pipe's location was charted in reference materials used to plan the project. But at a press conference announcing the findings, Matt Preedy, WSDOT Alaskan Way Viaduct Replacement Program Deputy Administrator, refused to comment on whether someone failed to read the documentation or alert project engineers about the pipe.

The pipe has damaged the tunnel machine, but it's too soon to determine the extent of the damage.

"What we're faced with right now is a cutter head that needs more cutting tools replaced before we can mine forward," said Chris Dixon, Seattle Tunnel Partners project manager.

It's too soon to determine the cost or timetable for repairs, and the impact on the overall project schedule, Dixon said.

"It's a very challenging environment underground, there's only so much we can do from the surface, there's only so much we can do from the TVM [tunnel machine]," Dixon said.

A source told KIRO Radio Dec. 25 that officials knew then about the pipe and damage to Bertha, but officials continued to deny it until Friday's revelations despite repeated inquiries.

Preedy admitted at the news conference they knew Bertha was damaged several weeks ago. But he insisted they didn't know if it was caused by a foreign object or normal wear until this week's inspection.

WSDOT says other potential factors include changing soil conditions that may have caused excessive wear of cutting tools, potential objects in front of the cutterhead or objects in the lower portion of the excavation chamber that still aren't visible.

"We have probed 12 holes and encountered other obstructions in six of those holes," said Dixon. Those obstructions are believed to be metallic as well. Bertha can't cut through metal despite it's massive size.

"We'll continue to work with STP to determine ways to make up time lost during the blockage. Our focus is now on addressing this issue safely and in a timely manner so we can resume tunneling as soon as possible," Preedy said.

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