RACHEL MARTIN, HOST: This is WEEKEND EDITION from NPR News. I'm Rachel Martin. The people of Seattle are puzzled by a mystery unfolding underground: the world's biggest tunneling machine is stuck about 75 feet under street level where it's digging a nearly two-mile-long highway right under downtown Seattle. As NPR's Martin Kaste reports, engineers say it'll take until January to figure out what is causing the block.</s>MARTIN KASTE, BYLINE: They call the machine Bertha, and it has a circular cutting face five stories high, with special attachments for chewing up boulders. But only 1,000 feet into the job, it seems to have encountered an object that refuses to yield. Seattleites have had fun guessing what that might be - a sunken ship, a Native curse, Jimmy Hoffa. But project manager Chris Dixon won't be drawn into that game.</s>CHRIS DIXON: I wouldn't bet on it being one thing or the other thing.</s>MARTIN KASTE, BYLINE: Though Dixon admits the situation is mysterious.</s>CHRIS DIXON: Theoretically, there shouldn't be any obstructions at that depth. But I guess there were several channels that went down through the native soils before they filled this area. So, we could...</s>MARTIN KASTE, BYLINE: Like river channels.</s>CHRIS DIXON: Yeah. So, we could have encountered something that was dumped into a deep channel through that area. But, again, we don't won't know what it is until we do an investigation.</s>MARTIN KASTE, BYLINE: But on a tunneling machine, you can't just open a window to see what's ahead. Crews at street level are now drilling ten wells to pump the ground water away from Bertha. The idea is to relieve the pressure enough to make things a little more hospitable for the workers when they finally crawl out of specialized hatches to inspect the situation. And there's a chance they'll find no mystery object at all. It may just be that Bertha's just broken. Martin Kaste, NPR News, Seattle.
In Seattle, an underground mystery has halted the digging of a new highway tunnel underneath downtown. The world's largest tunneling machine ground to a halt two weeks ago, and engineers are still trying to figure out why.