About 20 workers wearing hard hats and reflective vests clump together on the edge of a chasm near Seattle’s waterfront, peering down a hole 120 feet deep and 83 feet wide. The last men have been craned out of the pit in a yellow metal cage. Gulls squawk. A TV news helicopter hovers overhead.

A dozen journalists stand nearby on the bed of a truck. We’re here to see Bertha, one of the world’s biggest tunneling machines. Or at least a piece of her. A 240-foot crane is about to haul a 540,000-pound steel shield out of the ground, 20 months after Bertha started digging a highway. Almost imperceptibly, the crane starts rising

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