On April 4, the world's largest tunnel boring machine broke through to the open air after almost four years underground. Called Bertha, the giant digger was tasked with the challenge of building a tunnel large enough to carry four lanes of motor traffic under the heart of Seattle. The story of how it made the 1.7 mi (2.7 km) journey under the skyscrapers of the port city [newatlas.com] is not only a tale of a remarkable machine, but also of civil engineering, geology, politics, luck, and proving the old adage that anything that can go wrong, will.
It's an interesting story in its own right, made more timely by announcements that Elon Musk has formed a tunneling company to alleviate traffic.