World's largest tunneling machine digs in: "Bertha, the world’s largest tunnel boring machine (TBM), started digging under Seattle on Tuesday as it chewed through the north wall of the 80-ft (24.3 m) deep trench where it was assembled after being shipped in pieces from its manufacturer in Japan. Designed to bore a 1.7 mi (2.7 km) tunnel for State Route 99 (SR 99) under the Seattle city center to replace the old viaduct, the machine will both dig out soil and lay a concrete tunnel wall as it goes."
'via Blog this'
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