Repairing the largest tunnel boring machine ever built poses a immense challenge to the ingenuity and resources of engineering experts in Seattle.

Big Bertha is the largest tunnel boring machine ever built in terms of diameter, measuring 17.5 metres, or almost six storeys in height, from top to bottom. The machine was designed for the specific purpose of burrowing beneath the waterfront of Seattle as part of the US$3.1 billion Alaskan Way Viaduct…