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Underneath Seattle: Working Under Pressure to Keep Bertha Moving

Every tunneling machine needs its cutting tools replaced every now and then. But the challenge is keeping a giant machine sharp while a wall of waterlogged earth looms in front. Welcome to the world of hyperbaric interventions, where crews used compressed air to stabilize the ground and safely complete this high pressure work. This video takes you 200 feet underground for a rare look at hyperbaric work inside Seattle’s SR 99 tunneling machine, Bertha. [Source: WSDOT YouTube Channel. Image: YouTube]