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Project manager Chris Dixon and the other civil engineers working on the tunnel had a big problem on their hands. Bertha was overheating, and they didn’t know why. Dixon was aware that the tunnel borer hit a pipe a few days before. Was it possible that a tiny pipe was capable of halting a 6,700-ton boulder crusher like Bertha? The crew pulled a 55-foot (16.7 m) portion of a pipe out of the ground and away from Bertha’s jaws. They also climbed into the ma- chine and removed pipe fragments.The machine still was not working right. Dixon was puzzled, but he was confident that he and his team could figure it out and get Bertha moving again. They had to diagnose the problem so they could fix it and prevent it from happening again. How do you diagnose a problemwhen all of the clues are underground and covered in dirt and grime? Dixon revved up the machine’s motors in an effort to dislodge whatever was keeping it frommoving forward, but the machine over- heated and mud flowed in. He sent crews into the belly of the machine to clear away the dirt trapped inside. Bertha was still overheating. Finally, workers thought they’d found the cause of the extreme heat. Internal seals that kept out dirt must have been damaged when Ber- tha ate through the steel pipe. After all, the TBM was built to break up rock and loosen debris. It was not built to chew through steel. “These things do happen on tunnel projects,” said Dixon. “We’re really testing the limits for tunnel-boring machines.” He had to figure out how to fix Bertha, knowing that, as he said, the repairs presented “a significant engineering challenge that must be done safely.” Dixon grew up surrounded by construction. His family built things, and so does he. At 16, he got his first job working as a tunnel miner in Australia. He has spent most of his career working on tunnel projects

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