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in the United States and around the world. His many years of experi- ence deep in tunnels around the world helped to prepare him for his toughest tunneling job yet: the Seattle tunnel. Dixon knew the TBM’s cutter head needed major repairs. Locat- ed on the front of the machine, the cutter head is covered with steel teeth and spinning blades. Buried deep inside the tunnel, however, the cutter head was awfully hard to access. That far underground, the pressure is enormous, and the area in front of the machine was often filled with water. For workers to make repairs, they’d need to wear special breathing equipment, like scuba divers do. It would be time-consuming and dangerous work. Dixon and his team needed to find a better way to repair the machine.

Engineers depend on the many, sharp, metal teeth of tunnel-boring machines like this one to turn their underground designs into reality.

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