9781422284827

What do you do when you have big trouble deep in a tunnel? You dig some more! After exploring several possible options, Dixon and the other engineers decided to dig an enormous rescue hole. It would be 120 feet (36 m) deep and lined with concrete. The edge of the hole would be about 20 feet (6.1 m) from where Bertha rested. After excavating the hole, engineers would slowly move the TBM forward until it broke through the concrete wall. Once the cutter head was exposed, workers could detach it and haul it to the surface us- ing a massive lift tower. Pulling the front section of the machine out of the ground would be no easy task. It weighed nearly 2,000 tons! Laid on the ground, the front pieces of the machine would be 30 feet (10 m) tall. Dixon knew that working above the ground would be far easier than working in the muck at the bottom of a pit.Workers would replace the seals and repair the damaged teeth and cutting blades. The crew would then lower the cutter head back into the rescue shaft and reattach it. It took many days of work by dozens of experts, but the massive repair job was done. Dixon cranked up the power, and Bertha got back in action. The run-in with the steel pipe may not be the last setback for the tunnel. Dixon, like any other successful civil engineer, is pre- pared to find solutions to each new problem that arises—whether that problem is on the surface or far beneath our feet.

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